From 5d9dfbd08f38c2a9bc71d39de8f5c7776afe0f9e Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <n.nethercote@gmail.com>
Date: Sun, 14 Jan 2024 10:57:07 +1100
Subject: [PATCH] Stop using `String` for error codes.

Error codes are integers, but `String` is used everywhere to represent
them. Gross!

This commit introduces `ErrCode`, an integral newtype for error codes,
replacing `String`. It also introduces a constant for every error code,
e.g. `E0123`, and removes the `error_code!` macro. The constants are
imported wherever used with `use rustc_errors::codes::*`.

With the old code, we have three different ways to specify an error code
at a use point:
```
error_code!(E0123)  // macro call

struct_span_code_err!(dcx, span, E0123, "msg");  // bare ident arg to macro call

\#[diag(name, code = "E0123")]  // string
struct Diag;
```

With the new code, they all use the `E0123` constant.
```
E0123  // constant

struct_span_code_err!(dcx, span, E0123, "msg");  // constant

\#[diag(name, code = E0123)]  // constant
struct Diag;
```

The commit also changes the structure of the error code definitions:
- `rustc_error_codes` now just defines a higher-order macro listing the
  used error codes and nothing else.
- Because that's now the only thing in the `rustc_error_codes` crate, I
  moved it into the `lib.rs` file and removed the `error_codes.rs` file.
- `rustc_errors` uses that macro to define everything, e.g. the error
  code constants and the `DIAGNOSTIC_TABLES`. This is in its new
  `codes.rs` file.
---
 Cargo.lock                                    |   4 +-
 compiler/rustc_ast_lowering/src/errors.rs     |  20 +-
 compiler/rustc_ast_passes/src/errors.rs       |  38 +-
 .../rustc_attr/src/session_diagnostics.rs     |  47 +-
 .../rustc_borrowck/src/borrowck_errors.rs     |   2 +-
 .../src/diagnostics/conflict_errors.rs        |   4 +-
 .../rustc_borrowck/src/session_diagnostics.rs |   8 +-
 compiler/rustc_builtin_macros/src/errors.rs   |   8 +-
 compiler/rustc_codegen_ssa/src/back/write.rs  |   4 +-
 .../rustc_codegen_ssa/src/codegen_attrs.rs    |   2 +-
 compiler/rustc_codegen_ssa/src/errors.rs      |  80 +--
 compiler/rustc_const_eval/src/errors.rs       |  52 +-
 .../src/transform/check_consts/ops.rs         |  14 +-
 compiler/rustc_driver_impl/Cargo.toml         |   1 -
 compiler/rustc_driver_impl/src/lib.rs         |  58 +-
 compiler/rustc_error_codes/src/error_codes.rs | 658 -----------------
 compiler/rustc_error_codes/src/lib.rs         | 678 +++++++++++++++++-
 compiler/rustc_errors/Cargo.toml              |   2 +
 .../src/annotate_snippet_emitter_writer.rs    |   7 +-
 compiler/rustc_errors/src/codes.rs            |  39 +
 compiler/rustc_errors/src/diagnostic.rs       |  17 +-
 .../rustc_errors/src/diagnostic_builder.rs    |  13 +-
 compiler/rustc_errors/src/diagnostic_impls.rs |   3 +-
 compiler/rustc_errors/src/emitter.rs          |  12 +-
 compiler/rustc_errors/src/json.rs             |   4 +-
 compiler/rustc_errors/src/lib.rs              |  19 +-
 compiler/rustc_errors/src/registry.rs         |   9 +-
 compiler/rustc_expand/src/errors.rs           |  11 +-
 .../rustc_hir_analysis/src/astconv/bounds.rs  |   2 +-
 .../rustc_hir_analysis/src/astconv/errors.rs  |   4 +-
 .../src/astconv/generics.rs                   |   4 +-
 .../rustc_hir_analysis/src/astconv/lint.rs    |   2 +-
 .../rustc_hir_analysis/src/astconv/mod.rs     |  10 +-
 .../src/astconv/object_safety.rs              |   2 +-
 .../rustc_hir_analysis/src/check/check.rs     |   2 +-
 .../src/check/compare_impl_item.rs            |   4 +-
 .../rustc_hir_analysis/src/check/dropck.rs    |   2 +-
 .../rustc_hir_analysis/src/check/intrinsic.rs |   2 +-
 .../rustc_hir_analysis/src/check/wfcheck.rs   |   2 +-
 .../src/coherence/inherent_impls_overlap.rs   |   2 +-
 .../rustc_hir_analysis/src/coherence/mod.rs   |   4 +-
 .../src/coherence/unsafety.rs                 |   2 +-
 .../src/collect/resolve_bound_vars.rs         |   2 +-
 compiler/rustc_hir_analysis/src/errors.rs     | 140 ++--
 .../rustc_hir_analysis/src/impl_wf_check.rs   |   2 +-
 .../src/structured_errors.rs                  |   6 +-
 .../missing_cast_for_variadic_arg.rs          |   6 +-
 .../structured_errors/sized_unsized_cast.rs   |   6 +-
 .../wrong_number_of_generic_args.rs           |   8 +-
 compiler/rustc_hir_typeck/src/cast.rs         |   2 +-
 compiler/rustc_hir_typeck/src/coercion.rs     |   4 +-
 compiler/rustc_hir_typeck/src/errors.rs       |  34 +-
 compiler/rustc_hir_typeck/src/expr.rs         |  12 +-
 .../rustc_hir_typeck/src/fn_ctxt/checks.rs    |  12 +-
 compiler/rustc_hir_typeck/src/intrinsicck.rs  |   2 +-
 compiler/rustc_hir_typeck/src/lib.rs          |  10 +-
 .../rustc_hir_typeck/src/method/suggest.rs    |   7 +-
 compiler/rustc_hir_typeck/src/op.rs           |   4 +-
 compiler/rustc_hir_typeck/src/pat.rs          |  14 +-
 compiler/rustc_infer/src/errors/mod.rs        |  66 +-
 .../src/infer/error_reporting/mod.rs          |   8 +-
 .../infer/error_reporting/need_type_info.rs   |  12 +-
 .../infer/error_reporting/note_and_explain.rs |   4 +-
 .../src/traits/error_reporting/mod.rs         |   2 +-
 compiler/rustc_lint/src/errors.rs             |  14 +-
 compiler/rustc_lint/src/lints.rs              |   6 +-
 .../src/diagnostics/diagnostic_builder.rs     |   4 +-
 compiler/rustc_macros/src/diagnostics/mod.rs  |   2 +-
 compiler/rustc_metadata/src/errors.rs         |  28 +-
 compiler/rustc_middle/src/error.rs            |   4 +-
 compiler/rustc_middle/src/values.rs           |   2 +-
 compiler/rustc_mir_build/src/errors.rs        |  64 +-
 .../src/thir/pattern/check_match.rs           |   2 +-
 .../rustc_mir_build/src/thir/pattern/mod.rs   |   4 +-
 compiler/rustc_mir_transform/src/errors.rs    |   6 +-
 compiler/rustc_parse/src/errors.rs            |  18 +-
 compiler/rustc_parse/src/lexer/mod.rs         |  16 +-
 compiler/rustc_parse/src/parser/attr.rs       |   4 +-
 compiler/rustc_parse/src/parser/item.rs       |   2 +-
 compiler/rustc_passes/src/entry.rs            |   6 +-
 compiler/rustc_passes/src/errors.rs           |  94 +--
 compiler/rustc_privacy/src/errors.rs          |   6 +-
 compiler/rustc_query_system/src/error.rs      |   3 +-
 .../rustc_resolve/src/build_reduced_graph.rs  |   2 +-
 compiler/rustc_resolve/src/diagnostics.rs     |   4 +-
 compiler/rustc_resolve/src/errors.rs          |  63 +-
 compiler/rustc_resolve/src/imports.rs         |   2 +-
 compiler/rustc_resolve/src/late.rs            |  54 +-
 .../rustc_resolve/src/late/diagnostics.rs     |  14 +-
 compiler/rustc_resolve/src/lib.rs             |   4 +-
 compiler/rustc_resolve/src/macros.rs          |   2 +-
 compiler/rustc_session/src/errors.rs          |   6 +-
 compiler/rustc_session/src/session.rs         |   6 +-
 compiler/rustc_trait_selection/src/errors.rs  |  20 +-
 .../traits/error_reporting/infer_ctxt_ext.rs  |   2 +-
 .../error_reporting/on_unimplemented.rs       |   2 +-
 .../src/traits/error_reporting/suggestions.rs |   4 +-
 .../error_reporting/type_err_ctxt_ext.rs      |   8 +-
 .../src/traits/specialize/mod.rs              |   4 +-
 compiler/rustc_ty_utils/src/errors.rs         |   3 +-
 src/librustdoc/clean/mod.rs                   |   5 +-
 src/librustdoc/core.rs                        |   2 +-
 src/tools/error_index_generator/Cargo.toml    |   1 -
 src/tools/error_index_generator/main.rs       |   8 +-
 src/tools/tidy/src/error_codes.rs             |  34 +-
 .../session-diagnostic/diagnostic-derive.rs   | 166 ++---
 .../diagnostic-derive.stderr                  | 268 +++----
 .../session-diagnostic/enforce_slug_naming.rs |   2 +-
 .../enforce_slug_naming.stderr                |   2 +-
 triagebot.toml                                |   2 +-
 110 files changed, 1624 insertions(+), 1572 deletions(-)
 delete mode 100644 compiler/rustc_error_codes/src/error_codes.rs
 create mode 100644 compiler/rustc_errors/src/codes.rs

diff --git a/Cargo.lock b/Cargo.lock
index 454ec90b9af..d645957da96 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1268,7 +1268,6 @@ name = "error_index_generator"
 version = "0.0.0"
 dependencies = [
  "mdbook",
- "rustc_error_codes",
 ]
 
 [[package]]
@@ -3701,7 +3700,6 @@ dependencies = [
  "rustc_codegen_ssa",
  "rustc_const_eval",
  "rustc_data_structures",
- "rustc_error_codes",
  "rustc_errors",
  "rustc_expand",
  "rustc_feature",
@@ -3774,9 +3772,11 @@ dependencies = [
  "rustc_ast",
  "rustc_ast_pretty",
  "rustc_data_structures",
+ "rustc_error_codes",
  "rustc_error_messages",
  "rustc_fluent_macro",
  "rustc_hir",
+ "rustc_index",
  "rustc_lint_defs",
  "rustc_macros",
  "rustc_serialize",
diff --git a/compiler/rustc_ast_lowering/src/errors.rs b/compiler/rustc_ast_lowering/src/errors.rs
index 4843d36372d..51bb8a96fad 100644
--- a/compiler/rustc_ast_lowering/src/errors.rs
+++ b/compiler/rustc_ast_lowering/src/errors.rs
@@ -1,9 +1,9 @@
-use rustc_errors::DiagnosticArgFromDisplay;
+use rustc_errors::{codes::*, DiagnosticArgFromDisplay};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::{symbol::Ident, Span, Symbol};
 
 #[derive(Diagnostic, Clone, Copy)]
-#[diag(ast_lowering_generic_type_with_parentheses, code = "E0214")]
+#[diag(ast_lowering_generic_type_with_parentheses, code = E0214)]
 pub struct GenericTypeWithParentheses {
     #[primary_span]
     #[label]
@@ -22,7 +22,7 @@ pub struct UseAngleBrackets {
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_lowering_invalid_abi, code = "E0703")]
+#[diag(ast_lowering_invalid_abi, code = E0703)]
 #[note]
 pub struct InvalidAbi {
     #[primary_span]
@@ -89,7 +89,7 @@ pub enum AssocTyParenthesesSub {
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_lowering_misplaced_impl_trait, code = "E0562")]
+#[diag(ast_lowering_misplaced_impl_trait, code = E0562)]
 #[note]
 pub struct MisplacedImplTrait<'a> {
     #[primary_span]
@@ -114,7 +114,7 @@ pub struct UnderscoreExprLhsAssign {
 }
 
 #[derive(Diagnostic, Clone, Copy)]
-#[diag(ast_lowering_base_expression_double_dot, code = "E0797")]
+#[diag(ast_lowering_base_expression_double_dot, code = E0797)]
 pub struct BaseExpressionDoubleDot {
     #[primary_span]
     #[suggestion(code = "/* expr */", applicability = "has-placeholders", style = "verbose")]
@@ -122,7 +122,7 @@ pub struct BaseExpressionDoubleDot {
 }
 
 #[derive(Diagnostic, Clone, Copy)]
-#[diag(ast_lowering_await_only_in_async_fn_and_blocks, code = "E0728")]
+#[diag(ast_lowering_await_only_in_async_fn_and_blocks, code = E0728)]
 pub struct AwaitOnlyInAsyncFnAndBlocks {
     #[primary_span]
     #[label]
@@ -132,14 +132,14 @@ pub struct AwaitOnlyInAsyncFnAndBlocks {
 }
 
 #[derive(Diagnostic, Clone, Copy)]
-#[diag(ast_lowering_coroutine_too_many_parameters, code = "E0628")]
+#[diag(ast_lowering_coroutine_too_many_parameters, code = E0628)]
 pub struct CoroutineTooManyParameters {
     #[primary_span]
     pub fn_decl_span: Span,
 }
 
 #[derive(Diagnostic, Clone, Copy)]
-#[diag(ast_lowering_closure_cannot_be_static, code = "E0697")]
+#[diag(ast_lowering_closure_cannot_be_static, code = E0697)]
 pub struct ClosureCannotBeStatic {
     #[primary_span]
     pub fn_decl_span: Span,
@@ -154,14 +154,14 @@ pub struct FunctionalRecordUpdateDestructuringAssignment {
 }
 
 #[derive(Diagnostic, Clone, Copy)]
-#[diag(ast_lowering_async_coroutines_not_supported, code = "E0727")]
+#[diag(ast_lowering_async_coroutines_not_supported, code = E0727)]
 pub struct AsyncCoroutinesNotSupported {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic, Clone, Copy)]
-#[diag(ast_lowering_inline_asm_unsupported_target, code = "E0472")]
+#[diag(ast_lowering_inline_asm_unsupported_target, code = E0472)]
 pub struct InlineAsmUnsupportedTarget {
     #[primary_span]
     pub span: Span,
diff --git a/compiler/rustc_ast_passes/src/errors.rs b/compiler/rustc_ast_passes/src/errors.rs
index e2b8e64b115..5f54a0ddf8c 100644
--- a/compiler/rustc_ast_passes/src/errors.rs
+++ b/compiler/rustc_ast_passes/src/errors.rs
@@ -1,7 +1,7 @@
 //! Errors emitted by ast_passes.
 
 use rustc_ast::ParamKindOrd;
-use rustc_errors::{AddToDiagnostic, Applicability};
+use rustc_errors::{codes::*, AddToDiagnostic, Applicability};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::{symbol::Ident, Span, Symbol};
 
@@ -23,7 +23,7 @@ pub struct InvalidLabel {
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_visibility_not_permitted, code = "E0449")]
+#[diag(ast_passes_visibility_not_permitted, code = E0449)]
 pub struct VisibilityNotPermitted {
     #[primary_span]
     pub span: Span,
@@ -44,7 +44,7 @@ pub enum VisibilityNotPermittedNote {
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_trait_fn_const, code = "E0379")]
+#[diag(ast_passes_trait_fn_const, code = E0379)]
 pub struct TraitFnConst {
     #[primary_span]
     #[label]
@@ -302,14 +302,14 @@ pub struct ItemUnderscore<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_nomangle_ascii, code = "E0754")]
+#[diag(ast_passes_nomangle_ascii, code = E0754)]
 pub struct NoMangleAscii {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_module_nonascii, code = "E0754")]
+#[diag(ast_passes_module_nonascii, code = E0754)]
 #[help]
 pub struct ModuleNonAscii {
     #[primary_span]
@@ -318,7 +318,7 @@ pub struct ModuleNonAscii {
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_auto_generic, code = "E0567")]
+#[diag(ast_passes_auto_generic, code = E0567)]
 pub struct AutoTraitGeneric {
     #[primary_span]
     #[suggestion(code = "", applicability = "machine-applicable")]
@@ -328,7 +328,7 @@ pub struct AutoTraitGeneric {
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_auto_super_lifetime, code = "E0568")]
+#[diag(ast_passes_auto_super_lifetime, code = E0568)]
 pub struct AutoTraitBounds {
     #[primary_span]
     #[suggestion(code = "", applicability = "machine-applicable")]
@@ -338,7 +338,7 @@ pub struct AutoTraitBounds {
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_auto_items, code = "E0380")]
+#[diag(ast_passes_auto_items, code = E0380)]
 pub struct AutoTraitItems {
     #[primary_span]
     pub spans: Vec<Span>,
@@ -384,28 +384,28 @@ fn add_to_diagnostic_with<F>(self, diag: &mut rustc_errors::Diagnostic, _: F)
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_pattern_in_fn_pointer, code = "E0561")]
+#[diag(ast_passes_pattern_in_fn_pointer, code = E0561)]
 pub struct PatternFnPointer {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_trait_object_single_bound, code = "E0226")]
+#[diag(ast_passes_trait_object_single_bound, code = E0226)]
 pub struct TraitObjectBound {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_impl_trait_path, code = "E0667")]
+#[diag(ast_passes_impl_trait_path, code = E0667)]
 pub struct ImplTraitPath {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_nested_impl_trait, code = "E0666")]
+#[diag(ast_passes_nested_impl_trait, code = E0666)]
 pub struct NestedImplTrait {
     #[primary_span]
     pub span: Span,
@@ -443,7 +443,7 @@ pub struct ObsoleteAuto {
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_unsafe_negative_impl, code = "E0198")]
+#[diag(ast_passes_unsafe_negative_impl, code = E0198)]
 pub struct UnsafeNegativeImpl {
     #[primary_span]
     pub span: Span,
@@ -468,7 +468,7 @@ pub struct InherentImplCannot<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_inherent_cannot_be, code = "E0197")]
+#[diag(ast_passes_inherent_cannot_be, code = E0197)]
 pub struct InherentImplCannotUnsafe<'a> {
     #[primary_span]
     pub span: Span,
@@ -536,7 +536,7 @@ pub struct GenericDefaultTrailing {
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_nested_lifetimes, code = "E0316")]
+#[diag(ast_passes_nested_lifetimes, code = E0316)]
 pub struct NestedLifetimes {
     #[primary_span]
     pub span: Span,
@@ -655,7 +655,7 @@ pub struct ConstAndCVariadic {
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_pattern_in_foreign, code = "E0130")]
+#[diag(ast_passes_pattern_in_foreign, code = E0130)]
 pub struct PatternInForeign {
     #[primary_span]
     #[label]
@@ -663,7 +663,7 @@ pub struct PatternInForeign {
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_pattern_in_bodiless, code = "E0642")]
+#[diag(ast_passes_pattern_in_bodiless, code = E0642)]
 pub struct PatternInBodiless {
     #[primary_span]
     #[label]
@@ -711,14 +711,14 @@ pub struct AssociatedSuggestion2 {
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_stability_outside_std, code = "E0734")]
+#[diag(ast_passes_stability_outside_std, code = E0734)]
 pub struct StabilityOutsideStd {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_feature_on_non_nightly, code = "E0554")]
+#[diag(ast_passes_feature_on_non_nightly, code = E0554)]
 pub struct FeatureOnNonNightly {
     #[primary_span]
     pub span: Span,
diff --git a/compiler/rustc_attr/src/session_diagnostics.rs b/compiler/rustc_attr/src/session_diagnostics.rs
index 315a00c8d2f..79370602842 100644
--- a/compiler/rustc_attr/src/session_diagnostics.rs
+++ b/compiler/rustc_attr/src/session_diagnostics.rs
@@ -2,8 +2,7 @@
 
 use rustc_ast as ast;
 use rustc_errors::{
-    error_code, Applicability, DiagCtxt, DiagnosticBuilder, EmissionGuarantee, IntoDiagnostic,
-    Level,
+    codes::*, Applicability, DiagCtxt, DiagnosticBuilder, EmissionGuarantee, IntoDiagnostic, Level,
 };
 use rustc_macros::Diagnostic;
 use rustc_span::{Span, Symbol};
@@ -12,14 +11,14 @@
 use crate::UnsupportedLiteralReason;
 
 #[derive(Diagnostic)]
-#[diag(attr_expected_one_cfg_pattern, code = "E0536")]
+#[diag(attr_expected_one_cfg_pattern, code = E0536)]
 pub(crate) struct ExpectedOneCfgPattern {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_invalid_predicate, code = "E0537")]
+#[diag(attr_invalid_predicate, code = E0537)]
 pub(crate) struct InvalidPredicate {
     #[primary_span]
     pub span: Span,
@@ -28,7 +27,7 @@ pub(crate) struct InvalidPredicate {
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_multiple_item, code = "E0538")]
+#[diag(attr_multiple_item, code = E0538)]
 pub(crate) struct MultipleItem {
     #[primary_span]
     pub span: Span,
@@ -37,7 +36,7 @@ pub(crate) struct MultipleItem {
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_incorrect_meta_item, code = "E0539")]
+#[diag(attr_incorrect_meta_item, code = E0539)]
 pub(crate) struct IncorrectMetaItem {
     #[primary_span]
     pub span: Span,
@@ -56,7 +55,7 @@ fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> DiagnosticBuilder<'
         let expected = self.expected.iter().map(|name| format!("`{name}`")).collect::<Vec<_>>();
         DiagnosticBuilder::new(dcx, level, fluent::attr_unknown_meta_item)
             .with_span(self.span)
-            .with_code(error_code!(E0541))
+            .with_code(E0541)
             .with_arg("item", self.item)
             .with_arg("expected", expected.join(", "))
             .with_span_label(self.span, fluent::attr_label)
@@ -64,28 +63,28 @@ fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> DiagnosticBuilder<'
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_missing_since, code = "E0542")]
+#[diag(attr_missing_since, code = E0542)]
 pub(crate) struct MissingSince {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_missing_note, code = "E0543")]
+#[diag(attr_missing_note, code = E0543)]
 pub(crate) struct MissingNote {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_multiple_stability_levels, code = "E0544")]
+#[diag(attr_multiple_stability_levels, code = E0544)]
 pub(crate) struct MultipleStabilityLevels {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_invalid_issue_string, code = "E0545")]
+#[diag(attr_invalid_issue_string, code = E0545)]
 pub(crate) struct InvalidIssueString {
     #[primary_span]
     pub span: Span,
@@ -143,21 +142,21 @@ pub fn from_int_error_kind(span: Span, kind: &IntErrorKind) -> Option<Self> {
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_missing_feature, code = "E0546")]
+#[diag(attr_missing_feature, code = E0546)]
 pub(crate) struct MissingFeature {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_non_ident_feature, code = "E0546")]
+#[diag(attr_non_ident_feature, code = E0546)]
 pub(crate) struct NonIdentFeature {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_missing_issue, code = "E0547")]
+#[diag(attr_missing_issue, code = E0547)]
 pub(crate) struct MissingIssue {
     #[primary_span]
     pub span: Span,
@@ -166,14 +165,14 @@ pub(crate) struct MissingIssue {
 // FIXME: Why is this the same error code as `InvalidReprHintNoParen` and `InvalidReprHintNoValue`?
 // It is more similar to `IncorrectReprFormatGeneric`.
 #[derive(Diagnostic)]
-#[diag(attr_incorrect_repr_format_packed_one_or_zero_arg, code = "E0552")]
+#[diag(attr_incorrect_repr_format_packed_one_or_zero_arg, code = E0552)]
 pub(crate) struct IncorrectReprFormatPackedOneOrZeroArg {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_invalid_repr_hint_no_paren, code = "E0552")]
+#[diag(attr_invalid_repr_hint_no_paren, code = E0552)]
 pub(crate) struct InvalidReprHintNoParen {
     #[primary_span]
     pub span: Span,
@@ -182,7 +181,7 @@ pub(crate) struct InvalidReprHintNoParen {
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_invalid_repr_hint_no_value, code = "E0552")]
+#[diag(attr_invalid_repr_hint_no_value, code = E0552)]
 pub(crate) struct InvalidReprHintNoValue {
     #[primary_span]
     pub span: Span,
@@ -215,7 +214,7 @@ fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> DiagnosticBuilder<'
             },
         );
         diag.span(self.span);
-        diag.code(error_code!(E0565));
+        diag.code(E0565);
         if self.is_bytestr {
             diag.span_suggestion(
                 self.start_point_span,
@@ -229,7 +228,7 @@ fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> DiagnosticBuilder<'
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_invalid_repr_align_need_arg, code = "E0589")]
+#[diag(attr_invalid_repr_align_need_arg, code = E0589)]
 pub(crate) struct InvalidReprAlignNeedArg {
     #[primary_span]
     #[suggestion(code = "align(...)", applicability = "has-placeholders")]
@@ -237,7 +236,7 @@ pub(crate) struct InvalidReprAlignNeedArg {
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_invalid_repr_generic, code = "E0589")]
+#[diag(attr_invalid_repr_generic, code = E0589)]
 pub(crate) struct InvalidReprGeneric<'a> {
     #[primary_span]
     pub span: Span,
@@ -247,14 +246,14 @@ pub(crate) struct InvalidReprGeneric<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_incorrect_repr_format_align_one_arg, code = "E0693")]
+#[diag(attr_incorrect_repr_format_align_one_arg, code = E0693)]
 pub(crate) struct IncorrectReprFormatAlignOneArg {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_incorrect_repr_format_generic, code = "E0693")]
+#[diag(attr_incorrect_repr_format_generic, code = E0693)]
 pub(crate) struct IncorrectReprFormatGeneric<'a> {
     #[primary_span]
     pub span: Span,
@@ -305,14 +304,14 @@ pub fn from_lit_kind(span: Span, kind: &ast::LitKind, name: &'a str) -> Option<S
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_rustc_promotable_pairing, code = "E0717")]
+#[diag(attr_rustc_promotable_pairing, code = E0717)]
 pub(crate) struct RustcPromotablePairing {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(attr_rustc_allowed_unstable_pairing, code = "E0789")]
+#[diag(attr_rustc_allowed_unstable_pairing, code = E0789)]
 pub(crate) struct RustcAllowedUnstablePairing {
     #[primary_span]
     pub span: Span,
diff --git a/compiler/rustc_borrowck/src/borrowck_errors.rs b/compiler/rustc_borrowck/src/borrowck_errors.rs
index 351976cdaea..8a275a83630 100644
--- a/compiler/rustc_borrowck/src/borrowck_errors.rs
+++ b/compiler/rustc_borrowck/src/borrowck_errors.rs
@@ -1,4 +1,4 @@
-use rustc_errors::{struct_span_code_err, DiagCtxt, DiagnosticBuilder};
+use rustc_errors::{codes::*, struct_span_code_err, DiagCtxt, DiagnosticBuilder};
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::Span;
 
diff --git a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
index da67862a48d..2e83072b8d1 100644
--- a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
@@ -3,7 +3,9 @@
 use either::Either;
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::FxIndexSet;
-use rustc_errors::{struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder, MultiSpan};
+use rustc_errors::{
+    codes::*, struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder, MultiSpan,
+};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::intravisit::{walk_block, walk_expr, Visitor};
diff --git a/compiler/rustc_borrowck/src/session_diagnostics.rs b/compiler/rustc_borrowck/src/session_diagnostics.rs
index e321b92603d..1685624f247 100644
--- a/compiler/rustc_borrowck/src/session_diagnostics.rs
+++ b/compiler/rustc_borrowck/src/session_diagnostics.rs
@@ -1,4 +1,4 @@
-use rustc_errors::MultiSpan;
+use rustc_errors::{codes::*, MultiSpan};
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
 use rustc_middle::ty::{GenericArg, Ty};
 use rustc_span::Span;
@@ -6,7 +6,7 @@
 use crate::diagnostics::RegionName;
 
 #[derive(Diagnostic)]
-#[diag(borrowck_move_unsized, code = "E0161")]
+#[diag(borrowck_move_unsized, code = E0161)]
 pub(crate) struct MoveUnsized<'tcx> {
     pub ty: Ty<'tcx>,
     #[primary_span]
@@ -281,7 +281,7 @@ pub(crate) enum CaptureVarCause {
 }
 
 #[derive(Diagnostic)]
-#[diag(borrowck_cannot_move_when_borrowed, code = "E0505")]
+#[diag(borrowck_cannot_move_when_borrowed, code = E0505)]
 pub(crate) struct MoveBorrow<'a> {
     pub place: &'a str,
     pub borrow_place: &'a str,
@@ -294,7 +294,7 @@ pub(crate) struct MoveBorrow<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(borrowck_opaque_type_non_generic_param, code = "E0792")]
+#[diag(borrowck_opaque_type_non_generic_param, code = E0792)]
 pub(crate) struct NonGenericOpaqueTypeParam<'a, 'tcx> {
     pub ty: GenericArg<'tcx>,
     pub kind: &'a str,
diff --git a/compiler/rustc_builtin_macros/src/errors.rs b/compiler/rustc_builtin_macros/src/errors.rs
index d6dfd0efaf9..eadb48ddd36 100644
--- a/compiler/rustc_builtin_macros/src/errors.rs
+++ b/compiler/rustc_builtin_macros/src/errors.rs
@@ -1,6 +1,6 @@
 use rustc_errors::{
-    AddToDiagnostic, DiagCtxt, DiagnosticBuilder, EmissionGuarantee, IntoDiagnostic, Level,
-    MultiSpan, SingleLabelManySpans,
+    codes::*, AddToDiagnostic, DiagCtxt, DiagnosticBuilder, EmissionGuarantee, IntoDiagnostic,
+    Level, MultiSpan, SingleLabelManySpans,
 };
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::{symbol::Ident, Span, Symbol};
@@ -269,7 +269,7 @@ pub(crate) struct ConcatIdentsIdentArgs {
 }
 
 #[derive(Diagnostic)]
-#[diag(builtin_macros_bad_derive_target, code = "E0774")]
+#[diag(builtin_macros_bad_derive_target, code = E0774)]
 pub(crate) struct BadDeriveTarget {
     #[primary_span]
     #[label]
@@ -283,7 +283,7 @@ pub(crate) struct BadDeriveTarget {
 pub(crate) struct TestsNotSupport {}
 
 #[derive(Diagnostic)]
-#[diag(builtin_macros_unexpected_lit, code = "E0777")]
+#[diag(builtin_macros_unexpected_lit, code = E0777)]
 pub(crate) struct BadDeriveLit {
     #[primary_span]
     #[label]
diff --git a/compiler/rustc_codegen_ssa/src/back/write.rs b/compiler/rustc_codegen_ssa/src/back/write.rs
index 5d497d4a188..b13d566b40b 100644
--- a/compiler/rustc_codegen_ssa/src/back/write.rs
+++ b/compiler/rustc_codegen_ssa/src/back/write.rs
@@ -15,7 +15,7 @@
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::emitter::Emitter;
 use rustc_errors::{translation::Translate, DiagCtxt, FatalError, Level};
-use rustc_errors::{DiagnosticBuilder, DiagnosticMessage, Style};
+use rustc_errors::{DiagnosticBuilder, DiagnosticMessage, ErrCode, Style};
 use rustc_fs_util::link_or_copy;
 use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
 use rustc_incremental::{
@@ -1000,7 +1000,7 @@ pub(crate) enum Message<B: WriteBackendMethods> {
 struct Diagnostic {
     msgs: Vec<(DiagnosticMessage, Style)>,
     args: FxHashMap<DiagnosticArgName<'static>, rustc_errors::DiagnosticArgValue<'static>>,
-    code: Option<String>,
+    code: Option<ErrCode>,
     lvl: Level,
 }
 
diff --git a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
index cca239a43b3..47b1b080119 100644
--- a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
+++ b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
@@ -1,6 +1,6 @@
 use rustc_ast::{ast, attr, MetaItemKind, NestedMetaItem};
 use rustc_attr::{list_contains_name, InlineAttr, InstructionSetAttr, OptimizeAttr};
-use rustc_errors::struct_span_code_err;
+use rustc_errors::{codes::*, struct_span_code_err};
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LocalDefId, LOCAL_CRATE};
diff --git a/compiler/rustc_codegen_ssa/src/errors.rs b/compiler/rustc_codegen_ssa/src/errors.rs
index f90e1906caf..ef291ead190 100644
--- a/compiler/rustc_codegen_ssa/src/errors.rs
+++ b/compiler/rustc_codegen_ssa/src/errors.rs
@@ -4,7 +4,7 @@
 use crate::back::command::Command;
 use crate::fluent_generated as fluent;
 use rustc_errors::{
-    DiagCtxt, DiagnosticArgValue, DiagnosticBuilder, EmissionGuarantee, IntoDiagnostic,
+    codes::*, DiagCtxt, DiagnosticArgValue, DiagnosticBuilder, EmissionGuarantee, IntoDiagnostic,
     IntoDiagnosticArg, Level,
 };
 use rustc_macros::Diagnostic;
@@ -612,7 +612,7 @@ pub struct ShuffleIndicesEvaluation {
 
 #[derive(Diagnostic)]
 pub enum InvalidMonomorphization<'tcx> {
-    #[diag(codegen_ssa_invalid_monomorphization_basic_integer_type, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_basic_integer_type, code = E0511)]
     BasicIntegerType {
         #[primary_span]
         span: Span,
@@ -620,7 +620,7 @@ pub enum InvalidMonomorphization<'tcx> {
         ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_basic_float_type, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_basic_float_type, code = E0511)]
     BasicFloatType {
         #[primary_span]
         span: Span,
@@ -628,14 +628,14 @@ pub enum InvalidMonomorphization<'tcx> {
         ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_float_to_int_unchecked, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_float_to_int_unchecked, code = E0511)]
     FloatToIntUnchecked {
         #[primary_span]
         span: Span,
         ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_floating_point_vector, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_floating_point_vector, code = E0511)]
     FloatingPointVector {
         #[primary_span]
         span: Span,
@@ -644,7 +644,7 @@ pub enum InvalidMonomorphization<'tcx> {
         in_ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_floating_point_type, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_floating_point_type, code = E0511)]
     FloatingPointType {
         #[primary_span]
         span: Span,
@@ -652,14 +652,14 @@ pub enum InvalidMonomorphization<'tcx> {
         in_ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_unrecognized_intrinsic, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_unrecognized_intrinsic, code = E0511)]
     UnrecognizedIntrinsic {
         #[primary_span]
         span: Span,
         name: Symbol,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_simd_argument, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_simd_argument, code = E0511)]
     SimdArgument {
         #[primary_span]
         span: Span,
@@ -667,7 +667,7 @@ pub enum InvalidMonomorphization<'tcx> {
         ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_simd_input, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_simd_input, code = E0511)]
     SimdInput {
         #[primary_span]
         span: Span,
@@ -675,7 +675,7 @@ pub enum InvalidMonomorphization<'tcx> {
         ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_simd_first, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_simd_first, code = E0511)]
     SimdFirst {
         #[primary_span]
         span: Span,
@@ -683,7 +683,7 @@ pub enum InvalidMonomorphization<'tcx> {
         ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_simd_second, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_simd_second, code = E0511)]
     SimdSecond {
         #[primary_span]
         span: Span,
@@ -691,7 +691,7 @@ pub enum InvalidMonomorphization<'tcx> {
         ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_simd_third, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_simd_third, code = E0511)]
     SimdThird {
         #[primary_span]
         span: Span,
@@ -699,7 +699,7 @@ pub enum InvalidMonomorphization<'tcx> {
         ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_simd_return, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_simd_return, code = E0511)]
     SimdReturn {
         #[primary_span]
         span: Span,
@@ -707,7 +707,7 @@ pub enum InvalidMonomorphization<'tcx> {
         ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_invalid_bitmask, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_invalid_bitmask, code = E0511)]
     InvalidBitmask {
         #[primary_span]
         span: Span,
@@ -717,7 +717,7 @@ pub enum InvalidMonomorphization<'tcx> {
         expected_bytes: u64,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_return_length_input_type, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_return_length_input_type, code = E0511)]
     ReturnLengthInputType {
         #[primary_span]
         span: Span,
@@ -728,7 +728,7 @@ pub enum InvalidMonomorphization<'tcx> {
         out_len: u64,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_second_argument_length, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_second_argument_length, code = E0511)]
     SecondArgumentLength {
         #[primary_span]
         span: Span,
@@ -739,7 +739,7 @@ pub enum InvalidMonomorphization<'tcx> {
         out_len: u64,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_third_argument_length, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_third_argument_length, code = E0511)]
     ThirdArgumentLength {
         #[primary_span]
         span: Span,
@@ -750,7 +750,7 @@ pub enum InvalidMonomorphization<'tcx> {
         out_len: u64,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_return_integer_type, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_return_integer_type, code = E0511)]
     ReturnIntegerType {
         #[primary_span]
         span: Span,
@@ -759,7 +759,7 @@ pub enum InvalidMonomorphization<'tcx> {
         out_ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_simd_shuffle, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_simd_shuffle, code = E0511)]
     SimdShuffle {
         #[primary_span]
         span: Span,
@@ -767,7 +767,7 @@ pub enum InvalidMonomorphization<'tcx> {
         ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_return_length, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_return_length, code = E0511)]
     ReturnLength {
         #[primary_span]
         span: Span,
@@ -777,7 +777,7 @@ pub enum InvalidMonomorphization<'tcx> {
         out_len: u64,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_return_element, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_return_element, code = E0511)]
     ReturnElement {
         #[primary_span]
         span: Span,
@@ -788,7 +788,7 @@ pub enum InvalidMonomorphization<'tcx> {
         out_ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_shuffle_index_not_constant, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_shuffle_index_not_constant, code = E0511)]
     ShuffleIndexNotConstant {
         #[primary_span]
         span: Span,
@@ -796,7 +796,7 @@ pub enum InvalidMonomorphization<'tcx> {
         arg_idx: u64,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_shuffle_index_out_of_bounds, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_shuffle_index_out_of_bounds, code = E0511)]
     ShuffleIndexOutOfBounds {
         #[primary_span]
         span: Span,
@@ -805,7 +805,7 @@ pub enum InvalidMonomorphization<'tcx> {
         total_len: u128,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_inserted_type, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_inserted_type, code = E0511)]
     InsertedType {
         #[primary_span]
         span: Span,
@@ -815,7 +815,7 @@ pub enum InvalidMonomorphization<'tcx> {
         out_ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_return_type, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_return_type, code = E0511)]
     ReturnType {
         #[primary_span]
         span: Span,
@@ -825,7 +825,7 @@ pub enum InvalidMonomorphization<'tcx> {
         ret_ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_expected_return_type, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_expected_return_type, code = E0511)]
     ExpectedReturnType {
         #[primary_span]
         span: Span,
@@ -834,7 +834,7 @@ pub enum InvalidMonomorphization<'tcx> {
         ret_ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_mismatched_lengths, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_mismatched_lengths, code = E0511)]
     MismatchedLengths {
         #[primary_span]
         span: Span,
@@ -843,7 +843,7 @@ pub enum InvalidMonomorphization<'tcx> {
         v_len: u64,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_mask_type, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_mask_type, code = E0511)]
     MaskType {
         #[primary_span]
         span: Span,
@@ -851,7 +851,7 @@ pub enum InvalidMonomorphization<'tcx> {
         ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_vector_argument, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_vector_argument, code = E0511)]
     VectorArgument {
         #[primary_span]
         span: Span,
@@ -860,7 +860,7 @@ pub enum InvalidMonomorphization<'tcx> {
         in_elem: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_cannot_return, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_cannot_return, code = E0511)]
     CannotReturn {
         #[primary_span]
         span: Span,
@@ -870,7 +870,7 @@ pub enum InvalidMonomorphization<'tcx> {
         expected_bytes: u64,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_expected_element_type, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_expected_element_type, code = E0511)]
     ExpectedElementType {
         #[primary_span]
         span: Span,
@@ -882,7 +882,7 @@ pub enum InvalidMonomorphization<'tcx> {
         mutability: ExpectedPointerMutability,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_third_arg_element_type, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_third_arg_element_type, code = E0511)]
     ThirdArgElementType {
         #[primary_span]
         span: Span,
@@ -891,7 +891,7 @@ pub enum InvalidMonomorphization<'tcx> {
         third_arg: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_unsupported_symbol_of_size, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_unsupported_symbol_of_size, code = E0511)]
     UnsupportedSymbolOfSize {
         #[primary_span]
         span: Span,
@@ -903,7 +903,7 @@ pub enum InvalidMonomorphization<'tcx> {
         ret_ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_unsupported_symbol, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_unsupported_symbol, code = E0511)]
     UnsupportedSymbol {
         #[primary_span]
         span: Span,
@@ -914,7 +914,7 @@ pub enum InvalidMonomorphization<'tcx> {
         ret_ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_cast_fat_pointer, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_cast_fat_pointer, code = E0511)]
     CastFatPointer {
         #[primary_span]
         span: Span,
@@ -922,7 +922,7 @@ pub enum InvalidMonomorphization<'tcx> {
         ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_expected_pointer, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_expected_pointer, code = E0511)]
     ExpectedPointer {
         #[primary_span]
         span: Span,
@@ -930,7 +930,7 @@ pub enum InvalidMonomorphization<'tcx> {
         ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_expected_usize, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_expected_usize, code = E0511)]
     ExpectedUsize {
         #[primary_span]
         span: Span,
@@ -938,7 +938,7 @@ pub enum InvalidMonomorphization<'tcx> {
         ty: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_unsupported_cast, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_unsupported_cast, code = E0511)]
     UnsupportedCast {
         #[primary_span]
         span: Span,
@@ -949,7 +949,7 @@ pub enum InvalidMonomorphization<'tcx> {
         out_elem: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_unsupported_operation, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_unsupported_operation, code = E0511)]
     UnsupportedOperation {
         #[primary_span]
         span: Span,
@@ -958,7 +958,7 @@ pub enum InvalidMonomorphization<'tcx> {
         in_elem: Ty<'tcx>,
     },
 
-    #[diag(codegen_ssa_invalid_monomorphization_expected_vector_element_type, code = "E0511")]
+    #[diag(codegen_ssa_invalid_monomorphization_expected_vector_element_type, code = E0511)]
     ExpectedVectorElementType {
         #[primary_span]
         span: Span,
diff --git a/compiler/rustc_const_eval/src/errors.rs b/compiler/rustc_const_eval/src/errors.rs
index 064d97a49d7..9e27c19e94c 100644
--- a/compiler/rustc_const_eval/src/errors.rs
+++ b/compiler/rustc_const_eval/src/errors.rs
@@ -1,8 +1,8 @@
 use std::borrow::Cow;
 
 use rustc_errors::{
-    DiagCtxt, DiagnosticArgValue, DiagnosticBuilder, DiagnosticMessage, EmissionGuarantee,
-    IntoDiagnostic, Level,
+    codes::*, DiagCtxt, DiagnosticArgValue, DiagnosticBuilder, DiagnosticMessage,
+    EmissionGuarantee, IntoDiagnostic, Level,
 };
 use rustc_hir::ConstContext;
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
@@ -55,14 +55,14 @@ pub(crate) struct UnstableInStable {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_thread_local_access, code = "E0625")]
+#[diag(const_eval_thread_local_access, code = E0625)]
 pub(crate) struct NonConstOpErr {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_static_access, code = "E0013")]
+#[diag(const_eval_static_access, code = E0013)]
 #[help]
 pub(crate) struct StaticAccessErr {
     #[primary_span]
@@ -98,7 +98,7 @@ pub(crate) struct PanicNonStrErr {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_mut_deref, code = "E0658")]
+#[diag(const_eval_mut_deref, code = E0658)]
 pub(crate) struct MutDerefErr {
     #[primary_span]
     pub span: Span,
@@ -106,7 +106,7 @@ pub(crate) struct MutDerefErr {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_transient_mut_borrow, code = "E0658")]
+#[diag(const_eval_transient_mut_borrow, code = E0658)]
 pub(crate) struct TransientMutBorrowErr {
     #[primary_span]
     pub span: Span,
@@ -114,7 +114,7 @@ pub(crate) struct TransientMutBorrowErr {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_transient_mut_raw, code = "E0658")]
+#[diag(const_eval_transient_mut_raw, code = E0658)]
 pub(crate) struct TransientMutRawErr {
     #[primary_span]
     pub span: Span,
@@ -146,7 +146,7 @@ pub(crate) struct UnstableConstFn {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_unallowed_mutable_refs, code = "E0764")]
+#[diag(const_eval_unallowed_mutable_refs, code = E0764)]
 pub(crate) struct UnallowedMutableRefs {
     #[primary_span]
     pub span: Span,
@@ -156,7 +156,7 @@ pub(crate) struct UnallowedMutableRefs {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_unallowed_mutable_raw, code = "E0764")]
+#[diag(const_eval_unallowed_mutable_raw, code = E0764)]
 pub(crate) struct UnallowedMutableRaw {
     #[primary_span]
     pub span: Span,
@@ -165,7 +165,7 @@ pub(crate) struct UnallowedMutableRaw {
     pub teach: Option<()>,
 }
 #[derive(Diagnostic)]
-#[diag(const_eval_non_const_fmt_macro_call, code = "E0015")]
+#[diag(const_eval_non_const_fmt_macro_call, code = E0015)]
 pub(crate) struct NonConstFmtMacroCall {
     #[primary_span]
     pub span: Span,
@@ -173,7 +173,7 @@ pub(crate) struct NonConstFmtMacroCall {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_non_const_fn_call, code = "E0015")]
+#[diag(const_eval_non_const_fn_call, code = E0015)]
 pub(crate) struct NonConstFnCall {
     #[primary_span]
     pub span: Span,
@@ -190,7 +190,7 @@ pub(crate) struct UnallowedOpInConstContext {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_unallowed_heap_allocations, code = "E0010")]
+#[diag(const_eval_unallowed_heap_allocations, code = E0010)]
 pub(crate) struct UnallowedHeapAllocations {
     #[primary_span]
     #[label]
@@ -201,7 +201,7 @@ pub(crate) struct UnallowedHeapAllocations {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_unallowed_inline_asm, code = "E0015")]
+#[diag(const_eval_unallowed_inline_asm, code = E0015)]
 pub(crate) struct UnallowedInlineAsm {
     #[primary_span]
     pub span: Span,
@@ -209,7 +209,7 @@ pub(crate) struct UnallowedInlineAsm {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_interior_mutable_data_refer, code = "E0492")]
+#[diag(const_eval_interior_mutable_data_refer, code = E0492)]
 pub(crate) struct InteriorMutableDataRefer {
     #[primary_span]
     #[label]
@@ -274,7 +274,7 @@ pub struct RawBytesNote {
 // FIXME(fee1-dead) do not use stringly typed `ConstContext`
 
 #[derive(Diagnostic)]
-#[diag(const_eval_match_eq_non_const, code = "E0015")]
+#[diag(const_eval_match_eq_non_const, code = E0015)]
 #[note]
 pub struct NonConstMatchEq<'tcx> {
     #[primary_span]
@@ -284,7 +284,7 @@ pub struct NonConstMatchEq<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_for_loop_into_iter_non_const, code = "E0015")]
+#[diag(const_eval_for_loop_into_iter_non_const, code = E0015)]
 pub struct NonConstForLoopIntoIter<'tcx> {
     #[primary_span]
     pub span: Span,
@@ -293,7 +293,7 @@ pub struct NonConstForLoopIntoIter<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_question_branch_non_const, code = "E0015")]
+#[diag(const_eval_question_branch_non_const, code = E0015)]
 pub struct NonConstQuestionBranch<'tcx> {
     #[primary_span]
     pub span: Span,
@@ -302,7 +302,7 @@ pub struct NonConstQuestionBranch<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_question_from_residual_non_const, code = "E0015")]
+#[diag(const_eval_question_from_residual_non_const, code = E0015)]
 pub struct NonConstQuestionFromResidual<'tcx> {
     #[primary_span]
     pub span: Span,
@@ -311,7 +311,7 @@ pub struct NonConstQuestionFromResidual<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_try_block_from_output_non_const, code = "E0015")]
+#[diag(const_eval_try_block_from_output_non_const, code = E0015)]
 pub struct NonConstTryBlockFromOutput<'tcx> {
     #[primary_span]
     pub span: Span,
@@ -320,7 +320,7 @@ pub struct NonConstTryBlockFromOutput<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_await_non_const, code = "E0015")]
+#[diag(const_eval_await_non_const, code = E0015)]
 pub struct NonConstAwait<'tcx> {
     #[primary_span]
     pub span: Span,
@@ -329,7 +329,7 @@ pub struct NonConstAwait<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_closure_non_const, code = "E0015")]
+#[diag(const_eval_closure_non_const, code = E0015)]
 pub struct NonConstClosure {
     #[primary_span]
     pub span: Span,
@@ -362,7 +362,7 @@ pub struct ConsiderDereferencing {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_operator_non_const, code = "E0015")]
+#[diag(const_eval_operator_non_const, code = E0015)]
 pub struct NonConstOperator {
     #[primary_span]
     pub span: Span,
@@ -372,7 +372,7 @@ pub struct NonConstOperator {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_deref_coercion_non_const, code = "E0015")]
+#[diag(const_eval_deref_coercion_non_const, code = E0015)]
 #[note]
 pub struct NonConstDerefCoercion<'tcx> {
     #[primary_span]
@@ -385,7 +385,7 @@ pub struct NonConstDerefCoercion<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_live_drop, code = "E0493")]
+#[diag(const_eval_live_drop, code = E0493)]
 pub struct LiveDrop<'tcx> {
     #[primary_span]
     #[label]
@@ -397,7 +397,7 @@ pub struct LiveDrop<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_error, code = "E0080")]
+#[diag(const_eval_error, code = E0080)]
 pub struct ConstEvalError {
     #[primary_span]
     pub span: Span,
@@ -423,7 +423,7 @@ pub struct NullaryIntrinsicError {
 }
 
 #[derive(Diagnostic)]
-#[diag(const_eval_undefined_behavior, code = "E0080")]
+#[diag(const_eval_undefined_behavior, code = E0080)]
 pub struct UndefinedBehavior {
     #[primary_span]
     pub span: Span,
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/ops.rs b/compiler/rustc_const_eval/src/transform/check_consts/ops.rs
index 39bc2b960e9..fb705d91977 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/ops.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/ops.rs
@@ -2,7 +2,7 @@
 
 use hir::def_id::LocalDefId;
 use hir::{ConstContext, LangItem};
-use rustc_errors::{error_code, DiagnosticBuilder};
+use rustc_errors::{codes::*, DiagnosticBuilder};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::TyCtxtInferExt;
@@ -372,7 +372,7 @@ fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> DiagnosticBuilder<
         ccx.dcx().create_err(errors::UnallowedHeapAllocations {
             span,
             kind: ccx.const_kind(),
-            teach: ccx.tcx.sess.teach(&error_code!(E0010)).then_some(()),
+            teach: ccx.tcx.sess.teach(E0010).then_some(()),
         })
     }
 }
@@ -434,14 +434,14 @@ fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> DiagnosticBuilder<
                 span,
                 opt_help: Some(()),
                 kind: ccx.const_kind(),
-                teach: ccx.tcx.sess.teach(&error_code!(E0492)).then_some(()),
+                teach: ccx.tcx.sess.teach(E0492).then_some(()),
             })
         } else {
             ccx.dcx().create_err(errors::InteriorMutableDataRefer {
                 span,
                 opt_help: None,
                 kind: ccx.const_kind(),
-                teach: ccx.tcx.sess.teach(&error_code!(E0492)).then_some(()),
+                teach: ccx.tcx.sess.teach(E0492).then_some(()),
             })
         }
     }
@@ -469,12 +469,12 @@ fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> DiagnosticBuilder<
             hir::BorrowKind::Raw => ccx.tcx.dcx().create_err(errors::UnallowedMutableRaw {
                 span,
                 kind: ccx.const_kind(),
-                teach: ccx.tcx.sess.teach(&error_code!(E0764)).then_some(()),
+                teach: ccx.tcx.sess.teach(E0764).then_some(()),
             }),
             hir::BorrowKind::Ref => ccx.dcx().create_err(errors::UnallowedMutableRefs {
                 span,
                 kind: ccx.const_kind(),
-                teach: ccx.tcx.sess.teach(&error_code!(E0764)).then_some(()),
+                teach: ccx.tcx.sess.teach(E0764).then_some(()),
             }),
         }
     }
@@ -588,7 +588,7 @@ fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> DiagnosticBuilder<
         ccx.dcx().create_err(errors::StaticAccessErr {
             span,
             kind: ccx.const_kind(),
-            teach: ccx.tcx.sess.teach(&error_code!(E0013)).then_some(()),
+            teach: ccx.tcx.sess.teach(E0013).then_some(()),
         })
     }
 }
diff --git a/compiler/rustc_driver_impl/Cargo.toml b/compiler/rustc_driver_impl/Cargo.toml
index 97a7dfef3b3..bfdd871455c 100644
--- a/compiler/rustc_driver_impl/Cargo.toml
+++ b/compiler/rustc_driver_impl/Cargo.toml
@@ -15,7 +15,6 @@ rustc_builtin_macros = { path = "../rustc_builtin_macros" }
 rustc_codegen_ssa = { path = "../rustc_codegen_ssa" }
 rustc_const_eval = { path = "../rustc_const_eval" }
 rustc_data_structures = { path = "../rustc_data_structures" }
-rustc_error_codes = { path = "../rustc_error_codes" }
 rustc_errors = { path = "../rustc_errors" }
 rustc_expand = { path = "../rustc_expand" }
 rustc_feature = { path = "../rustc_feature" }
diff --git a/compiler/rustc_driver_impl/src/lib.rs b/compiler/rustc_driver_impl/src/lib.rs
index 09e627fa7a3..5903c43ae98 100644
--- a/compiler/rustc_driver_impl/src/lib.rs
+++ b/compiler/rustc_driver_impl/src/lib.rs
@@ -23,9 +23,8 @@
 use rustc_data_structures::profiling::{
     get_resident_set_size, print_time_passes_entry, TimePassesFormat,
 };
-use rustc_errors::registry::{InvalidErrorCode, Registry};
-use rustc_errors::{markdown, ColorConfig};
-use rustc_errors::{DiagCtxt, ErrorGuaranteed, PResult};
+use rustc_errors::registry::Registry;
+use rustc_errors::{markdown, ColorConfig, DiagCtxt, ErrCode, ErrorGuaranteed, PResult};
 use rustc_feature::find_gated_cfg;
 use rustc_interface::util::{self, collect_crate_types, get_codegen_backend};
 use rustc_interface::{interface, Queries};
@@ -207,7 +206,7 @@ fn config(&mut self, config: &mut interface::Config) {
 }
 
 pub fn diagnostics_registry() -> Registry {
-    Registry::new(rustc_error_codes::DIAGNOSTICS)
+    Registry::new(rustc_errors::codes::DIAGNOSTICS)
 }
 
 /// This is the primary entry point for rustc.
@@ -535,37 +534,36 @@ pub enum Compilation {
 }
 
 fn handle_explain(early_dcx: &EarlyDiagCtxt, registry: Registry, code: &str, color: ColorConfig) {
+    // Allow "E0123" or "0123" form.
     let upper_cased_code = code.to_ascii_uppercase();
-    let normalised =
-        if upper_cased_code.starts_with('E') { upper_cased_code } else { format!("E{code:0>4}") };
-    match registry.try_find_description(&normalised) {
-        Ok(description) => {
-            let mut is_in_code_block = false;
-            let mut text = String::new();
-            // Slice off the leading newline and print.
-            for line in description.lines() {
-                let indent_level =
-                    line.find(|c: char| !c.is_whitespace()).unwrap_or_else(|| line.len());
-                let dedented_line = &line[indent_level..];
-                if dedented_line.starts_with("```") {
-                    is_in_code_block = !is_in_code_block;
-                    text.push_str(&line[..(indent_level + 3)]);
-                } else if is_in_code_block && dedented_line.starts_with("# ") {
-                    continue;
-                } else {
-                    text.push_str(line);
-                }
-                text.push('\n');
-            }
-            if io::stdout().is_terminal() {
-                show_md_content_with_pager(&text, color);
+    let start = if upper_cased_code.starts_with('E') { 1 } else { 0 };
+    if let Ok(code) = upper_cased_code[start..].parse::<u32>()
+        && let Ok(description) = registry.try_find_description(ErrCode::from_u32(code))
+    {
+        let mut is_in_code_block = false;
+        let mut text = String::new();
+        // Slice off the leading newline and print.
+        for line in description.lines() {
+            let indent_level =
+                line.find(|c: char| !c.is_whitespace()).unwrap_or_else(|| line.len());
+            let dedented_line = &line[indent_level..];
+            if dedented_line.starts_with("```") {
+                is_in_code_block = !is_in_code_block;
+                text.push_str(&line[..(indent_level + 3)]);
+            } else if is_in_code_block && dedented_line.starts_with("# ") {
+                continue;
             } else {
-                safe_print!("{text}");
+                text.push_str(line);
             }
+            text.push('\n');
         }
-        Err(InvalidErrorCode) => {
-            early_dcx.early_fatal(format!("{code} is not a valid error code"));
+        if io::stdout().is_terminal() {
+            show_md_content_with_pager(&text, color);
+        } else {
+            safe_print!("{text}");
         }
+    } else {
+        early_dcx.early_fatal(format!("{code} is not a valid error code"));
     }
 }
 
diff --git a/compiler/rustc_error_codes/src/error_codes.rs b/compiler/rustc_error_codes/src/error_codes.rs
deleted file mode 100644
index 9cd9ed54d41..00000000000
--- a/compiler/rustc_error_codes/src/error_codes.rs
+++ /dev/null
@@ -1,658 +0,0 @@
-// Error messages for EXXXX errors. Each message should start and end with a
-// new line, and be wrapped to 80 characters. In vim you can `:set tw=80` and
-// use `gq` to wrap paragraphs. Use `:set tw=0` to disable.
-//
-// /!\ IMPORTANT /!\
-//
-// Error messages' format must follow the RFC 1567 available here:
-// https://rust-lang.github.io/rfcs/1567-long-error-codes-explanation-normalization.html
-
-register_diagnostics! {
-E0001: include_str!("./error_codes/E0001.md"),
-E0002: include_str!("./error_codes/E0002.md"),
-E0004: include_str!("./error_codes/E0004.md"),
-E0005: include_str!("./error_codes/E0005.md"),
-E0007: include_str!("./error_codes/E0007.md"),
-E0009: include_str!("./error_codes/E0009.md"),
-E0010: include_str!("./error_codes/E0010.md"),
-E0013: include_str!("./error_codes/E0013.md"),
-E0014: include_str!("./error_codes/E0014.md"),
-E0015: include_str!("./error_codes/E0015.md"),
-E0023: include_str!("./error_codes/E0023.md"),
-E0025: include_str!("./error_codes/E0025.md"),
-E0026: include_str!("./error_codes/E0026.md"),
-E0027: include_str!("./error_codes/E0027.md"),
-E0029: include_str!("./error_codes/E0029.md"),
-E0030: include_str!("./error_codes/E0030.md"),
-E0033: include_str!("./error_codes/E0033.md"),
-E0034: include_str!("./error_codes/E0034.md"),
-E0038: include_str!("./error_codes/E0038.md"),
-E0040: include_str!("./error_codes/E0040.md"),
-E0044: include_str!("./error_codes/E0044.md"),
-E0045: include_str!("./error_codes/E0045.md"),
-E0046: include_str!("./error_codes/E0046.md"),
-E0049: include_str!("./error_codes/E0049.md"),
-E0050: include_str!("./error_codes/E0050.md"),
-E0053: include_str!("./error_codes/E0053.md"),
-E0054: include_str!("./error_codes/E0054.md"),
-E0055: include_str!("./error_codes/E0055.md"),
-E0057: include_str!("./error_codes/E0057.md"),
-E0059: include_str!("./error_codes/E0059.md"),
-E0060: include_str!("./error_codes/E0060.md"),
-E0061: include_str!("./error_codes/E0061.md"),
-E0062: include_str!("./error_codes/E0062.md"),
-E0063: include_str!("./error_codes/E0063.md"),
-E0067: include_str!("./error_codes/E0067.md"),
-E0069: include_str!("./error_codes/E0069.md"),
-E0070: include_str!("./error_codes/E0070.md"),
-E0071: include_str!("./error_codes/E0071.md"),
-E0072: include_str!("./error_codes/E0072.md"),
-E0073: include_str!("./error_codes/E0073.md"),
-E0074: include_str!("./error_codes/E0074.md"),
-E0075: include_str!("./error_codes/E0075.md"),
-E0076: include_str!("./error_codes/E0076.md"),
-E0077: include_str!("./error_codes/E0077.md"),
-E0080: include_str!("./error_codes/E0080.md"),
-E0081: include_str!("./error_codes/E0081.md"),
-E0084: include_str!("./error_codes/E0084.md"),
-E0087: include_str!("./error_codes/E0087.md"),
-E0088: include_str!("./error_codes/E0088.md"),
-E0089: include_str!("./error_codes/E0089.md"),
-E0090: include_str!("./error_codes/E0090.md"),
-E0091: include_str!("./error_codes/E0091.md"),
-E0092: include_str!("./error_codes/E0092.md"),
-E0093: include_str!("./error_codes/E0093.md"),
-E0094: include_str!("./error_codes/E0094.md"),
-E0106: include_str!("./error_codes/E0106.md"),
-E0107: include_str!("./error_codes/E0107.md"),
-E0109: include_str!("./error_codes/E0109.md"),
-E0110: include_str!("./error_codes/E0110.md"),
-E0116: include_str!("./error_codes/E0116.md"),
-E0117: include_str!("./error_codes/E0117.md"),
-E0118: include_str!("./error_codes/E0118.md"),
-E0119: include_str!("./error_codes/E0119.md"),
-E0120: include_str!("./error_codes/E0120.md"),
-E0121: include_str!("./error_codes/E0121.md"),
-E0124: include_str!("./error_codes/E0124.md"),
-E0128: include_str!("./error_codes/E0128.md"),
-E0130: include_str!("./error_codes/E0130.md"),
-E0131: include_str!("./error_codes/E0131.md"),
-E0132: include_str!("./error_codes/E0132.md"),
-E0133: include_str!("./error_codes/E0133.md"),
-E0136: include_str!("./error_codes/E0136.md"),
-E0137: include_str!("./error_codes/E0137.md"),
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-E0714: include_str!("./error_codes/E0714.md"),
-E0715: include_str!("./error_codes/E0715.md"),
-E0716: include_str!("./error_codes/E0716.md"),
-E0711: include_str!("./error_codes/E0711.md"),
-E0717: include_str!("./error_codes/E0717.md"),
-E0718: include_str!("./error_codes/E0718.md"),
-E0719: include_str!("./error_codes/E0719.md"),
-E0720: include_str!("./error_codes/E0720.md"),
-E0722: include_str!("./error_codes/E0722.md"),
-E0724: include_str!("./error_codes/E0724.md"),
-E0725: include_str!("./error_codes/E0725.md"),
-E0726: include_str!("./error_codes/E0726.md"),
-E0727: include_str!("./error_codes/E0727.md"),
-E0728: include_str!("./error_codes/E0728.md"),
-E0729: include_str!("./error_codes/E0729.md"),
-E0730: include_str!("./error_codes/E0730.md"),
-E0731: include_str!("./error_codes/E0731.md"),
-E0732: include_str!("./error_codes/E0732.md"),
-E0733: include_str!("./error_codes/E0733.md"),
-E0734: include_str!("./error_codes/E0734.md"),
-E0735: include_str!("./error_codes/E0735.md"),
-E0736: include_str!("./error_codes/E0736.md"),
-E0737: include_str!("./error_codes/E0737.md"),
-E0739: include_str!("./error_codes/E0739.md"),
-E0740: include_str!("./error_codes/E0740.md"),
-E0741: include_str!("./error_codes/E0741.md"),
-E0742: include_str!("./error_codes/E0742.md"),
-E0743: include_str!("./error_codes/E0743.md"),
-E0744: include_str!("./error_codes/E0744.md"),
-E0745: include_str!("./error_codes/E0745.md"),
-E0746: include_str!("./error_codes/E0746.md"),
-E0747: include_str!("./error_codes/E0747.md"),
-E0748: include_str!("./error_codes/E0748.md"),
-E0749: include_str!("./error_codes/E0749.md"),
-E0750: include_str!("./error_codes/E0750.md"),
-E0751: include_str!("./error_codes/E0751.md"),
-E0752: include_str!("./error_codes/E0752.md"),
-E0753: include_str!("./error_codes/E0753.md"),
-E0754: include_str!("./error_codes/E0754.md"),
-E0755: include_str!("./error_codes/E0755.md"),
-E0756: include_str!("./error_codes/E0756.md"),
-E0757: include_str!("./error_codes/E0757.md"),
-E0758: include_str!("./error_codes/E0758.md"),
-E0759: include_str!("./error_codes/E0759.md"),
-E0760: include_str!("./error_codes/E0760.md"),
-E0761: include_str!("./error_codes/E0761.md"),
-E0762: include_str!("./error_codes/E0762.md"),
-E0763: include_str!("./error_codes/E0763.md"),
-E0764: include_str!("./error_codes/E0764.md"),
-E0765: include_str!("./error_codes/E0765.md"),
-E0766: include_str!("./error_codes/E0766.md"),
-E0767: include_str!("./error_codes/E0767.md"),
-E0768: include_str!("./error_codes/E0768.md"),
-E0769: include_str!("./error_codes/E0769.md"),
-E0770: include_str!("./error_codes/E0770.md"),
-E0771: include_str!("./error_codes/E0771.md"),
-E0772: include_str!("./error_codes/E0772.md"),
-E0773: include_str!("./error_codes/E0773.md"),
-E0774: include_str!("./error_codes/E0774.md"),
-E0775: include_str!("./error_codes/E0775.md"),
-E0776: include_str!("./error_codes/E0776.md"),
-E0777: include_str!("./error_codes/E0777.md"),
-E0778: include_str!("./error_codes/E0778.md"),
-E0779: include_str!("./error_codes/E0779.md"),
-E0780: include_str!("./error_codes/E0780.md"),
-E0781: include_str!("./error_codes/E0781.md"),
-E0782: include_str!("./error_codes/E0782.md"),
-E0783: include_str!("./error_codes/E0783.md"),
-E0784: include_str!("./error_codes/E0784.md"),
-E0785: include_str!("./error_codes/E0785.md"),
-E0786: include_str!("./error_codes/E0786.md"),
-E0787: include_str!("./error_codes/E0787.md"),
-E0788: include_str!("./error_codes/E0788.md"),
-E0789: include_str!("./error_codes/E0789.md"),
-E0790: include_str!("./error_codes/E0790.md"),
-E0791: include_str!("./error_codes/E0791.md"),
-E0792: include_str!("./error_codes/E0792.md"),
-E0793: include_str!("./error_codes/E0793.md"),
-E0794: include_str!("./error_codes/E0794.md"),
-E0795: include_str!("./error_codes/E0795.md"),
-E0796: include_str!("./error_codes/E0796.md"),
-E0797: include_str!("./error_codes/E0797.md"),
-}
-
-// Undocumented removed error codes. Note that many removed error codes are kept in the list above
-// and marked as no-longer emitted with a note in the markdown file (see E0001 for an example).
-//  E0006, // merged with E0005
-//  E0008, // cannot bind by-move into a pattern guard
-//  E0019, // merged into E0015
-//  E0035, // merged into E0087/E0089
-//  E0036, // merged into E0087/E0089
-//  E0068,
-//  E0085,
-//  E0086,
-//  E0101, // replaced with E0282
-//  E0102, // replaced with E0282
-//  E0103,
-//  E0104,
-//  E0122, // bounds in type aliases are ignored, turned into proper lint
-//  E0123,
-//  E0127,
-//  E0129,
-//  E0134,
-//  E0135,
-//  E0141,
-//  E0153, // unused error code
-//  E0157, // unused error code
-//  E0159, // use of trait `{}` as struct constructor
-//  E0163, // merged into E0071
-//  E0167,
-//  E0168,
-//  E0172, // non-trait found in a type sum, moved to resolve
-//  E0173, // manual implementations of unboxed closure traits are experimental
-//  E0174,
-//  E0182, // merged into E0229
-//  E0187, // cannot infer the kind of the closure
-//  E0188, // can not cast an immutable reference to a mutable pointer
-//  E0189, // deprecated: can only cast a boxed pointer to a boxed object
-//  E0190, // deprecated: can only cast a &-pointer to an &-object
-//  E0194, // merged into E0403
-//  E0196, // cannot determine a type for this closure
-//  E0209, // builtin traits can only be implemented on structs or enums
-//  E0213, // associated types are not accepted in this context
-//  E0215, // angle-bracket notation is not stable with `Fn`
-//  E0216, // parenthetical notation is only stable with `Fn`
-//  E0217, // ambiguous associated type, defined in multiple supertraits
-//  E0218, // no associated type defined
-//  E0219, // associated type defined in higher-ranked supertrait
-//  E0233,
-//  E0234,
-//  E0235, // structure constructor specifies a structure of type but
-//  E0236, // no lang item for range syntax
-//  E0237, // no lang item for range syntax
-//  E0238, // parenthesized parameters may only be used with a trait
-//  E0239, // `next` method of `Iterator` trait has unexpected type
-//  E0240,
-//  E0241,
-//  E0242,
-//  E0245, // not a trait
-//  E0246, // invalid recursive type
-//  E0247,
-//  E0248, // value used as a type, now reported earlier during resolution
-//         // as E0412
-//  E0249,
-//  E0257,
-//  E0258,
-//  E0272, // on_unimplemented #0
-//  E0273, // on_unimplemented #1
-//  E0274, // on_unimplemented #2
-//  E0278, // requirement is not satisfied
-//  E0279,
-//  E0280, // changed to ICE
-//  E0285, // overflow evaluation builtin bounds
-//  E0296, // replaced with a generic attribute input check
-//  E0298, // cannot compare constants
-//  E0299, // mismatched types between arms
-//  E0300, // unexpanded macro
-//  E0304, // expected signed integer constant
-//  E0305, // expected constant
-//  E0313, // removed: found unreachable
-//  E0314, // closure outlives stack frame
-//  E0315, // cannot invoke closure outside of its lifetime
-//  E0319, // trait impls for defaulted traits allowed just for structs/enums
-//  E0372, // coherence not object safe
-//  E0385, // {} in an aliasable location
-//  E0402, // cannot use an outer type parameter in this context
-//  E0406, // merged into 420
-//  E0410, // merged into 408
-//  E0413, // merged into 530
-//  E0414, // merged into 530
-//  E0417, // merged into 532
-//  E0418, // merged into 532
-//  E0419, // merged into 531
-//  E0420, // merged into 532
-//  E0421, // merged into 531
-//  E0427, // merged into 530
-//  E0445, // merged into 446 and type privacy lints
-//  E0456, // plugin `..` is not available for triple `..`
-//  E0465, // removed: merged with E0464
-//  E0467, // removed
-//  E0470, // removed
-//  E0471, // constant evaluation error (in pattern)
-//  E0473, // dereference of reference outside its lifetime
-//  E0474, // captured variable `..` does not outlive the enclosing closure
-//  E0475, // index of slice outside its lifetime
-//  E0479, // the type `..` (provided as the value of a type parameter) is...
-//  E0480, // lifetime of method receiver does not outlive the method call
-//  E0481, // lifetime of function argument does not outlive the function call
-//  E0483, // lifetime of operand does not outlive the operation
-//  E0484, // reference is not valid at the time of borrow
-//  E0485, // automatically reference is not valid at the time of borrow
-//  E0486, // type of expression contains references that are not valid during..
-//  E0487, // unsafe use of destructor: destructor might be called while...
-//  E0488, // lifetime of variable does not enclose its declaration
-//  E0489, // type/lifetime parameter not in scope here
-//  E0490, // removed: unreachable
-//  E0526, // shuffle indices are not constant
-//  E0540, // multiple rustc_deprecated attributes
-//  E0548, // replaced with a generic attribute input check
-//  E0553, // multiple rustc_const_unstable attributes
-//  E0555, // replaced with a generic attribute input check
-//  E0558, // replaced with a generic attribute input check
-//  E0563, // cannot determine a type for this `impl Trait` removed in 6383de15
-//  E0564, // only named lifetimes are allowed in `impl Trait`,
-//         // but `{}` was found in the type `{}`
-//  E0598, // lifetime of {} is too short to guarantee its contents can be...
-//  E0611, // merged into E0616
-//  E0612, // merged into E0609
-//  E0613, // Removed (merged with E0609)
-//  E0629, // missing 'feature' (rustc_const_unstable)
-//  E0630, // rustc_const_unstable attribute must be paired with stable/unstable
-//         // attribute
-//  E0645, // trait aliases not finished
-//  E0694, // an unknown tool name found in scoped attributes
-//  E0702, // replaced with a generic attribute input check
-//  E0707, // multiple elided lifetimes used in arguments of `async fn`
-//  E0709, // multiple different lifetimes used in arguments of `async fn`
-//  E0721, // `await` keyword
-//  E0723, // unstable feature in `const` context
-//  E0738, // Removed; errored on `#[track_caller] fn`s in `extern "Rust" { ... }`.
-//  E0744, // merged into E0728
diff --git a/compiler/rustc_error_codes/src/lib.rs b/compiler/rustc_error_codes/src/lib.rs
index dd281811636..5b2766618fc 100644
--- a/compiler/rustc_error_codes/src/lib.rs
+++ b/compiler/rustc_error_codes/src/lib.rs
@@ -1,19 +1,679 @@
+//! This library is used to gather all error codes into one place, to make
+//! their maintenance easier.
+
 #![allow(internal_features)]
 #![feature(rustdoc_internals)]
 #![doc(rust_logo)]
 #![deny(rustdoc::invalid_codeblock_attributes)]
 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]
-//! This library is used to gather all error codes into one place,
-//! the goal being to make their maintenance easier.
 
-macro_rules! register_diagnostics {
-    ($($ecode:ident: $message:expr,)*) => (
-        pub static DIAGNOSTICS: &[(&str, &str)] = &[
-            $( (stringify!($ecode), $message), )*
-        ];
+// This higher-order macro defines the error codes that are in use. It is used
+// in the `rustc_errors` crate. Removed error codes are listed in the comment
+// below.
+//
+// /!\ IMPORTANT /!\
+//
+// Error code explanation are defined in `error_codes/EXXXX.md` files. They must follow the RFC
+// 1567 available here:
+// https://rust-lang.github.io/rfcs/1567-long-error-codes-explanation-normalization.html
+//
+// Also, the contents of this macro is checked by tidy (in `check_error_codes_docs`). If you change
+// the macro syntax you will need to change tidy as well.
+//
+// Both columns are necessary because it's not possible in Rust to create a new identifier such as
+// `E0123` from an integer literal such as `0123`, unfortunately.
+#[macro_export]
+macro_rules! error_codes {
+    ($macro:path) => (
+        $macro!(
+E0001: 0001,
+E0002: 0002,
+E0004: 0004,
+E0005: 0005,
+E0007: 0007,
+E0009: 0009,
+E0010: 0010,
+E0013: 0013,
+E0014: 0014,
+E0015: 0015,
+E0023: 0023,
+E0025: 0025,
+E0026: 0026,
+E0027: 0027,
+E0029: 0029,
+E0030: 0030,
+E0033: 0033,
+E0034: 0034,
+E0038: 0038,
+E0040: 0040,
+E0044: 0044,
+E0045: 0045,
+E0046: 0046,
+E0049: 0049,
+E0050: 0050,
+E0053: 0053,
+E0054: 0054,
+E0055: 0055,
+E0057: 0057,
+E0059: 0059,
+E0060: 0060,
+E0061: 0061,
+E0062: 0062,
+E0063: 0063,
+E0067: 0067,
+E0069: 0069,
+E0070: 0070,
+E0071: 0071,
+E0072: 0072,
+E0073: 0073,
+E0074: 0074,
+E0075: 0075,
+E0076: 0076,
+E0077: 0077,
+E0080: 0080,
+E0081: 0081,
+E0084: 0084,
+E0087: 0087,
+E0088: 0088,
+E0089: 0089,
+E0090: 0090,
+E0091: 0091,
+E0092: 0092,
+E0093: 0093,
+E0094: 0094,
+E0106: 0106,
+E0107: 0107,
+E0109: 0109,
+E0110: 0110,
+E0116: 0116,
+E0117: 0117,
+E0118: 0118,
+E0119: 0119,
+E0120: 0120,
+E0121: 0121,
+E0124: 0124,
+E0128: 0128,
+E0130: 0130,
+E0131: 0131,
+E0132: 0132,
+E0133: 0133,
+E0136: 0136,
+E0137: 0137,
+E0138: 0138,
+E0139: 0139,
+E0152: 0152,
+E0154: 0154,
+E0158: 0158,
+E0161: 0161,
+E0162: 0162,
+E0164: 0164,
+E0165: 0165,
+E0170: 0170,
+E0178: 0178,
+E0183: 0183,
+E0184: 0184,
+E0185: 0185,
+E0186: 0186,
+E0191: 0191,
+E0192: 0192,
+E0193: 0193,
+E0195: 0195,
+E0197: 0197,
+E0198: 0198,
+E0199: 0199,
+E0200: 0200,
+E0201: 0201,
+E0203: 0203,
+E0204: 0204,
+E0205: 0205,
+E0206: 0206,
+E0207: 0207,
+E0208: 0208,
+E0210: 0210,
+E0211: 0211,
+E0212: 0212,
+E0214: 0214,
+E0220: 0220,
+E0221: 0221,
+E0222: 0222,
+E0223: 0223,
+E0224: 0224,
+E0225: 0225,
+E0226: 0226,
+E0227: 0227,
+E0228: 0228,
+E0229: 0229,
+E0230: 0230,
+E0231: 0231,
+E0232: 0232,
+E0243: 0243,
+E0244: 0244,
+E0251: 0251,
+E0252: 0252,
+E0253: 0253,
+E0254: 0254,
+E0255: 0255,
+E0256: 0256,
+E0259: 0259,
+E0260: 0260,
+E0261: 0261,
+E0262: 0262,
+E0263: 0263,
+E0264: 0264,
+E0267: 0267,
+E0268: 0268,
+E0271: 0271,
+E0275: 0275,
+E0276: 0276,
+E0277: 0277,
+E0281: 0281,
+E0282: 0282,
+E0283: 0283,
+E0284: 0284,
+E0297: 0297,
+E0301: 0301,
+E0302: 0302,
+E0303: 0303,
+E0307: 0307,
+E0308: 0308,
+E0309: 0309,
+E0310: 0310,
+E0311: 0311,
+E0312: 0312,
+E0316: 0316,
+E0317: 0317,
+E0320: 0320,
+E0321: 0321,
+E0322: 0322,
+E0323: 0323,
+E0324: 0324,
+E0325: 0325,
+E0326: 0326,
+E0328: 0328,
+E0329: 0329,
+E0364: 0364,
+E0365: 0365,
+E0366: 0366,
+E0367: 0367,
+E0368: 0368,
+E0369: 0369,
+E0370: 0370,
+E0371: 0371,
+E0373: 0373,
+E0374: 0374,
+E0375: 0375,
+E0376: 0376,
+E0377: 0377,
+E0378: 0378,
+E0379: 0379,
+E0380: 0380,
+E0381: 0381,
+E0382: 0382,
+E0383: 0383,
+E0384: 0384,
+E0386: 0386,
+E0387: 0387,
+E0388: 0388,
+E0389: 0389,
+E0390: 0390,
+E0391: 0391,
+E0392: 0392,
+E0393: 0393,
+E0398: 0398,
+E0399: 0399,
+E0401: 0401,
+E0403: 0403,
+E0404: 0404,
+E0405: 0405,
+E0407: 0407,
+E0408: 0408,
+E0409: 0409,
+E0411: 0411,
+E0412: 0412,
+E0415: 0415,
+E0416: 0416,
+E0422: 0422,
+E0423: 0423,
+E0424: 0424,
+E0425: 0425,
+E0426: 0426,
+E0428: 0428,
+E0429: 0429,
+E0430: 0430,
+E0431: 0431,
+E0432: 0432,
+E0433: 0433,
+E0434: 0434,
+E0435: 0435,
+E0436: 0436,
+E0437: 0437,
+E0438: 0438,
+E0439: 0439,
+E0445: 0445,
+E0446: 0446,
+E0447: 0447,
+E0448: 0448,
+E0449: 0449,
+E0451: 0451,
+E0452: 0452,
+E0453: 0453,
+E0454: 0454,
+E0455: 0455,
+E0457: 0457,
+E0458: 0458,
+E0459: 0459,
+E0460: 0460,
+E0461: 0461,
+E0462: 0462,
+E0463: 0463,
+E0464: 0464,
+E0466: 0466,
+E0468: 0468,
+E0469: 0469,
+E0472: 0472,
+E0476: 0476,
+E0477: 0477,
+E0478: 0478,
+E0482: 0482,
+E0491: 0491,
+E0492: 0492,
+E0493: 0493,
+E0495: 0495,
+E0496: 0496,
+E0497: 0497,
+E0498: 0498,
+E0499: 0499,
+E0500: 0500,
+E0501: 0501,
+E0502: 0502,
+E0503: 0503,
+E0504: 0504,
+E0505: 0505,
+E0506: 0506,
+E0507: 0507,
+E0508: 0508,
+E0509: 0509,
+E0510: 0510,
+E0511: 0511,
+E0512: 0512,
+E0514: 0514,
+E0515: 0515,
+E0516: 0516,
+E0517: 0517,
+E0518: 0518,
+E0519: 0519,
+E0520: 0520,
+E0521: 0521,
+E0522: 0522,
+E0523: 0523,
+E0524: 0524,
+E0525: 0525,
+E0527: 0527,
+E0528: 0528,
+E0529: 0529,
+E0530: 0530,
+E0531: 0531,
+E0532: 0532,
+E0533: 0533,
+E0534: 0534,
+E0535: 0535,
+E0536: 0536,
+E0537: 0537,
+E0538: 0538,
+E0539: 0539,
+E0541: 0541,
+E0542: 0542,
+E0543: 0543,
+E0544: 0544,
+E0545: 0545,
+E0546: 0546,
+E0547: 0547,
+E0549: 0549,
+E0550: 0550,
+E0551: 0551,
+E0552: 0552,
+E0554: 0554,
+E0556: 0556,
+E0557: 0557,
+E0559: 0559,
+E0560: 0560,
+E0561: 0561,
+E0562: 0562,
+E0565: 0565,
+E0566: 0566,
+E0567: 0567,
+E0568: 0568,
+E0569: 0569,
+E0570: 0570,
+E0571: 0571,
+E0572: 0572,
+E0573: 0573,
+E0574: 0574,
+E0575: 0575,
+E0576: 0576,
+E0577: 0577,
+E0578: 0578,
+E0579: 0579,
+E0580: 0580,
+E0581: 0581,
+E0582: 0582,
+E0583: 0583,
+E0584: 0584,
+E0585: 0585,
+E0586: 0586,
+E0587: 0587,
+E0588: 0588,
+E0589: 0589,
+E0590: 0590,
+E0591: 0591,
+E0592: 0592,
+E0593: 0593,
+E0594: 0594,
+E0595: 0595,
+E0596: 0596,
+E0597: 0597,
+E0599: 0599,
+E0600: 0600,
+E0601: 0601,
+E0602: 0602,
+E0603: 0603,
+E0604: 0604,
+E0605: 0605,
+E0606: 0606,
+E0607: 0607,
+E0608: 0608,
+E0609: 0609,
+E0610: 0610,
+E0614: 0614,
+E0615: 0615,
+E0616: 0616,
+E0617: 0617,
+E0618: 0618,
+E0619: 0619,
+E0620: 0620,
+E0621: 0621,
+E0622: 0622,
+E0623: 0623,
+E0624: 0624,
+E0625: 0625,
+E0626: 0626,
+E0627: 0627,
+E0628: 0628,
+E0631: 0631,
+E0632: 0632,
+E0633: 0633,
+E0634: 0634,
+E0635: 0635,
+E0636: 0636,
+E0637: 0637,
+E0638: 0638,
+E0639: 0639,
+E0640: 0640,
+E0641: 0641,
+E0642: 0642,
+E0643: 0643,
+E0644: 0644,
+E0646: 0646,
+E0647: 0647,
+E0648: 0648,
+E0657: 0657,
+E0658: 0658,
+E0659: 0659,
+E0660: 0660,
+E0661: 0661,
+E0662: 0662,
+E0663: 0663,
+E0664: 0664,
+E0665: 0665,
+E0666: 0666,
+E0667: 0667,
+E0668: 0668,
+E0669: 0669,
+E0670: 0670,
+E0671: 0671,
+E0687: 0687,
+E0688: 0688,
+E0689: 0689,
+E0690: 0690,
+E0691: 0691,
+E0692: 0692,
+E0693: 0693,
+E0695: 0695,
+E0696: 0696,
+E0697: 0697,
+E0698: 0698,
+E0699: 0699,
+E0700: 0700,
+E0701: 0701,
+E0703: 0703,
+E0704: 0704,
+E0705: 0705,
+E0706: 0706,
+E0708: 0708,
+E0710: 0710,
+E0712: 0712,
+E0713: 0713,
+E0714: 0714,
+E0715: 0715,
+E0716: 0716,
+E0711: 0711,
+E0717: 0717,
+E0718: 0718,
+E0719: 0719,
+E0720: 0720,
+E0722: 0722,
+E0724: 0724,
+E0725: 0725,
+E0726: 0726,
+E0727: 0727,
+E0728: 0728,
+E0729: 0729,
+E0730: 0730,
+E0731: 0731,
+E0732: 0732,
+E0733: 0733,
+E0734: 0734,
+E0735: 0735,
+E0736: 0736,
+E0737: 0737,
+E0739: 0739,
+E0740: 0740,
+E0741: 0741,
+E0742: 0742,
+E0743: 0743,
+E0744: 0744,
+E0745: 0745,
+E0746: 0746,
+E0747: 0747,
+E0748: 0748,
+E0749: 0749,
+E0750: 0750,
+E0751: 0751,
+E0752: 0752,
+E0753: 0753,
+E0754: 0754,
+E0755: 0755,
+E0756: 0756,
+E0757: 0757,
+E0758: 0758,
+E0759: 0759,
+E0760: 0760,
+E0761: 0761,
+E0762: 0762,
+E0763: 0763,
+E0764: 0764,
+E0765: 0765,
+E0766: 0766,
+E0767: 0767,
+E0768: 0768,
+E0769: 0769,
+E0770: 0770,
+E0771: 0771,
+E0772: 0772,
+E0773: 0773,
+E0774: 0774,
+E0775: 0775,
+E0776: 0776,
+E0777: 0777,
+E0778: 0778,
+E0779: 0779,
+E0780: 0780,
+E0781: 0781,
+E0782: 0782,
+E0783: 0783,
+E0784: 0784,
+E0785: 0785,
+E0786: 0786,
+E0787: 0787,
+E0788: 0788,
+E0789: 0789,
+E0790: 0790,
+E0791: 0791,
+E0792: 0792,
+E0793: 0793,
+E0794: 0794,
+E0795: 0795,
+E0796: 0796,
+E0797: 0797,
+        );
     )
 }
 
-mod error_codes;
-pub use error_codes::DIAGNOSTICS;
+// Undocumented removed error codes. Note that many removed error codes are kept in the list above
+// and marked as no-longer emitted with a note in the markdown file (see E0001 for an example).
+//  E0006, // merged with E0005
+//  E0008, // cannot bind by-move into a pattern guard
+//  E0019, // merged into E0015
+//  E0035, // merged into E0087/E0089
+//  E0036, // merged into E0087/E0089
+//  E0068,
+//  E0085,
+//  E0086,
+//  E0101, // replaced with E0282
+//  E0102, // replaced with E0282
+//  E0103,
+//  E0104,
+//  E0122, // bounds in type aliases are ignored, turned into proper lint
+//  E0123,
+//  E0127,
+//  E0129,
+//  E0134,
+//  E0135,
+//  E0141,
+//  E0153, // unused error code
+//  E0157, // unused error code
+//  E0159, // use of trait `{}` as struct constructor
+//  E0163, // merged into E0071
+//  E0167,
+//  E0168,
+//  E0172, // non-trait found in a type sum, moved to resolve
+//  E0173, // manual implementations of unboxed closure traits are experimental
+//  E0174,
+//  E0182, // merged into E0229
+//  E0187, // cannot infer the kind of the closure
+//  E0188, // can not cast an immutable reference to a mutable pointer
+//  E0189, // deprecated: can only cast a boxed pointer to a boxed object
+//  E0190, // deprecated: can only cast a &-pointer to an &-object
+//  E0194, // merged into E0403
+//  E0196, // cannot determine a type for this closure
+//  E0209, // builtin traits can only be implemented on structs or enums
+//  E0213, // associated types are not accepted in this context
+//  E0215, // angle-bracket notation is not stable with `Fn`
+//  E0216, // parenthetical notation is only stable with `Fn`
+//  E0217, // ambiguous associated type, defined in multiple supertraits
+//  E0218, // no associated type defined
+//  E0219, // associated type defined in higher-ranked supertrait
+//  E0233,
+//  E0234,
+//  E0235, // structure constructor specifies a structure of type but
+//  E0236, // no lang item for range syntax
+//  E0237, // no lang item for range syntax
+//  E0238, // parenthesized parameters may only be used with a trait
+//  E0239, // `next` method of `Iterator` trait has unexpected type
+//  E0240,
+//  E0241,
+//  E0242,
+//  E0245, // not a trait
+//  E0246, // invalid recursive type
+//  E0247,
+//  E0248, // value used as a type, now reported earlier during resolution
+//         // as E0412
+//  E0249,
+//  E0257,
+//  E0258,
+//  E0272, // on_unimplemented #0
+//  E0273, // on_unimplemented #1
+//  E0274, // on_unimplemented #2
+//  E0278, // requirement is not satisfied
+//  E0279,
+//  E0280, // changed to ICE
+//  E0285, // overflow evaluation builtin bounds
+//  E0296, // replaced with a generic attribute input check
+//  E0298, // cannot compare constants
+//  E0299, // mismatched types between arms
+//  E0300, // unexpanded macro
+//  E0304, // expected signed integer constant
+//  E0305, // expected constant
+//  E0313, // removed: found unreachable
+//  E0314, // closure outlives stack frame
+//  E0315, // cannot invoke closure outside of its lifetime
+//  E0319, // trait impls for defaulted traits allowed just for structs/enums
+//  E0372, // coherence not object safe
+//  E0385, // {} in an aliasable location
+//  E0402, // cannot use an outer type parameter in this context
+//  E0406, // merged into 420
+//  E0410, // merged into 408
+//  E0413, // merged into 530
+//  E0414, // merged into 530
+//  E0417, // merged into 532
+//  E0418, // merged into 532
+//  E0419, // merged into 531
+//  E0420, // merged into 532
+//  E0421, // merged into 531
+//  E0427, // merged into 530
+//  E0445, // merged into 446 and type privacy lints
+//  E0456, // plugin `..` is not available for triple `..`
+//  E0465, // removed: merged with E0464
+//  E0467, // removed
+//  E0470, // removed
+//  E0471, // constant evaluation error (in pattern)
+//  E0473, // dereference of reference outside its lifetime
+//  E0474, // captured variable `..` does not outlive the enclosing closure
+//  E0475, // index of slice outside its lifetime
+//  E0479, // the type `..` (provided as the value of a type parameter) is...
+//  E0480, // lifetime of method receiver does not outlive the method call
+//  E0481, // lifetime of function argument does not outlive the function call
+//  E0483, // lifetime of operand does not outlive the operation
+//  E0484, // reference is not valid at the time of borrow
+//  E0485, // automatically reference is not valid at the time of borrow
+//  E0486, // type of expression contains references that are not valid during..
+//  E0487, // unsafe use of destructor: destructor might be called while...
+//  E0488, // lifetime of variable does not enclose its declaration
+//  E0489, // type/lifetime parameter not in scope here
+//  E0490, // removed: unreachable
+//  E0526, // shuffle indices are not constant
+//  E0540, // multiple rustc_deprecated attributes
+//  E0548, // replaced with a generic attribute input check
+//  E0553, // multiple rustc_const_unstable attributes
+//  E0555, // replaced with a generic attribute input check
+//  E0558, // replaced with a generic attribute input check
+//  E0563, // cannot determine a type for this `impl Trait` removed in 6383de15
+//  E0564, // only named lifetimes are allowed in `impl Trait`,
+//         // but `{}` was found in the type `{}`
+//  E0598, // lifetime of {} is too short to guarantee its contents can be...
+//  E0611, // merged into E0616
+//  E0612, // merged into E0609
+//  E0613, // Removed (merged with E0609)
+//  E0629, // missing 'feature' (rustc_const_unstable)
+//  E0630, // rustc_const_unstable attribute must be paired with stable/unstable
+//         // attribute
+//  E0645, // trait aliases not finished
+//  E0694, // an unknown tool name found in scoped attributes
+//  E0702, // replaced with a generic attribute input check
+//  E0707, // multiple elided lifetimes used in arguments of `async fn`
+//  E0709, // multiple different lifetimes used in arguments of `async fn`
+//  E0721, // `await` keyword
+//  E0723, // unstable feature in `const` context
+//  E0738, // Removed; errored on `#[track_caller] fn`s in `extern "Rust" { ... }`.
+//  E0744, // merged into E0728
diff --git a/compiler/rustc_errors/Cargo.toml b/compiler/rustc_errors/Cargo.toml
index 0c1fcecb571..a2d1fd2a924 100644
--- a/compiler/rustc_errors/Cargo.toml
+++ b/compiler/rustc_errors/Cargo.toml
@@ -10,9 +10,11 @@ derive_setters = "0.1.6"
 rustc_ast = { path = "../rustc_ast" }
 rustc_ast_pretty = { path = "../rustc_ast_pretty" }
 rustc_data_structures = { path = "../rustc_data_structures" }
+rustc_error_codes = { path = "../rustc_error_codes" }
 rustc_error_messages = { path = "../rustc_error_messages" }
 rustc_fluent_macro = { path = "../rustc_fluent_macro" }
 rustc_hir = { path = "../rustc_hir" }
+rustc_index = { path = "../rustc_index" }
 rustc_lint_defs = { path = "../rustc_lint_defs" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_serialize = { path = "../rustc_serialize" }
diff --git a/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs b/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
index f0699a56f98..949f52ef6b5 100644
--- a/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
+++ b/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
@@ -9,8 +9,8 @@
 use crate::snippet::Line;
 use crate::translation::{to_fluent_args, Translate};
 use crate::{
-    CodeSuggestion, Diagnostic, DiagnosticMessage, Emitter, FluentBundle, LazyFallbackBundle,
-    Level, MultiSpan, Style, SubDiagnostic,
+    CodeSuggestion, Diagnostic, DiagnosticMessage, Emitter, ErrCode, FluentBundle,
+    LazyFallbackBundle, Level, MultiSpan, Style, SubDiagnostic,
 };
 use annotate_snippets::{Annotation, AnnotationType, Renderer, Slice, Snippet, SourceAnnotation};
 use rustc_data_structures::sync::Lrc;
@@ -127,7 +127,7 @@ fn emit_messages_default(
         level: &Level,
         messages: &[(DiagnosticMessage, Style)],
         args: &FluentArgs<'_>,
-        code: &Option<String>,
+        code: &Option<ErrCode>,
         msp: &MultiSpan,
         _children: &[SubDiagnostic],
         _suggestions: &[CodeSuggestion],
@@ -178,6 +178,7 @@ fn emit_messages_default(
                         .collect::<Vec<Owned>>()
                 })
                 .collect();
+            let code = code.map(|code| code.to_string());
             let snippet = Snippet {
                 title: Some(Annotation {
                     label: Some(&message),
diff --git a/compiler/rustc_errors/src/codes.rs b/compiler/rustc_errors/src/codes.rs
new file mode 100644
index 00000000000..947cf27ca79
--- /dev/null
+++ b/compiler/rustc_errors/src/codes.rs
@@ -0,0 +1,39 @@
+//! This module defines the following.
+//! - The `ErrCode` type.
+//! - A constant for every error code, with a name like `E0123`.
+//! - A static table `DIAGNOSTICS` pairing every error code constant with its
+//!   long description text.
+
+use std::fmt;
+
+rustc_index::newtype_index! {
+    #[max = 9999] // Because all error codes have four digits.
+    #[orderable]
+    #[encodable]
+    #[debug_format = "ErrCode({})"]
+    pub struct ErrCode {}
+}
+
+impl fmt::Display for ErrCode {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "E{:04}", self.as_u32())
+    }
+}
+
+macro_rules! define_error_code_constants_and_diagnostics_table {
+    ($($name:ident: $num:literal,)*) => (
+        $(
+            pub const $name: $crate::ErrCode = $crate::ErrCode::from_u32($num);
+        )*
+        pub static DIAGNOSTICS: &[($crate::ErrCode, &str)] = &[
+            $( (
+                $name,
+                include_str!(
+                    concat!("../../rustc_error_codes/src/error_codes/", stringify!($name), ".md")
+                )
+            ), )*
+        ];
+    )
+}
+
+rustc_error_codes::error_codes!(define_error_code_constants_and_diagnostics_table);
diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index 4934bc2450c..8a32e29ddc9 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@@ -1,7 +1,8 @@
 use crate::snippet::Style;
 use crate::{
-    CodeSuggestion, DelayedBugKind, DiagnosticBuilder, DiagnosticMessage, EmissionGuarantee, Level,
-    MultiSpan, SubdiagnosticMessage, Substitution, SubstitutionPart, SuggestionStyle,
+    CodeSuggestion, DelayedBugKind, DiagnosticBuilder, DiagnosticMessage, EmissionGuarantee,
+    ErrCode, Level, MultiSpan, SubdiagnosticMessage, Substitution, SubstitutionPart,
+    SuggestionStyle,
 };
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
 use rustc_error_messages::fluent_value_from_str_list_sep_by_and;
@@ -104,7 +105,7 @@ pub struct Diagnostic {
     pub(crate) level: Level,
 
     pub messages: Vec<(DiagnosticMessage, Style)>,
-    pub code: Option<String>,
+    pub code: Option<ErrCode>,
     pub span: MultiSpan,
     pub children: Vec<SubDiagnostic>,
     pub suggestions: Result<Vec<CodeSuggestion>, SuggestionsDisabled>,
@@ -893,8 +894,8 @@ pub fn is_lint(&mut self, name: String, has_future_breakage: bool) -> &mut Self
         self
     }
 
-    pub fn code(&mut self, s: String) -> &mut Self {
-        self.code = Some(s);
+    pub fn code(&mut self, code: ErrCode) -> &mut Self {
+        self.code = Some(code);
         self
     }
 
@@ -903,8 +904,8 @@ pub fn clear_code(&mut self) -> &mut Self {
         self
     }
 
-    pub fn get_code(&self) -> Option<&str> {
-        self.code.as_deref()
+    pub fn get_code(&self) -> Option<ErrCode> {
+        self.code
     }
 
     pub fn primary_message(&mut self, msg: impl Into<DiagnosticMessage>) -> &mut Self {
@@ -990,7 +991,7 @@ fn keys(
         &Level,
         &[(DiagnosticMessage, Style)],
         Vec<(&Cow<'static, str>, &DiagnosticArgValue<'static>)>,
-        &Option<String>,
+        &Option<ErrCode>,
         &Option<IsLint>,
         &MultiSpan,
         &Result<Vec<CodeSuggestion>, SuggestionsDisabled>,
diff --git a/compiler/rustc_errors/src/diagnostic_builder.rs b/compiler/rustc_errors/src/diagnostic_builder.rs
index 87e2d295c7f..8bfb1816486 100644
--- a/compiler/rustc_errors/src/diagnostic_builder.rs
+++ b/compiler/rustc_errors/src/diagnostic_builder.rs
@@ -1,7 +1,7 @@
 use crate::diagnostic::IntoDiagnosticArg;
 use crate::{DiagCtxt, Level, MultiSpan, StashKey};
 use crate::{
-    Diagnostic, DiagnosticMessage, DiagnosticStyledString, ErrorGuaranteed, ExplicitBug,
+    Diagnostic, DiagnosticMessage, DiagnosticStyledString, ErrCode, ErrorGuaranteed, ExplicitBug,
     SubdiagnosticMessage,
 };
 use rustc_lint_defs::Applicability;
@@ -399,7 +399,7 @@ pub fn delay_as_bug(mut self) -> G::EmitResult {
         name: String, has_future_breakage: bool,
     ));
     forward!((code, with_code)(
-        s: String,
+        code: ErrCode,
     ));
     forward!((arg, with_arg)(
         name: impl Into<Cow<'static, str>>, arg: impl IntoDiagnosticArg,
@@ -439,12 +439,7 @@ fn drop(&mut self) {
 
 #[macro_export]
 macro_rules! struct_span_code_err {
-    ($dcx:expr, $span:expr, $code:ident, $($message:tt)*) => ({
-        $dcx.struct_span_err($span, format!($($message)*)).with_code($crate::error_code!($code))
+    ($dcx:expr, $span:expr, $code:expr, $($message:tt)*) => ({
+        $dcx.struct_span_err($span, format!($($message)*)).with_code($code)
     })
 }
-
-#[macro_export]
-macro_rules! error_code {
-    ($code:ident) => {{ stringify!($code).to_owned() }};
-}
diff --git a/compiler/rustc_errors/src/diagnostic_impls.rs b/compiler/rustc_errors/src/diagnostic_impls.rs
index d58d05095cd..df3fd4af4b4 100644
--- a/compiler/rustc_errors/src/diagnostic_impls.rs
+++ b/compiler/rustc_errors/src/diagnostic_impls.rs
@@ -1,7 +1,7 @@
 use crate::diagnostic::DiagnosticLocation;
 use crate::{fluent_generated as fluent, AddToDiagnostic};
 use crate::{
-    DiagCtxt, DiagnosticArgValue, DiagnosticBuilder, EmissionGuarantee, IntoDiagnostic,
+    DiagCtxt, DiagnosticArgValue, DiagnosticBuilder, EmissionGuarantee, ErrCode, IntoDiagnostic,
     IntoDiagnosticArg, Level,
 };
 use rustc_ast as ast;
@@ -93,6 +93,7 @@ fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
     &TargetTriple,
     SplitDebuginfo,
     ExitStatus,
+    ErrCode,
 );
 
 into_diagnostic_arg_for_number!(i8, u8, i16, u16, i32, u32, i64, u64, i128, u128, isize, usize);
diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index 23efdaea0eb..9f76c1dd248 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -17,8 +17,8 @@
 use crate::translation::{to_fluent_args, Translate};
 use crate::{
     diagnostic::DiagnosticLocation, CodeSuggestion, DiagCtxt, Diagnostic, DiagnosticMessage,
-    FluentBundle, LazyFallbackBundle, Level, MultiSpan, SubDiagnostic, SubstitutionHighlight,
-    SuggestionStyle, TerminalUrl,
+    ErrCode, FluentBundle, LazyFallbackBundle, Level, MultiSpan, SubDiagnostic,
+    SubstitutionHighlight, SuggestionStyle, TerminalUrl,
 };
 use rustc_lint_defs::pluralize;
 
@@ -1309,7 +1309,7 @@ fn emit_messages_default_inner(
         msp: &MultiSpan,
         msgs: &[(DiagnosticMessage, Style)],
         args: &FluentArgs<'_>,
-        code: &Option<String>,
+        code: &Option<ErrCode>,
         level: &Level,
         max_line_num_len: usize,
         is_secondary: bool,
@@ -1340,9 +1340,9 @@ fn emit_messages_default_inner(
                 buffer.append(0, "[", Style::Level(*level));
                 let code = if let TerminalUrl::Yes = self.terminal_url {
                     let path = "https://doc.rust-lang.org/error_codes";
-                    Cow::Owned(format!("\x1b]8;;{path}/{code}.html\x07{code}\x1b]8;;\x07"))
+                    format!("\x1b]8;;{path}/{code}.html\x07{code}\x1b]8;;\x07")
                 } else {
-                    Cow::Borrowed(code)
+                    code.to_string()
                 };
                 buffer.append(0, &code, Style::Level(*level));
                 buffer.append(0, "]", Style::Level(*level));
@@ -2076,7 +2076,7 @@ fn emit_messages_default(
         level: &Level,
         messages: &[(DiagnosticMessage, Style)],
         args: &FluentArgs<'_>,
-        code: &Option<String>,
+        code: &Option<ErrCode>,
         span: &MultiSpan,
         children: &[SubDiagnostic],
         suggestions: &[CodeSuggestion],
diff --git a/compiler/rustc_errors/src/json.rs b/compiler/rustc_errors/src/json.rs
index 51b064f4c61..6f922998279 100644
--- a/compiler/rustc_errors/src/json.rs
+++ b/compiler/rustc_errors/src/json.rs
@@ -400,10 +400,10 @@ fn reset(&mut self) -> io::Result<()> {
 
         let translated_message = je.translate_messages(&diag.messages, &args);
 
-        let code = if let Some(code) = &diag.code {
+        let code = if let Some(code) = diag.code {
             Some(DiagnosticCode {
                 code: code.to_string(),
-                explanation: je.registry.as_ref().unwrap().try_find_description(&code).ok(),
+                explanation: je.registry.as_ref().unwrap().try_find_description(code).ok(),
             })
         } else if let Some(IsLint { name, .. }) = &diag.is_lint {
             Some(DiagnosticCode { code: name.to_string(), explanation: None })
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index a64ad2beb6c..6d9208341a5 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -14,6 +14,7 @@
 #![feature(error_reporter)]
 #![feature(extract_if)]
 #![feature(let_chains)]
+#![feature(min_specialization)]
 #![feature(negative_impls)]
 #![feature(never_type)]
 #![feature(rustc_attrs)]
@@ -30,6 +31,7 @@
 
 extern crate self as rustc_errors;
 
+pub use codes::*;
 pub use diagnostic::{
     AddToDiagnostic, DecorateLint, Diagnostic, DiagnosticArg, DiagnosticArgValue,
     DiagnosticStyledString, IntoDiagnosticArg, SubDiagnostic,
@@ -78,6 +80,7 @@
 use Level::*;
 
 pub mod annotate_snippet_emitter_writer;
+pub mod codes;
 mod diagnostic;
 mod diagnostic_builder;
 mod diagnostic_impls;
@@ -446,10 +449,10 @@ struct DiagCtxtInner {
     /// This set contains the code of all emitted diagnostics to avoid
     /// emitting the same diagnostic with extended help (`--teach`) twice, which
     /// would be unnecessary repetition.
-    taught_diagnostics: FxHashSet<String>,
+    taught_diagnostics: FxHashSet<ErrCode>,
 
     /// Used to suggest rustc --explain `<error code>`
-    emitted_diagnostic_codes: FxIndexSet<String>,
+    emitted_diagnostic_codes: FxIndexSet<ErrCode>,
 
     /// This set contains a hash of every diagnostic that has been emitted by
     /// this `DiagCtxt`. These hashes is used to avoid emitting the same error
@@ -1004,9 +1007,9 @@ pub fn print_error_count(&self, registry: &Registry) {
             let mut error_codes = inner
                 .emitted_diagnostic_codes
                 .iter()
-                .filter_map(|code| {
+                .filter_map(|&code| {
                     if registry.try_find_description(code).is_ok().clone() {
-                        Some(code.clone())
+                        Some(code.to_string())
                     } else {
                         None
                     }
@@ -1052,8 +1055,8 @@ pub fn abort_if_errors(&self) {
     ///
     /// Used to suppress emitting the same error multiple times with extended explanation when
     /// calling `-Zteach`.
-    pub fn must_teach(&self, code: &str) -> bool {
-        self.inner.borrow_mut().taught_diagnostics.insert(code.to_string())
+    pub fn must_teach(&self, code: ErrCode) -> bool {
+        self.inner.borrow_mut().taught_diagnostics.insert(code)
     }
 
     pub fn force_print_diagnostic(&self, db: Diagnostic) {
@@ -1313,8 +1316,8 @@ fn emit_diagnostic(&mut self, mut diagnostic: Diagnostic) -> Option<ErrorGuarant
 
         let mut guaranteed = None;
         (*TRACK_DIAGNOSTIC)(diagnostic, &mut |mut diagnostic| {
-            if let Some(ref code) = diagnostic.code {
-                self.emitted_diagnostic_codes.insert(code.clone());
+            if let Some(code) = diagnostic.code {
+                self.emitted_diagnostic_codes.insert(code);
             }
 
             let already_emitted = {
diff --git a/compiler/rustc_errors/src/registry.rs b/compiler/rustc_errors/src/registry.rs
index f26d8e7ebdc..8834d04d971 100644
--- a/compiler/rustc_errors/src/registry.rs
+++ b/compiler/rustc_errors/src/registry.rs
@@ -1,3 +1,4 @@
+use crate::ErrCode;
 use rustc_data_structures::fx::FxHashMap;
 
 #[derive(Debug)]
@@ -5,17 +6,17 @@
 
 #[derive(Clone)]
 pub struct Registry {
-    long_descriptions: FxHashMap<&'static str, &'static str>,
+    long_descriptions: FxHashMap<ErrCode, &'static str>,
 }
 
 impl Registry {
-    pub fn new(long_descriptions: &[(&'static str, &'static str)]) -> Registry {
+    pub fn new(long_descriptions: &[(ErrCode, &'static str)]) -> Registry {
         Registry { long_descriptions: long_descriptions.iter().copied().collect() }
     }
 
     /// Returns `InvalidErrorCode` if the code requested does not exist in the
     /// registry.
-    pub fn try_find_description(&self, code: &str) -> Result<&'static str, InvalidErrorCode> {
-        self.long_descriptions.get(code).copied().ok_or(InvalidErrorCode)
+    pub fn try_find_description(&self, code: ErrCode) -> Result<&'static str, InvalidErrorCode> {
+        self.long_descriptions.get(&code).copied().ok_or(InvalidErrorCode)
     }
 }
diff --git a/compiler/rustc_expand/src/errors.rs b/compiler/rustc_expand/src/errors.rs
index 4a1c00f0104..2584ff62e98 100644
--- a/compiler/rustc_expand/src/errors.rs
+++ b/compiler/rustc_expand/src/errors.rs
@@ -1,4 +1,5 @@
 use rustc_ast::ast;
+use rustc_errors::codes::*;
 use rustc_macros::Diagnostic;
 use rustc_session::Limit;
 use rustc_span::symbol::{Ident, MacroRulesNormalizedIdent};
@@ -175,7 +176,7 @@ pub(crate) struct TakesNoArguments<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(expand_feature_removed, code = "E0557")]
+#[diag(expand_feature_removed, code = E0557)]
 pub(crate) struct FeatureRemoved<'a> {
     #[primary_span]
     #[label]
@@ -191,7 +192,7 @@ pub(crate) struct FeatureRemovedReason<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(expand_feature_not_allowed, code = "E0725")]
+#[diag(expand_feature_not_allowed, code = E0725)]
 pub(crate) struct FeatureNotAllowed {
     #[primary_span]
     pub span: Span,
@@ -210,7 +211,7 @@ pub(crate) struct RecursionLimitReached<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(expand_malformed_feature_attribute, code = "E0556")]
+#[diag(expand_malformed_feature_attribute, code = E0556)]
 pub(crate) struct MalformedFeatureAttribute {
     #[primary_span]
     pub span: Span,
@@ -347,7 +348,7 @@ pub(crate) struct ModuleInBlockName {
 }
 
 #[derive(Diagnostic)]
-#[diag(expand_module_file_not_found, code = "E0583")]
+#[diag(expand_module_file_not_found, code = E0583)]
 #[help]
 #[note]
 pub(crate) struct ModuleFileNotFound {
@@ -359,7 +360,7 @@ pub(crate) struct ModuleFileNotFound {
 }
 
 #[derive(Diagnostic)]
-#[diag(expand_module_multiple_candidates, code = "E0761")]
+#[diag(expand_module_multiple_candidates, code = E0761)]
 #[help]
 pub(crate) struct ModuleMultipleCandidates {
     #[primary_span]
diff --git a/compiler/rustc_hir_analysis/src/astconv/bounds.rs b/compiler/rustc_hir_analysis/src/astconv/bounds.rs
index 3aad510f366..c22daad334f 100644
--- a/compiler/rustc_hir_analysis/src/astconv/bounds.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/bounds.rs
@@ -1,5 +1,5 @@
 use rustc_data_structures::fx::FxHashMap;
-use rustc_errors::struct_span_code_err;
+use rustc_errors::{codes::*, struct_span_code_err};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{DefId, LocalDefId};
diff --git a/compiler/rustc_hir_analysis/src/astconv/errors.rs b/compiler/rustc_hir_analysis/src/astconv/errors.rs
index bfe88df4e1a..5e9076243f8 100644
--- a/compiler/rustc_hir_analysis/src/astconv/errors.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/errors.rs
@@ -7,7 +7,9 @@
 use crate::traits::error_reporting::report_object_safety_error;
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap, FxIndexSet};
 use rustc_data_structures::unord::UnordMap;
-use rustc_errors::{pluralize, struct_span_code_err, Applicability, Diagnostic, ErrorGuaranteed};
+use rustc_errors::{
+    codes::*, pluralize, struct_span_code_err, Applicability, Diagnostic, ErrorGuaranteed,
+};
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_infer::traits::FulfillmentError;
diff --git a/compiler/rustc_hir_analysis/src/astconv/generics.rs b/compiler/rustc_hir_analysis/src/astconv/generics.rs
index 4284758b117..30b10446afc 100644
--- a/compiler/rustc_hir_analysis/src/astconv/generics.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/generics.rs
@@ -5,7 +5,9 @@
 };
 use crate::structured_errors::{GenericArgsInfo, StructuredDiagnostic, WrongNumberOfGenericArgs};
 use rustc_ast::ast::ParamKindOrd;
-use rustc_errors::{struct_span_code_err, Applicability, Diagnostic, ErrorGuaranteed, MultiSpan};
+use rustc_errors::{
+    codes::*, struct_span_code_err, Applicability, Diagnostic, ErrorGuaranteed, MultiSpan,
+};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::DefId;
diff --git a/compiler/rustc_hir_analysis/src/astconv/lint.rs b/compiler/rustc_hir_analysis/src/astconv/lint.rs
index 33e782abc68..98cd8a085ba 100644
--- a/compiler/rustc_hir_analysis/src/astconv/lint.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/lint.rs
@@ -1,5 +1,5 @@
 use rustc_ast::TraitObjectSyntax;
-use rustc_errors::{Diagnostic, StashKey};
+use rustc_errors::{codes::*, Diagnostic, StashKey};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_lint_defs::{builtin::BARE_TRAIT_OBJECTS, Applicability};
diff --git a/compiler/rustc_hir_analysis/src/astconv/mod.rs b/compiler/rustc_hir_analysis/src/astconv/mod.rs
index 7c97c2a1a6f..2dec0ab4355 100644
--- a/compiler/rustc_hir_analysis/src/astconv/mod.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/mod.rs
@@ -18,8 +18,8 @@
 use rustc_ast::TraitObjectSyntax;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::{
-    error_code, struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder,
-    ErrorGuaranteed, FatalError, MultiSpan,
+    codes::*, struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
+    FatalError, MultiSpan,
 };
 use rustc_hir as hir;
 use rustc_hir::def::{CtorOf, DefKind, Namespace, Res};
@@ -1072,9 +1072,9 @@ fn one_bound_for_assoc_item<I>(
                 if let Some(binding) = binding
                     && let ConvertedBindingKind::Equality(_) = binding.kind
                 {
-                    error_code!(E0222)
+                    E0222
                 } else {
-                    error_code!(E0221)
+                    E0221
                 },
             );
 
@@ -1630,7 +1630,7 @@ fn check_assoc_ty(
             let reported = tcx
                 .dcx()
                 .struct_span_err(span, msg)
-                .with_code(rustc_errors::error_code!(E0624))
+                .with_code(E0624)
                 .with_span_label(span, format!("private {kind}"))
                 .with_span_label(def_span, format!("{kind} defined here"))
                 .emit();
diff --git a/compiler/rustc_hir_analysis/src/astconv/object_safety.rs b/compiler/rustc_hir_analysis/src/astconv/object_safety.rs
index 5f35f75c77b..2d85ad5789e 100644
--- a/compiler/rustc_hir_analysis/src/astconv/object_safety.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/object_safety.rs
@@ -2,7 +2,7 @@
 use crate::bounds::Bounds;
 use crate::errors::TraitObjectDeclaredWithNoTraits;
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
-use rustc_errors::struct_span_code_err;
+use rustc_errors::{codes::*, struct_span_code_err};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::DefId;
diff --git a/compiler/rustc_hir_analysis/src/check/check.rs b/compiler/rustc_hir_analysis/src/check/check.rs
index c63bafcdcd4..2fe3499e8e6 100644
--- a/compiler/rustc_hir_analysis/src/check/check.rs
+++ b/compiler/rustc_hir_analysis/src/check/check.rs
@@ -5,7 +5,7 @@
 use super::compare_impl_item::{compare_impl_method, compare_impl_ty};
 use super::*;
 use rustc_attr as attr;
-use rustc_errors::{ErrorGuaranteed, MultiSpan};
+use rustc_errors::{codes::*, ErrorGuaranteed, MultiSpan};
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, DefKind};
 use rustc_hir::def_id::{DefId, LocalDefId};
diff --git a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
index 57829d9d418..479421af77f 100644
--- a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
+++ b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
@@ -2,7 +2,7 @@
 use crate::errors::LifetimesOrBoundsMismatchOnTrait;
 use hir::def_id::{DefId, DefIdMap, LocalDefId};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
-use rustc_errors::{pluralize, struct_span_code_err, Applicability, ErrorGuaranteed};
+use rustc_errors::{codes::*, pluralize, struct_span_code_err, Applicability, ErrorGuaranteed};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::intravisit;
@@ -1382,7 +1382,7 @@ fn compare_number_of_generics<'tcx>(
                     kind = kind,
                 ),
             );
-            err.code("E0049".into());
+            err.code(E0049);
 
             let msg =
                 format!("expected {trait_count} {kind} parameter{}", pluralize!(trait_count),);
diff --git a/compiler/rustc_hir_analysis/src/check/dropck.rs b/compiler/rustc_hir_analysis/src/check/dropck.rs
index 3275a81c3dd..9fe95487bb9 100644
--- a/compiler/rustc_hir_analysis/src/check/dropck.rs
+++ b/compiler/rustc_hir_analysis/src/check/dropck.rs
@@ -2,7 +2,7 @@
 //
 // We don't do any drop checking during hir typeck.
 use rustc_data_structures::fx::FxHashSet;
-use rustc_errors::{struct_span_code_err, ErrorGuaranteed};
+use rustc_errors::{codes::*, struct_span_code_err, ErrorGuaranteed};
 use rustc_infer::infer::outlives::env::OutlivesEnvironment;
 use rustc_infer::infer::{RegionResolutionError, TyCtxtInferExt};
 use rustc_middle::ty::util::CheckRegions;
diff --git a/compiler/rustc_hir_analysis/src/check/intrinsic.rs b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
index 60e4403c1c7..2d0d6611444 100644
--- a/compiler/rustc_hir_analysis/src/check/intrinsic.rs
+++ b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
@@ -8,7 +8,7 @@
 };
 
 use hir::def_id::DefId;
-use rustc_errors::{struct_span_code_err, DiagnosticMessage};
+use rustc_errors::{codes::*, struct_span_code_err, DiagnosticMessage};
 use rustc_hir as hir;
 use rustc_middle::traits::{ObligationCause, ObligationCauseCode};
 use rustc_middle::ty::{self, Ty, TyCtxt};
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
index 70213ee0614..0978a5e6596 100644
--- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs
+++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -4,7 +4,7 @@
 use rustc_ast as ast;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
 use rustc_errors::{
-    pluralize, struct_span_code_err, Applicability, DiagnosticBuilder, ErrorGuaranteed,
+    codes::*, pluralize, struct_span_code_err, Applicability, DiagnosticBuilder, ErrorGuaranteed,
 };
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId, LocalModDefId};
diff --git a/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs b/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs
index 63ea0272014..951440d6a2d 100644
--- a/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs
@@ -1,5 +1,5 @@
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
-use rustc_errors::struct_span_code_err;
+use rustc_errors::{codes::*, struct_span_code_err};
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
diff --git a/compiler/rustc_hir_analysis/src/coherence/mod.rs b/compiler/rustc_hir_analysis/src/coherence/mod.rs
index dafa899ef24..8cf1f2c9407 100644
--- a/compiler/rustc_hir_analysis/src/coherence/mod.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/mod.rs
@@ -6,7 +6,7 @@
 // mappings. That mapping code resides here.
 
 use crate::errors;
-use rustc_errors::{error_code, struct_span_code_err};
+use rustc_errors::{codes::*, struct_span_code_err};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{self, TyCtxt, TypeVisitableExt};
@@ -61,7 +61,7 @@ fn enforce_trait_manually_implementable(
         // Maintain explicit error code for `Unsize`, since it has a useful
         // explanation about using `CoerceUnsized` instead.
         if Some(trait_def_id) == tcx.lang_items().unsize_trait() {
-            err.code(error_code!(E0328));
+            err.code(E0328);
         }
 
         return Err(err.emit());
diff --git a/compiler/rustc_hir_analysis/src/coherence/unsafety.rs b/compiler/rustc_hir_analysis/src/coherence/unsafety.rs
index e4c407af53f..e3b5c724cde 100644
--- a/compiler/rustc_hir_analysis/src/coherence/unsafety.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/unsafety.rs
@@ -1,7 +1,7 @@
 //! Unsafety checker: every impl either implements a trait defined in this
 //! crate or pertains to a type defined in this crate.
 
-use rustc_errors::struct_span_code_err;
+use rustc_errors::{codes::*, struct_span_code_err};
 use rustc_hir as hir;
 use rustc_hir::Unsafety;
 use rustc_middle::ty::TyCtxt;
diff --git a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
index a857e01f4fa..97d792e49ae 100644
--- a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
+++ b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
@@ -8,7 +8,7 @@
 
 use rustc_ast::walk_list;
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
-use rustc_errors::struct_span_code_err;
+use rustc_errors::{codes::*, struct_span_code_err};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::LocalDefId;
diff --git a/compiler/rustc_hir_analysis/src/errors.rs b/compiler/rustc_hir_analysis/src/errors.rs
index f14390b77c6..e5871276d64 100644
--- a/compiler/rustc_hir_analysis/src/errors.rs
+++ b/compiler/rustc_hir_analysis/src/errors.rs
@@ -2,8 +2,8 @@
 
 use crate::fluent_generated as fluent;
 use rustc_errors::{
-    error_code, Applicability, DiagCtxt, DiagnosticBuilder, EmissionGuarantee, IntoDiagnostic,
-    Level, MultiSpan,
+    codes::*, Applicability, DiagCtxt, DiagnosticBuilder, EmissionGuarantee, IntoDiagnostic, Level,
+    MultiSpan,
 };
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
 use rustc_middle::ty::Ty;
@@ -52,7 +52,7 @@ pub struct AssocKindMismatchWrapInBracesSugg {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_assoc_item_not_found, code = "E0220")]
+#[diag(hir_analysis_assoc_item_not_found, code = E0220)]
 pub struct AssocItemNotFound<'a> {
     #[primary_span]
     pub span: Span,
@@ -122,7 +122,7 @@ pub enum AssocItemNotFoundSugg<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_unrecognized_atomic_operation, code = "E0092")]
+#[diag(hir_analysis_unrecognized_atomic_operation, code = E0092)]
 pub struct UnrecognizedAtomicOperation<'a> {
     #[primary_span]
     #[label]
@@ -131,7 +131,7 @@ pub struct UnrecognizedAtomicOperation<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_wrong_number_of_generic_arguments_to_intrinsic, code = "E0094")]
+#[diag(hir_analysis_wrong_number_of_generic_arguments_to_intrinsic, code = E0094)]
 pub struct WrongNumberOfGenericArgumentsToIntrinsic<'a> {
     #[primary_span]
     #[label]
@@ -142,7 +142,7 @@ pub struct WrongNumberOfGenericArgumentsToIntrinsic<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_unrecognized_intrinsic_function, code = "E0093")]
+#[diag(hir_analysis_unrecognized_intrinsic_function, code = E0093)]
 pub struct UnrecognizedIntrinsicFunction {
     #[primary_span]
     #[label]
@@ -151,7 +151,7 @@ pub struct UnrecognizedIntrinsicFunction {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_lifetimes_or_bounds_mismatch_on_trait, code = "E0195")]
+#[diag(hir_analysis_lifetimes_or_bounds_mismatch_on_trait, code = E0195)]
 pub struct LifetimesOrBoundsMismatchOnTrait {
     #[primary_span]
     #[label]
@@ -178,7 +178,7 @@ pub struct AsyncTraitImplShouldBeAsync {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_drop_impl_on_wrong_item, code = "E0120")]
+#[diag(hir_analysis_drop_impl_on_wrong_item, code = E0120)]
 pub struct DropImplOnWrongItem {
     #[primary_span]
     #[label]
@@ -186,7 +186,7 @@ pub struct DropImplOnWrongItem {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_field_already_declared, code = "E0124")]
+#[diag(hir_analysis_field_already_declared, code = E0124)]
 pub struct FieldAlreadyDeclared {
     pub field_name: Ident,
     #[primary_span]
@@ -197,7 +197,7 @@ pub struct FieldAlreadyDeclared {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_copy_impl_on_type_with_dtor, code = "E0184")]
+#[diag(hir_analysis_copy_impl_on_type_with_dtor, code = E0184)]
 pub struct CopyImplOnTypeWithDtor {
     #[primary_span]
     #[label]
@@ -205,14 +205,14 @@ pub struct CopyImplOnTypeWithDtor {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_multiple_relaxed_default_bounds, code = "E0203")]
+#[diag(hir_analysis_multiple_relaxed_default_bounds, code = E0203)]
 pub struct MultipleRelaxedDefaultBounds {
     #[primary_span]
     pub spans: Vec<Span>,
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_copy_impl_on_non_adt, code = "E0206")]
+#[diag(hir_analysis_copy_impl_on_non_adt, code = E0206)]
 pub struct CopyImplOnNonAdt {
     #[primary_span]
     #[label]
@@ -228,7 +228,7 @@ pub struct ConstParamTyImplOnNonAdt {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_trait_object_declared_with_no_traits, code = "E0224")]
+#[diag(hir_analysis_trait_object_declared_with_no_traits, code = E0224)]
 pub struct TraitObjectDeclaredWithNoTraits {
     #[primary_span]
     pub span: Span,
@@ -237,14 +237,14 @@ pub struct TraitObjectDeclaredWithNoTraits {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_ambiguous_lifetime_bound, code = "E0227")]
+#[diag(hir_analysis_ambiguous_lifetime_bound, code = E0227)]
 pub struct AmbiguousLifetimeBound {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_assoc_type_binding_not_allowed, code = "E0229")]
+#[diag(hir_analysis_assoc_type_binding_not_allowed, code = E0229)]
 pub struct AssocTypeBindingNotAllowed {
     #[primary_span]
     #[label]
@@ -264,7 +264,7 @@ pub struct ParenthesizedFnTraitExpansion {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_typeof_reserved_keyword_used, code = "E0516")]
+#[diag(hir_analysis_typeof_reserved_keyword_used, code = E0516)]
 pub struct TypeofReservedKeywordUsed<'tcx> {
     pub ty: Ty<'tcx>,
     #[primary_span]
@@ -275,7 +275,7 @@ pub struct TypeofReservedKeywordUsed<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_value_of_associated_struct_already_specified, code = "E0719")]
+#[diag(hir_analysis_value_of_associated_struct_already_specified, code = E0719)]
 pub struct ValueOfAssociatedStructAlreadySpecified {
     #[primary_span]
     #[label]
@@ -320,7 +320,7 @@ impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for MissingTypeParams {
     fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> DiagnosticBuilder<'a, G> {
         let mut err = DiagnosticBuilder::new(dcx, level, fluent::hir_analysis_missing_type_params);
         err.span(self.span);
-        err.code(error_code!(E0393));
+        err.code(E0393);
         err.arg("parameterCount", self.missing_type_params.len());
         err.arg(
             "parameters",
@@ -373,7 +373,7 @@ fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> DiagnosticBuilder<'
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_manual_implementation, code = "E0183")]
+#[diag(hir_analysis_manual_implementation, code = E0183)]
 #[help]
 pub struct ManualImplementation {
     #[primary_span]
@@ -421,7 +421,7 @@ pub struct SelfInImplSelf {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_linkage_type, code = "E0791")]
+#[diag(hir_analysis_linkage_type, code = E0791)]
 pub(crate) struct LinkageType {
     #[primary_span]
     pub span: Span,
@@ -429,7 +429,7 @@ pub(crate) struct LinkageType {
 
 #[derive(Diagnostic)]
 #[help]
-#[diag(hir_analysis_auto_deref_reached_recursion_limit, code = "E0055")]
+#[diag(hir_analysis_auto_deref_reached_recursion_limit, code = E0055)]
 pub struct AutoDerefReachedRecursionLimit<'a> {
     #[primary_span]
     #[label]
@@ -440,7 +440,7 @@ pub struct AutoDerefReachedRecursionLimit<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_where_clause_on_main, code = "E0646")]
+#[diag(hir_analysis_where_clause_on_main, code = E0646)]
 pub(crate) struct WhereClauseOnMain {
     #[primary_span]
     pub span: Span,
@@ -485,7 +485,7 @@ pub(crate) struct StartTargetFeature {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_start_not_async, code = "E0752")]
+#[diag(hir_analysis_start_not_async, code = E0752)]
 pub(crate) struct StartAsync {
     #[primary_span]
     #[label]
@@ -493,7 +493,7 @@ pub(crate) struct StartAsync {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_start_function_where, code = "E0647")]
+#[diag(hir_analysis_start_function_where, code = E0647)]
 pub(crate) struct StartFunctionWhere {
     #[primary_span]
     #[label]
@@ -501,7 +501,7 @@ pub(crate) struct StartFunctionWhere {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_start_function_parameters, code = "E0132")]
+#[diag(hir_analysis_start_function_parameters, code = E0132)]
 pub(crate) struct StartFunctionParameters {
     #[primary_span]
     #[label]
@@ -509,14 +509,14 @@ pub(crate) struct StartFunctionParameters {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_main_function_return_type_generic, code = "E0131")]
+#[diag(hir_analysis_main_function_return_type_generic, code = E0131)]
 pub(crate) struct MainFunctionReturnTypeGeneric {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_main_function_async, code = "E0752")]
+#[diag(hir_analysis_main_function_async, code = E0752)]
 pub(crate) struct MainFunctionAsync {
     #[primary_span]
     pub span: Span,
@@ -525,7 +525,7 @@ pub(crate) struct MainFunctionAsync {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_main_function_generic_parameters, code = "E0131")]
+#[diag(hir_analysis_main_function_generic_parameters, code = E0131)]
 pub(crate) struct MainFunctionGenericParameters {
     #[primary_span]
     pub span: Span,
@@ -534,7 +534,7 @@ pub(crate) struct MainFunctionGenericParameters {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_variadic_function_compatible_convention, code = "E0045")]
+#[diag(hir_analysis_variadic_function_compatible_convention, code = E0045)]
 pub(crate) struct VariadicFunctionCompatibleConvention<'a> {
     #[primary_span]
     #[label]
@@ -587,7 +587,7 @@ pub(crate) struct TypeOf<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_pass_to_variadic_function, code = "E0617")]
+#[diag(hir_analysis_pass_to_variadic_function, code = E0617)]
 pub(crate) struct PassToVariadicFunction<'tcx, 'a> {
     #[primary_span]
     pub span: Span,
@@ -601,7 +601,7 @@ pub(crate) struct PassToVariadicFunction<'tcx, 'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_cast_thin_pointer_to_fat_pointer, code = "E0607")]
+#[diag(hir_analysis_cast_thin_pointer_to_fat_pointer, code = E0607)]
 pub(crate) struct CastThinPointerToFatPointer<'tcx> {
     #[primary_span]
     pub span: Span,
@@ -610,7 +610,7 @@ pub(crate) struct CastThinPointerToFatPointer<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_invalid_union_field, code = "E0740")]
+#[diag(hir_analysis_invalid_union_field, code = E0740)]
 pub(crate) struct InvalidUnionField {
     #[primary_span]
     pub field_span: Span,
@@ -649,7 +649,7 @@ pub(crate) struct ReturnTypeNotationEqualityBound {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_placeholder_not_allowed_item_signatures, code = "E0121")]
+#[diag(hir_analysis_placeholder_not_allowed_item_signatures, code = E0121)]
 pub(crate) struct PlaceholderNotAllowedItemSignatures {
     #[primary_span]
     #[label]
@@ -658,7 +658,7 @@ pub(crate) struct PlaceholderNotAllowedItemSignatures {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_associated_type_trait_uninferred_generic_params, code = "E0212")]
+#[diag(hir_analysis_associated_type_trait_uninferred_generic_params, code = E0212)]
 pub(crate) struct AssociatedTypeTraitUninferredGenericParams {
     #[primary_span]
     pub span: Span,
@@ -684,7 +684,7 @@ pub(crate) struct AssociatedTypeTraitUninferredGenericParamsMultipartSuggestion
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_enum_discriminant_overflowed, code = "E0370")]
+#[diag(hir_analysis_enum_discriminant_overflowed, code = E0370)]
 #[note]
 pub(crate) struct EnumDiscriminantOverflowed {
     #[primary_span]
@@ -774,7 +774,7 @@ pub(crate) struct SIMDFFIHighlyExperimental {
 
 #[derive(Diagnostic)]
 pub enum ImplNotMarkedDefault {
-    #[diag(hir_analysis_impl_not_marked_default, code = "E0520")]
+    #[diag(hir_analysis_impl_not_marked_default, code = E0520)]
     #[note]
     Ok {
         #[primary_span]
@@ -784,7 +784,7 @@ pub enum ImplNotMarkedDefault {
         ok_label: Span,
         ident: Symbol,
     },
-    #[diag(hir_analysis_impl_not_marked_default_err, code = "E0520")]
+    #[diag(hir_analysis_impl_not_marked_default_err, code = E0520)]
     #[note]
     Err {
         #[primary_span]
@@ -795,7 +795,7 @@ pub enum ImplNotMarkedDefault {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_missing_trait_item, code = "E0046")]
+#[diag(hir_analysis_missing_trait_item, code = E0046)]
 pub(crate) struct MissingTraitItem {
     #[primary_span]
     #[label]
@@ -846,7 +846,7 @@ pub(crate) struct MissingTraitItemSuggestionNone {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_missing_one_of_trait_item, code = "E0046")]
+#[diag(hir_analysis_missing_one_of_trait_item, code = E0046)]
 pub(crate) struct MissingOneOfTraitItem {
     #[primary_span]
     #[label]
@@ -857,7 +857,7 @@ pub(crate) struct MissingOneOfTraitItem {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_missing_trait_item_unstable, code = "E0046")]
+#[diag(hir_analysis_missing_trait_item_unstable, code = E0046)]
 #[note]
 pub(crate) struct MissingTraitItemUnstable {
     #[primary_span]
@@ -872,7 +872,7 @@ pub(crate) struct MissingTraitItemUnstable {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_transparent_enum_variant, code = "E0731")]
+#[diag(hir_analysis_transparent_enum_variant, code = E0731)]
 pub(crate) struct TransparentEnumVariant {
     #[primary_span]
     #[label]
@@ -886,7 +886,7 @@ pub(crate) struct TransparentEnumVariant {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_transparent_non_zero_sized_enum, code = "E0690")]
+#[diag(hir_analysis_transparent_non_zero_sized_enum, code = E0690)]
 pub(crate) struct TransparentNonZeroSizedEnum<'a> {
     #[primary_span]
     #[label]
@@ -898,7 +898,7 @@ pub(crate) struct TransparentNonZeroSizedEnum<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_transparent_non_zero_sized, code = "E0690")]
+#[diag(hir_analysis_transparent_non_zero_sized, code = E0690)]
 pub(crate) struct TransparentNonZeroSized<'a> {
     #[primary_span]
     #[label]
@@ -1045,7 +1045,7 @@ pub(crate) struct ReturnPositionImplTraitInTraitRefined<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_inherent_ty_outside, code = "E0390")]
+#[diag(hir_analysis_inherent_ty_outside, code = E0390)]
 #[help]
 pub struct InherentTyOutside {
     #[primary_span]
@@ -1054,7 +1054,7 @@ pub struct InherentTyOutside {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_coerce_unsized_may, code = "E0378")]
+#[diag(hir_analysis_coerce_unsized_may, code = E0378)]
 pub struct DispatchFromDynCoercion<'a> {
     #[primary_span]
     pub span: Span,
@@ -1066,14 +1066,14 @@ pub struct DispatchFromDynCoercion<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_dispatch_from_dyn_repr, code = "E0378")]
+#[diag(hir_analysis_dispatch_from_dyn_repr, code = E0378)]
 pub struct DispatchFromDynRepr {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_inherent_ty_outside_relevant, code = "E0390")]
+#[diag(hir_analysis_inherent_ty_outside_relevant, code = E0390)]
 #[help]
 pub struct InherentTyOutsideRelevant {
     #[primary_span]
@@ -1083,7 +1083,7 @@ pub struct InherentTyOutsideRelevant {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_inherent_ty_outside_new, code = "E0116")]
+#[diag(hir_analysis_inherent_ty_outside_new, code = E0116)]
 #[note]
 pub struct InherentTyOutsideNew {
     #[primary_span]
@@ -1092,7 +1092,7 @@ pub struct InherentTyOutsideNew {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_inherent_ty_outside_primitive, code = "E0390")]
+#[diag(hir_analysis_inherent_ty_outside_primitive, code = E0390)]
 #[help]
 pub struct InherentTyOutsidePrimitive {
     #[primary_span]
@@ -1102,7 +1102,7 @@ pub struct InherentTyOutsidePrimitive {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_inherent_primitive_ty, code = "E0390")]
+#[diag(hir_analysis_inherent_primitive_ty, code = E0390)]
 #[help]
 pub struct InherentPrimitiveTy<'a> {
     #[primary_span]
@@ -1118,7 +1118,7 @@ pub struct InherentPrimitiveTyNote<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_inherent_dyn, code = "E0785")]
+#[diag(hir_analysis_inherent_dyn, code = E0785)]
 #[note]
 pub struct InherentDyn {
     #[primary_span]
@@ -1127,7 +1127,7 @@ pub struct InherentDyn {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_inherent_nominal, code = "E0118")]
+#[diag(hir_analysis_inherent_nominal, code = E0118)]
 #[note]
 pub struct InherentNominal {
     #[primary_span]
@@ -1136,7 +1136,7 @@ pub struct InherentNominal {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_dispatch_from_dyn_zst, code = "E0378")]
+#[diag(hir_analysis_dispatch_from_dyn_zst, code = E0378)]
 #[note]
 pub struct DispatchFromDynZST<'a> {
     #[primary_span]
@@ -1146,7 +1146,7 @@ pub struct DispatchFromDynZST<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_coerce_unsized_may, code = "E0378")]
+#[diag(hir_analysis_coerce_unsized_may, code = E0378)]
 pub struct DispatchFromDynSingle<'a> {
     #[primary_span]
     pub span: Span,
@@ -1156,7 +1156,7 @@ pub struct DispatchFromDynSingle<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_dispatch_from_dyn_multi, code = "E0378")]
+#[diag(hir_analysis_dispatch_from_dyn_multi, code = E0378)]
 #[note]
 pub struct DispatchFromDynMulti {
     #[primary_span]
@@ -1168,7 +1168,7 @@ pub struct DispatchFromDynMulti {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_coerce_unsized_may, code = "E0376")]
+#[diag(hir_analysis_coerce_unsized_may, code = E0376)]
 pub struct DispatchFromDynStruct<'a> {
     #[primary_span]
     pub span: Span,
@@ -1176,7 +1176,7 @@ pub struct DispatchFromDynStruct<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_coerce_unsized_may, code = "E0377")]
+#[diag(hir_analysis_coerce_unsized_may, code = E0377)]
 pub struct DispatchFromDynSame<'a> {
     #[primary_span]
     pub span: Span,
@@ -1188,7 +1188,7 @@ pub struct DispatchFromDynSame<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_coerce_unsized_may, code = "E0374")]
+#[diag(hir_analysis_coerce_unsized_may, code = E0374)]
 pub struct CoerceUnsizedOneField<'a> {
     #[primary_span]
     pub span: Span,
@@ -1198,7 +1198,7 @@ pub struct CoerceUnsizedOneField<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_coerce_unsized_multi, code = "E0375")]
+#[diag(hir_analysis_coerce_unsized_multi, code = E0375)]
 #[note]
 pub struct CoerceUnsizedMulti {
     #[primary_span]
@@ -1211,7 +1211,7 @@ pub struct CoerceUnsizedMulti {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_coerce_unsized_may, code = "E0378")]
+#[diag(hir_analysis_coerce_unsized_may, code = E0378)]
 pub struct CoerceUnsizedMay<'a> {
     #[primary_span]
     pub span: Span,
@@ -1219,7 +1219,7 @@ pub struct CoerceUnsizedMay<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_trait_cannot_impl_for_ty, code = "E0204")]
+#[diag(hir_analysis_trait_cannot_impl_for_ty, code = E0204)]
 pub struct TraitCannotImplForTy {
     #[primary_span]
     pub span: Span,
@@ -1241,7 +1241,7 @@ pub struct ImplForTyRequires {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_traits_with_defualt_impl, code = "E0321")]
+#[diag(hir_analysis_traits_with_defualt_impl, code = E0321)]
 #[note]
 pub struct TraitsWithDefaultImpl<'a> {
     #[primary_span]
@@ -1252,7 +1252,7 @@ pub struct TraitsWithDefaultImpl<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_cross_crate_traits, code = "E0321")]
+#[diag(hir_analysis_cross_crate_traits, code = E0321)]
 pub struct CrossCrateTraits<'a> {
     #[primary_span]
     #[label]
@@ -1262,7 +1262,7 @@ pub struct CrossCrateTraits<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_cross_crate_traits_defined, code = "E0321")]
+#[diag(hir_analysis_cross_crate_traits_defined, code = E0321)]
 pub struct CrossCrateTraitsDefined {
     #[primary_span]
     #[label]
@@ -1271,7 +1271,7 @@ pub struct CrossCrateTraitsDefined {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_ty_param_first_local, code = "E0210")]
+#[diag(hir_analysis_ty_param_first_local, code = E0210)]
 #[note]
 pub struct TyParamFirstLocal<'a> {
     #[primary_span]
@@ -1284,7 +1284,7 @@ pub struct TyParamFirstLocal<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_ty_param_some, code = "E0210")]
+#[diag(hir_analysis_ty_param_some, code = E0210)]
 #[note]
 pub struct TyParamSome<'a> {
     #[primary_span]
@@ -1297,7 +1297,7 @@ pub struct TyParamSome<'a> {
 
 #[derive(Diagnostic)]
 pub enum OnlyCurrentTraits<'a> {
-    #[diag(hir_analysis_only_current_traits_outside, code = "E0117")]
+    #[diag(hir_analysis_only_current_traits_outside, code = E0117)]
     Outside {
         #[primary_span]
         #[label(hir_analysis_only_current_traits_label)]
@@ -1317,7 +1317,7 @@ pub enum OnlyCurrentTraits<'a> {
         #[subdiagnostic]
         sugg: Option<OnlyCurrentTraitsPointerSugg<'a>>,
     },
-    #[diag(hir_analysis_only_current_traits_primitive, code = "E0117")]
+    #[diag(hir_analysis_only_current_traits_primitive, code = E0117)]
     Primitive {
         #[primary_span]
         #[label(hir_analysis_only_current_traits_label)]
@@ -1337,7 +1337,7 @@ pub enum OnlyCurrentTraits<'a> {
         #[subdiagnostic]
         sugg: Option<OnlyCurrentTraitsPointerSugg<'a>>,
     },
-    #[diag(hir_analysis_only_current_traits_arbitrary, code = "E0117")]
+    #[diag(hir_analysis_only_current_traits_arbitrary, code = E0117)]
     Arbitrary {
         #[primary_span]
         #[label(hir_analysis_only_current_traits_label)]
@@ -1412,7 +1412,7 @@ pub struct OnlyCurrentTraitsPointerSugg<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_static_mut_ref, code = "E0796")]
+#[diag(hir_analysis_static_mut_ref, code = E0796)]
 #[note]
 pub struct StaticMutRef {
     #[primary_span]
diff --git a/compiler/rustc_hir_analysis/src/impl_wf_check.rs b/compiler/rustc_hir_analysis/src/impl_wf_check.rs
index 2fe08ead72b..c072891e295 100644
--- a/compiler/rustc_hir_analysis/src/impl_wf_check.rs
+++ b/compiler/rustc_hir_analysis/src/impl_wf_check.rs
@@ -12,7 +12,7 @@
 use min_specialization::check_min_specialization;
 
 use rustc_data_structures::fx::FxHashSet;
-use rustc_errors::struct_span_code_err;
+use rustc_errors::{codes::*, struct_span_code_err};
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{LocalDefId, LocalModDefId};
 use rustc_middle::query::Providers;
diff --git a/compiler/rustc_hir_analysis/src/structured_errors.rs b/compiler/rustc_hir_analysis/src/structured_errors.rs
index b061d637138..6846e4defe5 100644
--- a/compiler/rustc_hir_analysis/src/structured_errors.rs
+++ b/compiler/rustc_hir_analysis/src/structured_errors.rs
@@ -6,18 +6,18 @@
     missing_cast_for_variadic_arg::*, sized_unsized_cast::*, wrong_number_of_generic_args::*,
 };
 
-use rustc_errors::DiagnosticBuilder;
+use rustc_errors::{DiagnosticBuilder, ErrCode};
 use rustc_session::Session;
 
 pub trait StructuredDiagnostic<'tcx> {
     fn session(&self) -> &Session;
 
-    fn code(&self) -> String;
+    fn code(&self) -> ErrCode;
 
     fn diagnostic(&self) -> DiagnosticBuilder<'tcx> {
         let err = self.diagnostic_common();
 
-        if self.session().teach(&self.code()) {
+        if self.session().teach(self.code()) {
             self.diagnostic_extended(err)
         } else {
             self.diagnostic_regular(err)
diff --git a/compiler/rustc_hir_analysis/src/structured_errors/missing_cast_for_variadic_arg.rs b/compiler/rustc_hir_analysis/src/structured_errors/missing_cast_for_variadic_arg.rs
index 6f4435db411..50b4ef623ac 100644
--- a/compiler/rustc_hir_analysis/src/structured_errors/missing_cast_for_variadic_arg.rs
+++ b/compiler/rustc_hir_analysis/src/structured_errors/missing_cast_for_variadic_arg.rs
@@ -1,5 +1,5 @@
 use crate::{errors, structured_errors::StructuredDiagnostic};
-use rustc_errors::DiagnosticBuilder;
+use rustc_errors::{codes::*, DiagnosticBuilder, ErrCode};
 use rustc_middle::ty::{Ty, TypeVisitableExt};
 use rustc_session::Session;
 use rustc_span::Span;
@@ -16,8 +16,8 @@ fn session(&self) -> &Session {
         self.sess
     }
 
-    fn code(&self) -> String {
-        rustc_errors::error_code!(E0617)
+    fn code(&self) -> ErrCode {
+        E0617
     }
 
     fn diagnostic_common(&self) -> DiagnosticBuilder<'tcx> {
diff --git a/compiler/rustc_hir_analysis/src/structured_errors/sized_unsized_cast.rs b/compiler/rustc_hir_analysis/src/structured_errors/sized_unsized_cast.rs
index 19cac4a38aa..54d54a2af93 100644
--- a/compiler/rustc_hir_analysis/src/structured_errors/sized_unsized_cast.rs
+++ b/compiler/rustc_hir_analysis/src/structured_errors/sized_unsized_cast.rs
@@ -1,5 +1,5 @@
 use crate::{errors, structured_errors::StructuredDiagnostic};
-use rustc_errors::DiagnosticBuilder;
+use rustc_errors::{codes::*, DiagnosticBuilder, ErrCode};
 use rustc_middle::ty::{Ty, TypeVisitableExt};
 use rustc_session::Session;
 use rustc_span::Span;
@@ -16,8 +16,8 @@ fn session(&self) -> &Session {
         self.sess
     }
 
-    fn code(&self) -> String {
-        rustc_errors::error_code!(E0607)
+    fn code(&self) -> ErrCode {
+        E0607
     }
 
     fn diagnostic_common(&self) -> DiagnosticBuilder<'tcx> {
diff --git a/compiler/rustc_hir_analysis/src/structured_errors/wrong_number_of_generic_args.rs b/compiler/rustc_hir_analysis/src/structured_errors/wrong_number_of_generic_args.rs
index ba81e7f1f81..501915d2e7e 100644
--- a/compiler/rustc_hir_analysis/src/structured_errors/wrong_number_of_generic_args.rs
+++ b/compiler/rustc_hir_analysis/src/structured_errors/wrong_number_of_generic_args.rs
@@ -1,5 +1,7 @@
 use crate::structured_errors::StructuredDiagnostic;
-use rustc_errors::{pluralize, Applicability, Diagnostic, DiagnosticBuilder, MultiSpan};
+use rustc_errors::{
+    codes::*, pluralize, Applicability, Diagnostic, DiagnosticBuilder, ErrCode, MultiSpan,
+};
 use rustc_hir as hir;
 use rustc_middle::ty::{self as ty, AssocItems, AssocKind, TyCtxt};
 use rustc_session::Session;
@@ -1105,8 +1107,8 @@ fn session(&self) -> &Session {
         self.tcx.sess
     }
 
-    fn code(&self) -> String {
-        rustc_errors::error_code!(E0107)
+    fn code(&self) -> ErrCode {
+        E0107
     }
 
     fn diagnostic_common(&self) -> DiagnosticBuilder<'tcx> {
diff --git a/compiler/rustc_hir_typeck/src/cast.rs b/compiler/rustc_hir_typeck/src/cast.rs
index bd8a2024caa..a0ac839f3dd 100644
--- a/compiler/rustc_hir_typeck/src/cast.rs
+++ b/compiler/rustc_hir_typeck/src/cast.rs
@@ -33,7 +33,7 @@
 use crate::errors;
 use crate::type_error_struct;
 use hir::ExprKind;
-use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
+use rustc_errors::{codes::*, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
 use rustc_hir as hir;
 use rustc_macros::{TypeFoldable, TypeVisitable};
 use rustc_middle::mir::Mutability;
diff --git a/compiler/rustc_hir_typeck/src/coercion.rs b/compiler/rustc_hir_typeck/src/coercion.rs
index 858faf161f6..ca636ebcade 100644
--- a/compiler/rustc_hir_typeck/src/coercion.rs
+++ b/compiler/rustc_hir_typeck/src/coercion.rs
@@ -36,7 +36,9 @@
 //! ```
 
 use crate::FnCtxt;
-use rustc_errors::{struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder, MultiSpan};
+use rustc_errors::{
+    codes::*, struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder, MultiSpan,
+};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::{self, Visitor};
diff --git a/compiler/rustc_hir_typeck/src/errors.rs b/compiler/rustc_hir_typeck/src/errors.rs
index 4f929068887..b75cf4b4e8b 100644
--- a/compiler/rustc_hir_typeck/src/errors.rs
+++ b/compiler/rustc_hir_typeck/src/errors.rs
@@ -3,8 +3,8 @@
 
 use crate::fluent_generated as fluent;
 use rustc_errors::{
-    AddToDiagnostic, Applicability, Diagnostic, DiagnosticArgValue, IntoDiagnosticArg, MultiSpan,
-    SubdiagnosticMessage,
+    codes::*, AddToDiagnostic, Applicability, Diagnostic, DiagnosticArgValue, IntoDiagnosticArg,
+    MultiSpan, SubdiagnosticMessage,
 };
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
 use rustc_middle::ty::Ty;
@@ -15,7 +15,7 @@
 };
 
 #[derive(Diagnostic)]
-#[diag(hir_typeck_field_multiply_specified_in_initializer, code = "E0062")]
+#[diag(hir_typeck_field_multiply_specified_in_initializer, code = E0062)]
 pub struct FieldMultiplySpecifiedInInitializer {
     #[primary_span]
     #[label]
@@ -26,7 +26,7 @@ pub struct FieldMultiplySpecifiedInInitializer {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_typeck_return_stmt_outside_of_fn_body, code = "E0572")]
+#[diag(hir_typeck_return_stmt_outside_of_fn_body, code = E0572)]
 pub struct ReturnStmtOutsideOfFnBody {
     #[primary_span]
     pub span: Span,
@@ -62,14 +62,14 @@ pub struct RustCallIncorrectArgs {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_typeck_yield_expr_outside_of_coroutine, code = "E0627")]
+#[diag(hir_typeck_yield_expr_outside_of_coroutine, code = E0627)]
 pub struct YieldExprOutsideOfCoroutine {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_typeck_struct_expr_non_exhaustive, code = "E0639")]
+#[diag(hir_typeck_struct_expr_non_exhaustive, code = E0639)]
 pub struct StructExprNonExhaustive {
     #[primary_span]
     pub span: Span,
@@ -77,7 +77,7 @@ pub struct StructExprNonExhaustive {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_typeck_method_call_on_unknown_raw_pointee, code = "E0699")]
+#[diag(hir_typeck_method_call_on_unknown_raw_pointee, code = E0699)]
 pub struct MethodCallOnUnknownRawPointee {
     #[primary_span]
     pub span: Span,
@@ -92,14 +92,14 @@ pub struct MissingFnLangItems {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_typeck_functional_record_update_on_non_struct, code = "E0436")]
+#[diag(hir_typeck_functional_record_update_on_non_struct, code = E0436)]
 pub struct FunctionalRecordUpdateOnNonStruct {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_typeck_address_of_temporary_taken, code = "E0745")]
+#[diag(hir_typeck_address_of_temporary_taken, code = E0745)]
 pub struct AddressOfTemporaryTaken {
     #[primary_span]
     #[label]
@@ -145,7 +145,7 @@ pub enum ExpectedReturnTypeLabel<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_typeck_explicit_destructor, code = "E0040")]
+#[diag(hir_typeck_explicit_destructor, code = E0040)]
 pub struct ExplicitDestructorCall {
     #[primary_span]
     #[label]
@@ -168,7 +168,7 @@ pub enum ExplicitDestructorCallSugg {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_typeck_missing_parentheses_in_range, code = "E0689")]
+#[diag(hir_typeck_missing_parentheses_in_range, code = E0689)]
 pub struct MissingParenthesesInRange {
     #[primary_span]
     #[label(hir_typeck_missing_parentheses_in_range)]
@@ -321,7 +321,7 @@ pub fn new() -> Self {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_typeck_invalid_callee, code = "E0618")]
+#[diag(hir_typeck_invalid_callee, code = E0618)]
 pub struct InvalidCallee {
     #[primary_span]
     pub span: Span,
@@ -329,7 +329,7 @@ pub struct InvalidCallee {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_typeck_int_to_fat, code = "E0606")]
+#[diag(hir_typeck_int_to_fat, code = E0606)]
 pub struct IntToWide<'tcx> {
     #[primary_span]
     #[label(hir_typeck_int_to_fat_label)]
@@ -510,7 +510,7 @@ pub struct TrivialCast<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_typeck_no_associated_item, code = "E0599")]
+#[diag(hir_typeck_no_associated_item, code = E0599)]
 pub struct NoAssociatedItem {
     #[primary_span]
     pub span: Span,
@@ -532,7 +532,7 @@ pub struct CandidateTraitNote {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_typeck_cannot_cast_to_bool, code = "E0054")]
+#[diag(hir_typeck_cannot_cast_to_bool, code = E0054)]
 pub struct CannotCastToBool<'tcx> {
     #[primary_span]
     pub span: Span,
@@ -549,7 +549,7 @@ pub struct CastEnumDrop<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_typeck_cast_unknown_pointer, code = "E0641")]
+#[diag(hir_typeck_cast_unknown_pointer, code = E0641)]
 pub struct CastUnknownPointer {
     #[primary_span]
     pub span: Span,
@@ -600,7 +600,7 @@ pub enum CannotCastToBoolHelp {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_typeck_ctor_is_private, code = "E0603")]
+#[diag(hir_typeck_ctor_is_private, code = E0603)]
 pub struct CtorIsPrivate {
     #[primary_span]
     pub span: Span,
diff --git a/compiler/rustc_hir_typeck/src/expr.rs b/compiler/rustc_hir_typeck/src/expr.rs
index 3bc259c17b7..fafed5be8c5 100644
--- a/compiler/rustc_hir_typeck/src/expr.rs
+++ b/compiler/rustc_hir_typeck/src/expr.rs
@@ -25,8 +25,8 @@
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_errors::{
-    pluralize, struct_span_code_err, AddToDiagnostic, Applicability, Diagnostic, DiagnosticBuilder,
-    ErrorGuaranteed, StashKey,
+    codes::*, pluralize, struct_span_code_err, AddToDiagnostic, Applicability, Diagnostic,
+    DiagnosticBuilder, ErrCode, ErrorGuaranteed, StashKey,
 };
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, DefKind, Res};
@@ -527,7 +527,7 @@ pub(crate) fn check_expr_path(
                 Ty::new_error(tcx, e)
             }
             Res::Def(DefKind::Variant, _) => {
-                let e = report_unexpected_variant_res(tcx, res, qpath, expr.span, "E0533", "value");
+                let e = report_unexpected_variant_res(tcx, res, qpath, expr.span, E0533, "value");
                 Ty::new_error(tcx, e)
             }
             _ => self.instantiate_value_path(segs, opt_ty, res, expr.span, expr.hir_id).0,
@@ -939,7 +939,7 @@ fn point_at_return_for_opaque_ty_error(
     pub(crate) fn check_lhs_assignable(
         &self,
         lhs: &'tcx hir::Expr<'tcx>,
-        err_code: &'static str,
+        code: ErrCode,
         op_span: Span,
         adjust_err: impl FnOnce(&mut Diagnostic),
     ) {
@@ -948,7 +948,7 @@ pub(crate) fn check_lhs_assignable(
         }
 
         let mut err = self.dcx().struct_span_err(op_span, "invalid left-hand side of assignment");
-        err.code(err_code.into());
+        err.code(code);
         err.span_label(lhs.span, "cannot assign to this expression");
 
         self.comes_from_while_condition(lhs.hir_id, |expr| {
@@ -1244,7 +1244,7 @@ fn check_expr_assign(
             diag.emit();
         }
 
-        self.check_lhs_assignable(lhs, "E0070", span, |err| {
+        self.check_lhs_assignable(lhs, E0070, span, |err| {
             if let Some(rhs_ty) = self.typeck_results.borrow().expr_ty_opt(rhs) {
                 suggest_deref_binop(err, rhs_ty);
             }
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
index 6a77450f075..2494feee1ff 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
@@ -12,7 +12,9 @@
 use itertools::Itertools;
 use rustc_ast as ast;
 use rustc_data_structures::fx::FxIndexSet;
-use rustc_errors::{pluralize, Applicability, Diagnostic, ErrorGuaranteed, MultiSpan, StashKey};
+use rustc_errors::{
+    codes::*, pluralize, Applicability, Diagnostic, ErrCode, ErrorGuaranteed, MultiSpan, StashKey,
+};
 use rustc_hir as hir;
 use rustc_hir::def::{CtorOf, DefKind, Res};
 use rustc_hir::def_id::DefId;
@@ -177,7 +179,7 @@ pub(in super::super) fn check_argument_types(
             self.register_wf_obligation(fn_input_ty.into(), arg_expr.span, traits::MiscObligation);
         }
 
-        let mut err_code = "E0061";
+        let mut err_code = E0061;
 
         // If the arguments should be wrapped in a tuple (ex: closures), unwrap them here
         let (formal_input_tys, expected_input_tys) = if tuple_arguments == TupleArguments {
@@ -187,7 +189,7 @@ pub(in super::super) fn check_argument_types(
                 ty::Tuple(arg_types) => {
                     // Argument length differs
                     if arg_types.len() != provided_args.len() {
-                        err_code = "E0057";
+                        err_code = E0057;
                     }
                     let expected_input_tys = match expected_input_tys {
                         Some(expected_input_tys) => match expected_input_tys.get(0) {
@@ -358,7 +360,7 @@ pub(in super::super) fn check_argument_types(
         }
 
         if c_variadic && provided_arg_count < minimum_input_count {
-            err_code = "E0060";
+            err_code = E0060;
         }
 
         for arg in provided_args.iter().skip(minimum_input_count) {
@@ -443,7 +445,7 @@ fn report_arg_errors(
         formal_and_expected_inputs: IndexVec<ExpectedIdx, (Ty<'tcx>, Ty<'tcx>)>,
         provided_args: IndexVec<ProvidedIdx, &'tcx hir::Expr<'tcx>>,
         c_variadic: bool,
-        err_code: &str,
+        err_code: ErrCode,
         fn_def_id: Option<DefId>,
         call_span: Span,
         call_expr: &'tcx hir::Expr<'tcx>,
diff --git a/compiler/rustc_hir_typeck/src/intrinsicck.rs b/compiler/rustc_hir_typeck/src/intrinsicck.rs
index e087733130e..2dee5093e87 100644
--- a/compiler/rustc_hir_typeck/src/intrinsicck.rs
+++ b/compiler/rustc_hir_typeck/src/intrinsicck.rs
@@ -1,5 +1,5 @@
 use hir::HirId;
-use rustc_errors::struct_span_code_err;
+use rustc_errors::{codes::*, struct_span_code_err};
 use rustc_hir as hir;
 use rustc_index::Idx;
 use rustc_middle::ty::layout::{LayoutError, SizeSkeleton};
diff --git a/compiler/rustc_hir_typeck/src/lib.rs b/compiler/rustc_hir_typeck/src/lib.rs
index 36cd6583147..36aa949668f 100644
--- a/compiler/rustc_hir_typeck/src/lib.rs
+++ b/compiler/rustc_hir_typeck/src/lib.rs
@@ -51,7 +51,7 @@
 use crate::fn_ctxt::LoweredTy;
 use crate::gather_locals::GatherLocalsVisitor;
 use rustc_data_structures::unord::UnordSet;
-use rustc_errors::{struct_span_code_err, ErrorGuaranteed};
+use rustc_errors::{codes::*, struct_span_code_err, ErrCode, ErrorGuaranteed};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::intravisit::Visitor;
@@ -71,7 +71,7 @@
 
 #[macro_export]
 macro_rules! type_error_struct {
-    ($dcx:expr, $span:expr, $typ:expr, $code:ident, $($message:tt)*) => ({
+    ($dcx:expr, $span:expr, $typ:expr, $code:expr, $($message:tt)*) => ({
         let mut err = rustc_errors::struct_span_code_err!($dcx, $span, $code, $($message)*);
 
         if $typ.references_error() {
@@ -375,7 +375,7 @@ fn report_unexpected_variant_res(
     res: Res,
     qpath: &hir::QPath<'_>,
     span: Span,
-    err_code: &str,
+    err_code: ErrCode,
     expected: &str,
 ) -> ErrorGuaranteed {
     let res_descr = match res {
@@ -386,9 +386,9 @@ fn report_unexpected_variant_res(
     let err = tcx
         .dcx()
         .struct_span_err(span, format!("expected {expected}, found {res_descr} `{path_str}`"))
-        .with_code(err_code.into());
+        .with_code(err_code);
     match res {
-        Res::Def(DefKind::Fn | DefKind::AssocFn, _) if err_code == "E0164" => {
+        Res::Def(DefKind::Fn | DefKind::AssocFn, _) if err_code == E0164 => {
             let patterns_url = "https://doc.rust-lang.org/book/ch18-00-patterns.html";
             err.with_span_label(span, "`fn` calls are not allowed in patterns")
                 .with_help(format!("for more information, visit {patterns_url}"))
diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs
index 47f6e3f934e..314d28e6e04 100644
--- a/compiler/rustc_hir_typeck/src/method/suggest.rs
+++ b/compiler/rustc_hir_typeck/src/method/suggest.rs
@@ -3,17 +3,16 @@
 
 // ignore-tidy-filelength
 
-use crate::errors;
-use crate::errors::{CandidateTraitNote, NoAssociatedItem};
+use crate::errors::{self, CandidateTraitNote, NoAssociatedItem};
 use crate::Expectation;
 use crate::FnCtxt;
 use rustc_ast::ast::Mutability;
 use rustc_attr::parse_confusables;
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_data_structures::unord::UnordSet;
-use rustc_errors::StashKey;
 use rustc_errors::{
-    pluralize, struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder, MultiSpan,
+    codes::*, pluralize, struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder,
+    MultiSpan, StashKey,
 };
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
diff --git a/compiler/rustc_hir_typeck/src/op.rs b/compiler/rustc_hir_typeck/src/op.rs
index ff82e2d653c..bbe6d9e9670 100644
--- a/compiler/rustc_hir_typeck/src/op.rs
+++ b/compiler/rustc_hir_typeck/src/op.rs
@@ -5,7 +5,7 @@
 use crate::Expectation;
 use rustc_ast as ast;
 use rustc_data_structures::packed::Pu128;
-use rustc_errors::{struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder};
+use rustc_errors::{codes::*, struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder};
 use rustc_hir as hir;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_infer::traits::ObligationCauseCode;
@@ -44,7 +44,7 @@ pub fn check_binop_assign(
                 return_ty
             };
 
-        self.check_lhs_assignable(lhs, "E0067", op.span, |err| {
+        self.check_lhs_assignable(lhs, E0067, op.span, |err| {
             if let Some(lhs_deref_ty) = self.deref_once_mutably_for_diagnostic(lhs_ty) {
                 if self
                     .lookup_op_method(
diff --git a/compiler/rustc_hir_typeck/src/pat.rs b/compiler/rustc_hir_typeck/src/pat.rs
index e31eeab4c4a..a611d0eda85 100644
--- a/compiler/rustc_hir_typeck/src/pat.rs
+++ b/compiler/rustc_hir_typeck/src/pat.rs
@@ -3,8 +3,8 @@
 use rustc_ast as ast;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::{
-    pluralize, struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
-    MultiSpan,
+    codes::*, pluralize, struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder,
+    ErrorGuaranteed, MultiSpan,
 };
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, DefKind, Res};
@@ -576,7 +576,7 @@ fn emit_err_pat_range(
         if (lhs, rhs).references_error() {
             err.downgrade_to_delayed_bug();
         }
-        if self.tcx.sess.teach(&err.get_code().unwrap()) {
+        if self.tcx.sess.teach(err.get_code().unwrap()) {
             err.note(
                 "In a match expression, only numbers and characters can be matched \
                     against a range. This is because the compiler checks that the range \
@@ -847,7 +847,7 @@ pub fn check_dereferenceable(
                 type_str
             );
             err.span_label(span, format!("type `{type_str}` cannot be dereferenced"));
-            if self.tcx.sess.teach(&err.get_code().unwrap()) {
+            if self.tcx.sess.teach(err.get_code().unwrap()) {
                 err.note(CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ);
             }
             return Err(err.emit());
@@ -907,7 +907,7 @@ fn check_pat_path(
             }
             Res::Def(DefKind::AssocFn | DefKind::Ctor(_, CtorKind::Fn) | DefKind::Variant, _) => {
                 let expected = "unit struct, unit variant or constant";
-                let e = report_unexpected_variant_res(tcx, res, qpath, pat.span, "E0533", expected);
+                let e = report_unexpected_variant_res(tcx, res, qpath, pat.span, E0533, expected);
                 return Ty::new_error(tcx, e);
             }
             Res::SelfCtor(..)
@@ -1061,7 +1061,7 @@ fn check_pat_tuple_struct(
         };
         let report_unexpected_res = |res: Res| {
             let expected = "tuple struct or tuple variant";
-            let e = report_unexpected_variant_res(tcx, res, qpath, pat.span, "E0164", expected);
+            let e = report_unexpected_variant_res(tcx, res, qpath, pat.span, E0164, expected);
             on_error(e);
             e
         };
@@ -1669,7 +1669,7 @@ fn error_inexistent_fields(
                 }
             }
         }
-        if tcx.sess.teach(&err.get_code().unwrap()) {
+        if tcx.sess.teach(err.get_code().unwrap()) {
             err.note(
                 "This error indicates that a struct pattern attempted to \
                  extract a nonexistent field from a struct. Struct fields \
diff --git a/compiler/rustc_infer/src/errors/mod.rs b/compiler/rustc_infer/src/errors/mod.rs
index aee99063e03..4e9f573091b 100644
--- a/compiler/rustc_infer/src/errors/mod.rs
+++ b/compiler/rustc_infer/src/errors/mod.rs
@@ -1,7 +1,7 @@
 use hir::GenericParamKind;
 use rustc_errors::{
-    AddToDiagnostic, Applicability, Diagnostic, DiagnosticMessage, DiagnosticStyledString,
-    IntoDiagnosticArg, MultiSpan, SubdiagnosticMessage,
+    codes::*, AddToDiagnostic, Applicability, Diagnostic, DiagnosticMessage,
+    DiagnosticStyledString, IntoDiagnosticArg, MultiSpan, SubdiagnosticMessage,
 };
 use rustc_hir as hir;
 use rustc_hir::FnRetTy;
@@ -33,7 +33,7 @@ pub struct OpaqueHiddenTypeDiag {
 }
 
 #[derive(Diagnostic)]
-#[diag(infer_type_annotations_needed, code = "E0282")]
+#[diag(infer_type_annotations_needed, code = E0282)]
 pub struct AnnotationRequired<'a> {
     #[primary_span]
     pub span: Span,
@@ -51,7 +51,7 @@ pub struct AnnotationRequired<'a> {
 
 // Copy of `AnnotationRequired` for E0283
 #[derive(Diagnostic)]
-#[diag(infer_type_annotations_needed, code = "E0283")]
+#[diag(infer_type_annotations_needed, code = E0283)]
 pub struct AmbiguousImpl<'a> {
     #[primary_span]
     pub span: Span,
@@ -69,7 +69,7 @@ pub struct AmbiguousImpl<'a> {
 
 // Copy of `AnnotationRequired` for E0284
 #[derive(Diagnostic)]
-#[diag(infer_type_annotations_needed, code = "E0284")]
+#[diag(infer_type_annotations_needed, code = E0284)]
 pub struct AmbiguousReturn<'a> {
     #[primary_span]
     pub span: Span,
@@ -421,7 +421,7 @@ fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
 }
 
 #[derive(Diagnostic)]
-#[diag(infer_lifetime_mismatch, code = "E0623")]
+#[diag(infer_lifetime_mismatch, code = E0623)]
 pub struct LifetimeMismatch<'a> {
     #[primary_span]
     pub span: Span,
@@ -495,7 +495,7 @@ pub struct MismatchedStaticLifetime<'a> {
 
 #[derive(Diagnostic)]
 pub enum ExplicitLifetimeRequired<'a> {
-    #[diag(infer_explicit_lifetime_required_with_ident, code = "E0621")]
+    #[diag(infer_explicit_lifetime_required_with_ident, code = E0621)]
     WithIdent {
         #[primary_span]
         #[label]
@@ -511,7 +511,7 @@ pub enum ExplicitLifetimeRequired<'a> {
         #[skip_arg]
         new_ty: Ty<'a>,
     },
-    #[diag(infer_explicit_lifetime_required_with_param_type, code = "E0621")]
+    #[diag(infer_explicit_lifetime_required_with_param_type, code = E0621)]
     WithParamType {
         #[primary_span]
         #[label]
@@ -819,7 +819,7 @@ fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, f: F)
 }
 
 #[derive(Diagnostic)]
-#[diag(infer_but_calling_introduces, code = "E0772")]
+#[diag(infer_but_calling_introduces, code = E0772)]
 pub struct ButCallingIntroduces {
     #[label(infer_label1)]
     pub param_ty_span: Span,
@@ -871,14 +871,14 @@ fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _f: F)
     where
         F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
     {
-        diag.code(rustc_errors::error_code!(E0772));
+        diag.code(E0772);
         diag.primary_message(fluent::infer_more_targeted);
         diag.arg("ident", self.ident);
     }
 }
 
 #[derive(Diagnostic)]
-#[diag(infer_but_needs_to_satisfy, code = "E0759")]
+#[diag(infer_but_needs_to_satisfy, code = E0759)]
 pub struct ButNeedsToSatisfy {
     #[primary_span]
     pub sp: Span,
@@ -904,7 +904,7 @@ pub struct ButNeedsToSatisfy {
 }
 
 #[derive(Diagnostic)]
-#[diag(infer_outlives_content, code = "E0312")]
+#[diag(infer_outlives_content, code = E0312)]
 pub struct OutlivesContent<'a> {
     #[primary_span]
     pub span: Span,
@@ -913,7 +913,7 @@ pub struct OutlivesContent<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(infer_outlives_bound, code = "E0476")]
+#[diag(infer_outlives_bound, code = E0476)]
 pub struct OutlivesBound<'a> {
     #[primary_span]
     pub span: Span,
@@ -922,7 +922,7 @@ pub struct OutlivesBound<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(infer_fulfill_req_lifetime, code = "E0477")]
+#[diag(infer_fulfill_req_lifetime, code = E0477)]
 pub struct FulfillReqLifetime<'a> {
     #[primary_span]
     pub span: Span,
@@ -932,7 +932,7 @@ pub struct FulfillReqLifetime<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(infer_lf_bound_not_satisfied, code = "E0478")]
+#[diag(infer_lf_bound_not_satisfied, code = E0478)]
 pub struct LfBoundNotSatisfied<'a> {
     #[primary_span]
     pub span: Span,
@@ -941,7 +941,7 @@ pub struct LfBoundNotSatisfied<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(infer_ref_longer_than_data, code = "E0491")]
+#[diag(infer_ref_longer_than_data, code = E0491)]
 pub struct RefLongerThanData<'a> {
     #[primary_span]
     pub span: Span,
@@ -1117,7 +1117,7 @@ pub enum PlaceholderRelationLfNotSatisfied {
 }
 
 #[derive(Diagnostic)]
-#[diag(infer_opaque_captures_lifetime, code = "E0700")]
+#[diag(infer_opaque_captures_lifetime, code = E0700)]
 pub struct OpaqueCapturesLifetime<'tcx> {
     #[primary_span]
     pub span: Span,
@@ -1378,73 +1378,73 @@ pub enum TypeErrorAdditionalDiags {
 
 #[derive(Diagnostic)]
 pub enum ObligationCauseFailureCode {
-    #[diag(infer_oc_method_compat, code = "E0308")]
+    #[diag(infer_oc_method_compat, code = E0308)]
     MethodCompat {
         #[primary_span]
         span: Span,
         #[subdiagnostic]
         subdiags: Vec<TypeErrorAdditionalDiags>,
     },
-    #[diag(infer_oc_type_compat, code = "E0308")]
+    #[diag(infer_oc_type_compat, code = E0308)]
     TypeCompat {
         #[primary_span]
         span: Span,
         #[subdiagnostic]
         subdiags: Vec<TypeErrorAdditionalDiags>,
     },
-    #[diag(infer_oc_const_compat, code = "E0308")]
+    #[diag(infer_oc_const_compat, code = E0308)]
     ConstCompat {
         #[primary_span]
         span: Span,
         #[subdiagnostic]
         subdiags: Vec<TypeErrorAdditionalDiags>,
     },
-    #[diag(infer_oc_try_compat, code = "E0308")]
+    #[diag(infer_oc_try_compat, code = E0308)]
     TryCompat {
         #[primary_span]
         span: Span,
         #[subdiagnostic]
         subdiags: Vec<TypeErrorAdditionalDiags>,
     },
-    #[diag(infer_oc_match_compat, code = "E0308")]
+    #[diag(infer_oc_match_compat, code = E0308)]
     MatchCompat {
         #[primary_span]
         span: Span,
         #[subdiagnostic]
         subdiags: Vec<TypeErrorAdditionalDiags>,
     },
-    #[diag(infer_oc_if_else_different, code = "E0308")]
+    #[diag(infer_oc_if_else_different, code = E0308)]
     IfElseDifferent {
         #[primary_span]
         span: Span,
         #[subdiagnostic]
         subdiags: Vec<TypeErrorAdditionalDiags>,
     },
-    #[diag(infer_oc_no_else, code = "E0317")]
+    #[diag(infer_oc_no_else, code = E0317)]
     NoElse {
         #[primary_span]
         span: Span,
     },
-    #[diag(infer_oc_no_diverge, code = "E0308")]
+    #[diag(infer_oc_no_diverge, code = E0308)]
     NoDiverge {
         #[primary_span]
         span: Span,
         #[subdiagnostic]
         subdiags: Vec<TypeErrorAdditionalDiags>,
     },
-    #[diag(infer_oc_fn_main_correct_type, code = "E0580")]
+    #[diag(infer_oc_fn_main_correct_type, code = E0580)]
     FnMainCorrectType {
         #[primary_span]
         span: Span,
     },
-    #[diag(infer_oc_fn_start_correct_type, code = "E0308")]
+    #[diag(infer_oc_fn_start_correct_type, code = E0308)]
     FnStartCorrectType {
         #[primary_span]
         span: Span,
         #[subdiagnostic]
         subdiags: Vec<TypeErrorAdditionalDiags>,
     },
-    #[diag(infer_oc_fn_lang_correct_type, code = "E0308")]
+    #[diag(infer_oc_fn_lang_correct_type, code = E0308)]
     FnLangCorrectType {
         #[primary_span]
         span: Span,
@@ -1452,33 +1452,33 @@ pub enum ObligationCauseFailureCode {
         subdiags: Vec<TypeErrorAdditionalDiags>,
         lang_item_name: Symbol,
     },
-    #[diag(infer_oc_intrinsic_correct_type, code = "E0308")]
+    #[diag(infer_oc_intrinsic_correct_type, code = E0308)]
     IntrinsicCorrectType {
         #[primary_span]
         span: Span,
         #[subdiagnostic]
         subdiags: Vec<TypeErrorAdditionalDiags>,
     },
-    #[diag(infer_oc_method_correct_type, code = "E0308")]
+    #[diag(infer_oc_method_correct_type, code = E0308)]
     MethodCorrectType {
         #[primary_span]
         span: Span,
         #[subdiagnostic]
         subdiags: Vec<TypeErrorAdditionalDiags>,
     },
-    #[diag(infer_oc_closure_selfref, code = "E0644")]
+    #[diag(infer_oc_closure_selfref, code = E0644)]
     ClosureSelfref {
         #[primary_span]
         span: Span,
     },
-    #[diag(infer_oc_cant_coerce, code = "E0308")]
+    #[diag(infer_oc_cant_coerce, code = E0308)]
     CantCoerce {
         #[primary_span]
         span: Span,
         #[subdiagnostic]
         subdiags: Vec<TypeErrorAdditionalDiags>,
     },
-    #[diag(infer_oc_generic, code = "E0308")]
+    #[diag(infer_oc_generic, code = E0308)]
     Generic {
         #[primary_span]
         span: Span,
diff --git a/compiler/rustc_infer/src/infer/error_reporting/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
index 7882e761a0c..e19177fccef 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/mod.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
@@ -60,7 +60,7 @@
 
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_errors::{
-    error_code, pluralize, struct_span_code_err, Applicability, DiagCtxt, Diagnostic,
+    codes::*, pluralize, struct_span_code_err, Applicability, DiagCtxt, Diagnostic,
     DiagnosticBuilder, DiagnosticStyledString, ErrorGuaranteed, IntoDiagnosticArg,
 };
 use rustc_hir as hir;
@@ -2362,9 +2362,9 @@ pub fn construct_generic_bound_failure(
             .dcx()
             .struct_span_err(span, format!("{labeled_user_string} may not live long enough"));
         err.code(match sub.kind() {
-            ty::ReEarlyParam(_) | ty::ReLateParam(_) if sub.has_name() => error_code!(E0309),
-            ty::ReStatic => error_code!(E0310),
-            _ => error_code!(E0311),
+            ty::ReEarlyParam(_) | ty::ReLateParam(_) if sub.has_name() => E0309,
+            ty::ReStatic => E0310,
+            _ => E0311,
         });
 
         '_explain: {
diff --git a/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs b/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
index 03c8e08aa01..cf1e042c529 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
@@ -5,7 +5,7 @@
 use crate::infer::error_reporting::TypeErrCtxt;
 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use crate::infer::InferCtxt;
-use rustc_errors::{DiagnosticBuilder, IntoDiagnosticArg};
+use rustc_errors::{codes::*, DiagnosticBuilder, ErrCode, IntoDiagnosticArg};
 use rustc_hir as hir;
 use rustc_hir::def::Res;
 use rustc_hir::def::{CtorOf, DefKind, Namespace};
@@ -43,12 +43,12 @@ pub enum TypeAnnotationNeeded {
     E0284,
 }
 
-impl Into<String> for TypeAnnotationNeeded {
-    fn into(self) -> String {
+impl Into<ErrCode> for TypeAnnotationNeeded {
+    fn into(self) -> ErrCode {
         match self {
-            Self::E0282 => rustc_errors::error_code!(E0282),
-            Self::E0283 => rustc_errors::error_code!(E0283),
-            Self::E0284 => rustc_errors::error_code!(E0284),
+            Self::E0282 => E0282,
+            Self::E0283 => E0283,
+            Self::E0284 => E0284,
         }
     }
 }
diff --git a/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs b/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs
index 21ea48c6c83..0e7c641e0e0 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs
@@ -195,7 +195,7 @@ pub fn note_and_explain_type_err(
                             }
                         }
                         diag.help("type parameters must be constrained to match other types");
-                        if tcx.sess.teach(&diag.get_code().unwrap()) {
+                        if tcx.sess.teach(diag.get_code().unwrap()) {
                             diag.help(
                                 "given a type parameter `T` and a method `foo`:
 ```
@@ -678,7 +678,7 @@ fn expected_projection(
                  https://doc.rust-lang.org/book/ch19-03-advanced-traits.html",
             );
         }
-        if tcx.sess.teach(&diag.get_code().unwrap()) {
+        if tcx.sess.teach(diag.get_code().unwrap()) {
             diag.help(
                 "given an associated type `T` and a method `foo`:
 ```
diff --git a/compiler/rustc_infer/src/traits/error_reporting/mod.rs b/compiler/rustc_infer/src/traits/error_reporting/mod.rs
index 6f218019dee..eabc1b953af 100644
--- a/compiler/rustc_infer/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_infer/src/traits/error_reporting/mod.rs
@@ -2,7 +2,7 @@
 
 use crate::infer::InferCtxt;
 use rustc_data_structures::fx::FxIndexSet;
-use rustc_errors::{struct_span_code_err, Applicability, DiagnosticBuilder, MultiSpan};
+use rustc_errors::{codes::*, struct_span_code_err, Applicability, DiagnosticBuilder, MultiSpan};
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::intravisit::Map;
diff --git a/compiler/rustc_lint/src/errors.rs b/compiler/rustc_lint/src/errors.rs
index 841d282a099..3bd0c1b8031 100644
--- a/compiler/rustc_lint/src/errors.rs
+++ b/compiler/rustc_lint/src/errors.rs
@@ -1,11 +1,11 @@
 use crate::fluent_generated as fluent;
-use rustc_errors::{AddToDiagnostic, Diagnostic, SubdiagnosticMessage};
+use rustc_errors::{codes::*, AddToDiagnostic, Diagnostic, SubdiagnosticMessage};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_session::lint::Level;
 use rustc_span::{Span, Symbol};
 
 #[derive(Diagnostic)]
-#[diag(lint_overruled_attribute, code = "E0453")]
+#[diag(lint_overruled_attribute, code = E0453)]
 pub struct OverruledAttribute<'a> {
     #[primary_span]
     pub span: Span,
@@ -48,7 +48,7 @@ fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
 }
 
 #[derive(Diagnostic)]
-#[diag(lint_malformed_attribute, code = "E0452")]
+#[diag(lint_malformed_attribute, code = E0452)]
 pub struct MalformedAttribute {
     #[primary_span]
     pub span: Span,
@@ -67,7 +67,7 @@ pub enum MalformedAttributeSub {
 }
 
 #[derive(Diagnostic)]
-#[diag(lint_unknown_tool_in_scoped_lint, code = "E0710")]
+#[diag(lint_unknown_tool_in_scoped_lint, code = E0710)]
 pub struct UnknownToolInScopedLint {
     #[primary_span]
     pub span: Option<Span>,
@@ -78,7 +78,7 @@ pub struct UnknownToolInScopedLint {
 }
 
 #[derive(Diagnostic)]
-#[diag(lint_builtin_ellipsis_inclusive_range_patterns, code = "E0783")]
+#[diag(lint_builtin_ellipsis_inclusive_range_patterns, code = E0783)]
 pub struct BuiltinEllipsisInclusiveRangePatterns {
     #[primary_span]
     pub span: Span,
@@ -95,13 +95,13 @@ pub struct RequestedLevel<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(lint_unsupported_group, code = "E0602")]
+#[diag(lint_unsupported_group, code = E0602)]
 pub struct UnsupportedGroup {
     pub lint_group: String,
 }
 
 #[derive(Diagnostic)]
-#[diag(lint_check_name_unknown_tool, code = "E0602")]
+#[diag(lint_check_name_unknown_tool, code = E0602)]
 pub struct CheckNameUnknownTool<'a> {
     pub tool_name: Symbol,
     #[subdiagnostic]
diff --git a/compiler/rustc_lint/src/lints.rs b/compiler/rustc_lint/src/lints.rs
index e19bb1cb62f..f916deb4a46 100644
--- a/compiler/rustc_lint/src/lints.rs
+++ b/compiler/rustc_lint/src/lints.rs
@@ -5,8 +5,8 @@
 use crate::errors::RequestedLevel;
 use crate::fluent_generated as fluent;
 use rustc_errors::{
-    AddToDiagnostic, Applicability, DecorateLint, Diagnostic, DiagnosticBuilder, DiagnosticMessage,
-    DiagnosticStyledString, SubdiagnosticMessage, SuggestionStyle,
+    codes::*, AddToDiagnostic, Applicability, DecorateLint, Diagnostic, DiagnosticBuilder,
+    DiagnosticMessage, DiagnosticStyledString, SubdiagnosticMessage, SuggestionStyle,
 };
 use rustc_hir::def_id::DefId;
 use rustc_macros::{LintDiagnostic, Subdiagnostic};
@@ -1065,7 +1065,7 @@ pub enum UnknownLintSuggestion {
 }
 
 #[derive(LintDiagnostic)]
-#[diag(lint_unknown_lint, code = "E0602")]
+#[diag(lint_unknown_lint, code = E0602)]
 pub struct UnknownLintFromCommandLine<'a> {
     pub name: String,
     #[subdiagnostic]
diff --git a/compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs b/compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs
index 0b7ecff8148..85bb9584a05 100644
--- a/compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs
+++ b/compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs
@@ -209,9 +209,9 @@ fn generate_structure_code_for_attr(
                 if path.is_ident("code") {
                     self.code.set_once((), path.span().unwrap());
 
-                    let code = nested.parse::<syn::LitStr>()?;
+                    let code = nested.parse::<syn::Expr>()?;
                     tokens.extend(quote! {
-                        diag.code(#code.to_string());
+                        diag.code(#code);
                     });
                 } else {
                     span_err(path.span().unwrap(), "unknown argument")
diff --git a/compiler/rustc_macros/src/diagnostics/mod.rs b/compiler/rustc_macros/src/diagnostics/mod.rs
index 135b9e32fe7..33dffe6998a 100644
--- a/compiler/rustc_macros/src/diagnostics/mod.rs
+++ b/compiler/rustc_macros/src/diagnostics/mod.rs
@@ -20,7 +20,7 @@
 /// # extern crate rust_middle;
 /// # use rustc_middle::ty::Ty;
 /// #[derive(Diagnostic)]
-/// #[diag(borrowck_move_out_of_borrow, code = "E0505")]
+/// #[diag(borrowck_move_out_of_borrow, code = E0505)]
 /// pub struct MoveOutOfBorrowError<'tcx> {
 ///     pub name: Ident,
 ///     pub ty: Ty<'tcx>,
diff --git a/compiler/rustc_metadata/src/errors.rs b/compiler/rustc_metadata/src/errors.rs
index 27c26d31781..d17bf0cf708 100644
--- a/compiler/rustc_metadata/src/errors.rs
+++ b/compiler/rustc_metadata/src/errors.rs
@@ -4,7 +4,7 @@
 };
 
 use rustc_errors::{
-    error_code, DiagCtxt, DiagnosticBuilder, EmissionGuarantee, IntoDiagnostic, Level,
+    codes::*, DiagCtxt, DiagnosticBuilder, EmissionGuarantee, IntoDiagnostic, Level,
 };
 use rustc_macros::Diagnostic;
 use rustc_session::config;
@@ -122,7 +122,7 @@ pub struct WasmImportForm {
 }
 
 #[derive(Diagnostic)]
-#[diag(metadata_empty_link_name, code = "E0454")]
+#[diag(metadata_empty_link_name, code = E0454)]
 pub struct EmptyLinkName {
     #[primary_span]
     #[label]
@@ -130,21 +130,21 @@ pub struct EmptyLinkName {
 }
 
 #[derive(Diagnostic)]
-#[diag(metadata_link_framework_apple, code = "E0455")]
+#[diag(metadata_link_framework_apple, code = E0455)]
 pub struct LinkFrameworkApple {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(metadata_framework_only_windows, code = "E0455")]
+#[diag(metadata_framework_only_windows, code = E0455)]
 pub struct FrameworkOnlyWindows {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(metadata_unknown_link_kind, code = "E0458")]
+#[diag(metadata_unknown_link_kind, code = E0458)]
 pub struct UnknownLinkKind<'a> {
     #[primary_span]
     #[label]
@@ -239,7 +239,7 @@ pub struct IncompatibleWasmLink {
 }
 
 #[derive(Diagnostic)]
-#[diag(metadata_link_requires_name, code = "E0459")]
+#[diag(metadata_link_requires_name, code = E0459)]
 pub struct LinkRequiresName {
     #[primary_span]
     #[label]
@@ -502,7 +502,7 @@ fn into_diagnostic(self, dcx: &'_ DiagCtxt, level: Level) -> DiagnosticBuilder<'
         let mut diag = DiagnosticBuilder::new(dcx, level, fluent::metadata_multiple_candidates);
         diag.arg("crate_name", self.crate_name);
         diag.arg("flavor", self.flavor);
-        diag.code(error_code!(E0464));
+        diag.code(E0464);
         diag.span(self.span);
         for (i, candidate) in self.candidates.iter().enumerate() {
             diag.note(format!("candidate #{}: {}", i + 1, candidate.display()));
@@ -512,7 +512,7 @@ fn into_diagnostic(self, dcx: &'_ DiagCtxt, level: Level) -> DiagnosticBuilder<'
 }
 
 #[derive(Diagnostic)]
-#[diag(metadata_symbol_conflicts_current, code = "E0519")]
+#[diag(metadata_symbol_conflicts_current, code = E0519)]
 pub struct SymbolConflictsCurrent {
     #[primary_span]
     pub span: Span,
@@ -537,7 +537,7 @@ pub struct DlError {
 }
 
 #[derive(Diagnostic)]
-#[diag(metadata_newer_crate_version, code = "E0460")]
+#[diag(metadata_newer_crate_version, code = E0460)]
 #[note]
 #[note(metadata_found_crate_versions)]
 pub struct NewerCrateVersion {
@@ -549,7 +549,7 @@ pub struct NewerCrateVersion {
 }
 
 #[derive(Diagnostic)]
-#[diag(metadata_no_crate_with_triple, code = "E0461")]
+#[diag(metadata_no_crate_with_triple, code = E0461)]
 #[note(metadata_found_crate_versions)]
 pub struct NoCrateWithTriple<'a> {
     #[primary_span]
@@ -561,7 +561,7 @@ pub struct NoCrateWithTriple<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(metadata_found_staticlib, code = "E0462")]
+#[diag(metadata_found_staticlib, code = E0462)]
 #[note(metadata_found_crate_versions)]
 #[help]
 pub struct FoundStaticlib {
@@ -573,7 +573,7 @@ pub struct FoundStaticlib {
 }
 
 #[derive(Diagnostic)]
-#[diag(metadata_incompatible_rustc, code = "E0514")]
+#[diag(metadata_incompatible_rustc, code = E0514)]
 #[note(metadata_found_crate_versions)]
 #[help]
 pub struct IncompatibleRustc {
@@ -598,7 +598,7 @@ fn into_diagnostic(self, dcx: &'_ DiagCtxt, level: Level) -> DiagnosticBuilder<'
         let mut diag = DiagnosticBuilder::new(dcx, level, fluent::metadata_invalid_meta_files);
         diag.arg("crate_name", self.crate_name);
         diag.arg("add_info", self.add_info);
-        diag.code(error_code!(E0786));
+        diag.code(E0786);
         diag.span(self.span);
         for crate_rejection in self.crate_rejections {
             diag.note(crate_rejection);
@@ -627,7 +627,7 @@ fn into_diagnostic(self, dcx: &'_ DiagCtxt, level: Level) -> DiagnosticBuilder<'
         diag.arg("current_crate", self.current_crate);
         diag.arg("add_info", self.add_info);
         diag.arg("locator_triple", self.locator_triple.triple());
-        diag.code(error_code!(E0463));
+        diag.code(E0463);
         diag.span(self.span);
         if (self.crate_name == sym::std || self.crate_name == sym::core)
             && self.locator_triple != TargetTriple::from_triple(config::host_triple())
diff --git a/compiler/rustc_middle/src/error.rs b/compiler/rustc_middle/src/error.rs
index 3c553657087..e0436b38c4b 100644
--- a/compiler/rustc_middle/src/error.rs
+++ b/compiler/rustc_middle/src/error.rs
@@ -1,14 +1,14 @@
 use std::borrow::Cow;
 use std::fmt;
 
-use rustc_errors::{DiagnosticArgValue, DiagnosticMessage};
+use rustc_errors::{codes::*, DiagnosticArgValue, DiagnosticMessage};
 use rustc_macros::Diagnostic;
 use rustc_span::{Span, Symbol};
 
 use crate::ty::Ty;
 
 #[derive(Diagnostic)]
-#[diag(middle_drop_check_overflow, code = "E0320")]
+#[diag(middle_drop_check_overflow, code = E0320)]
 #[note]
 pub struct DropCheckOverflow<'tcx> {
     #[primary_span]
diff --git a/compiler/rustc_middle/src/values.rs b/compiler/rustc_middle/src/values.rs
index 6a03bf243eb..27b48f46e75 100644
--- a/compiler/rustc_middle/src/values.rs
+++ b/compiler/rustc_middle/src/values.rs
@@ -1,7 +1,7 @@
 use crate::dep_graph::dep_kinds;
 use crate::query::plumbing::CyclePlaceholder;
 use rustc_data_structures::fx::FxHashSet;
-use rustc_errors::{pluralize, struct_span_code_err, Applicability, MultiSpan};
+use rustc_errors::{codes::*, pluralize, struct_span_code_err, Applicability, MultiSpan};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_middle::ty::Representability;
diff --git a/compiler/rustc_mir_build/src/errors.rs b/compiler/rustc_mir_build/src/errors.rs
index e1b998b2471..6929c8040c5 100644
--- a/compiler/rustc_mir_build/src/errors.rs
+++ b/compiler/rustc_mir_build/src/errors.rs
@@ -1,7 +1,7 @@
 use crate::fluent_generated as fluent;
 use rustc_errors::DiagnosticArgValue;
 use rustc_errors::{
-    error_code, AddToDiagnostic, Applicability, DiagCtxt, Diagnostic, DiagnosticBuilder,
+    codes::*, AddToDiagnostic, Applicability, DiagCtxt, Diagnostic, DiagnosticBuilder,
     IntoDiagnostic, Level, MultiSpan, SubdiagnosticMessage,
 };
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
@@ -138,7 +138,7 @@ pub struct UnsafeOpInUnsafeFnCallToFunctionWithRequiresUnsafe<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_call_to_unsafe_fn_requires_unsafe, code = "E0133")]
+#[diag(mir_build_call_to_unsafe_fn_requires_unsafe, code = E0133)]
 #[note]
 pub struct CallToUnsafeFunctionRequiresUnsafe<'a> {
     #[primary_span]
@@ -150,7 +150,7 @@ pub struct CallToUnsafeFunctionRequiresUnsafe<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_call_to_unsafe_fn_requires_unsafe_nameless, code = "E0133")]
+#[diag(mir_build_call_to_unsafe_fn_requires_unsafe_nameless, code = E0133)]
 #[note]
 pub struct CallToUnsafeFunctionRequiresUnsafeNameless {
     #[primary_span]
@@ -161,7 +161,7 @@ pub struct CallToUnsafeFunctionRequiresUnsafeNameless {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_call_to_unsafe_fn_requires_unsafe_unsafe_op_in_unsafe_fn_allowed, code = "E0133")]
+#[diag(mir_build_call_to_unsafe_fn_requires_unsafe_unsafe_op_in_unsafe_fn_allowed, code = E0133)]
 #[note]
 pub struct CallToUnsafeFunctionRequiresUnsafeUnsafeOpInUnsafeFnAllowed<'a> {
     #[primary_span]
@@ -175,7 +175,7 @@ pub struct CallToUnsafeFunctionRequiresUnsafeUnsafeOpInUnsafeFnAllowed<'a> {
 #[derive(Diagnostic)]
 #[diag(
     mir_build_call_to_unsafe_fn_requires_unsafe_nameless_unsafe_op_in_unsafe_fn_allowed,
-    code = "E0133"
+    code = E0133
 )]
 #[note]
 pub struct CallToUnsafeFunctionRequiresUnsafeNamelessUnsafeOpInUnsafeFnAllowed {
@@ -187,7 +187,7 @@ pub struct CallToUnsafeFunctionRequiresUnsafeNamelessUnsafeOpInUnsafeFnAllowed {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_inline_assembly_requires_unsafe, code = "E0133")]
+#[diag(mir_build_inline_assembly_requires_unsafe, code = E0133)]
 #[note]
 pub struct UseOfInlineAssemblyRequiresUnsafe {
     #[primary_span]
@@ -198,7 +198,7 @@ pub struct UseOfInlineAssemblyRequiresUnsafe {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_inline_assembly_requires_unsafe_unsafe_op_in_unsafe_fn_allowed, code = "E0133")]
+#[diag(mir_build_inline_assembly_requires_unsafe_unsafe_op_in_unsafe_fn_allowed, code = E0133)]
 #[note]
 pub struct UseOfInlineAssemblyRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
     #[primary_span]
@@ -209,7 +209,7 @@ pub struct UseOfInlineAssemblyRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_initializing_type_with_requires_unsafe, code = "E0133")]
+#[diag(mir_build_initializing_type_with_requires_unsafe, code = E0133)]
 #[note]
 pub struct InitializingTypeWithRequiresUnsafe {
     #[primary_span]
@@ -222,7 +222,7 @@ pub struct InitializingTypeWithRequiresUnsafe {
 #[derive(Diagnostic)]
 #[diag(
     mir_build_initializing_type_with_requires_unsafe_unsafe_op_in_unsafe_fn_allowed,
-    code = "E0133"
+    code = E0133
 )]
 #[note]
 pub struct InitializingTypeWithRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
@@ -234,7 +234,7 @@ pub struct InitializingTypeWithRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_mutable_static_requires_unsafe, code = "E0133")]
+#[diag(mir_build_mutable_static_requires_unsafe, code = E0133)]
 #[note]
 pub struct UseOfMutableStaticRequiresUnsafe {
     #[primary_span]
@@ -245,7 +245,7 @@ pub struct UseOfMutableStaticRequiresUnsafe {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_mutable_static_requires_unsafe_unsafe_op_in_unsafe_fn_allowed, code = "E0133")]
+#[diag(mir_build_mutable_static_requires_unsafe_unsafe_op_in_unsafe_fn_allowed, code = E0133)]
 #[note]
 pub struct UseOfMutableStaticRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
     #[primary_span]
@@ -256,7 +256,7 @@ pub struct UseOfMutableStaticRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_extern_static_requires_unsafe, code = "E0133")]
+#[diag(mir_build_extern_static_requires_unsafe, code = E0133)]
 #[note]
 pub struct UseOfExternStaticRequiresUnsafe {
     #[primary_span]
@@ -267,7 +267,7 @@ pub struct UseOfExternStaticRequiresUnsafe {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_extern_static_requires_unsafe_unsafe_op_in_unsafe_fn_allowed, code = "E0133")]
+#[diag(mir_build_extern_static_requires_unsafe_unsafe_op_in_unsafe_fn_allowed, code = E0133)]
 #[note]
 pub struct UseOfExternStaticRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
     #[primary_span]
@@ -278,7 +278,7 @@ pub struct UseOfExternStaticRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_deref_raw_pointer_requires_unsafe, code = "E0133")]
+#[diag(mir_build_deref_raw_pointer_requires_unsafe, code = E0133)]
 #[note]
 pub struct DerefOfRawPointerRequiresUnsafe {
     #[primary_span]
@@ -289,7 +289,7 @@ pub struct DerefOfRawPointerRequiresUnsafe {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_deref_raw_pointer_requires_unsafe_unsafe_op_in_unsafe_fn_allowed, code = "E0133")]
+#[diag(mir_build_deref_raw_pointer_requires_unsafe_unsafe_op_in_unsafe_fn_allowed, code = E0133)]
 #[note]
 pub struct DerefOfRawPointerRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
     #[primary_span]
@@ -300,7 +300,7 @@ pub struct DerefOfRawPointerRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_union_field_requires_unsafe, code = "E0133")]
+#[diag(mir_build_union_field_requires_unsafe, code = E0133)]
 #[note]
 pub struct AccessToUnionFieldRequiresUnsafe {
     #[primary_span]
@@ -311,7 +311,7 @@ pub struct AccessToUnionFieldRequiresUnsafe {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_union_field_requires_unsafe_unsafe_op_in_unsafe_fn_allowed, code = "E0133")]
+#[diag(mir_build_union_field_requires_unsafe_unsafe_op_in_unsafe_fn_allowed, code = E0133)]
 #[note]
 pub struct AccessToUnionFieldRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
     #[primary_span]
@@ -322,7 +322,7 @@ pub struct AccessToUnionFieldRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_mutation_of_layout_constrained_field_requires_unsafe, code = "E0133")]
+#[diag(mir_build_mutation_of_layout_constrained_field_requires_unsafe, code = E0133)]
 #[note]
 pub struct MutationOfLayoutConstrainedFieldRequiresUnsafe {
     #[primary_span]
@@ -335,7 +335,7 @@ pub struct MutationOfLayoutConstrainedFieldRequiresUnsafe {
 #[derive(Diagnostic)]
 #[diag(
     mir_build_mutation_of_layout_constrained_field_requires_unsafe_unsafe_op_in_unsafe_fn_allowed,
-    code = "E0133"
+    code = E0133
 )]
 #[note]
 pub struct MutationOfLayoutConstrainedFieldRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
@@ -347,7 +347,7 @@ pub struct MutationOfLayoutConstrainedFieldRequiresUnsafeUnsafeOpInUnsafeFnAllow
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_borrow_of_layout_constrained_field_requires_unsafe, code = "E0133")]
+#[diag(mir_build_borrow_of_layout_constrained_field_requires_unsafe, code = E0133)]
 #[note]
 pub struct BorrowOfLayoutConstrainedFieldRequiresUnsafe {
     #[primary_span]
@@ -360,7 +360,7 @@ pub struct BorrowOfLayoutConstrainedFieldRequiresUnsafe {
 #[derive(Diagnostic)]
 #[diag(
     mir_build_borrow_of_layout_constrained_field_requires_unsafe_unsafe_op_in_unsafe_fn_allowed,
-    code = "E0133"
+    code = E0133
 )]
 #[note]
 pub struct BorrowOfLayoutConstrainedFieldRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
@@ -372,7 +372,7 @@ pub struct BorrowOfLayoutConstrainedFieldRequiresUnsafeUnsafeOpInUnsafeFnAllowed
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_call_to_fn_with_requires_unsafe, code = "E0133")]
+#[diag(mir_build_call_to_fn_with_requires_unsafe, code = E0133)]
 #[help]
 pub struct CallToFunctionWithRequiresUnsafe<'a> {
     #[primary_span]
@@ -390,7 +390,7 @@ pub struct CallToFunctionWithRequiresUnsafe<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_call_to_fn_with_requires_unsafe_unsafe_op_in_unsafe_fn_allowed, code = "E0133")]
+#[diag(mir_build_call_to_fn_with_requires_unsafe_unsafe_op_in_unsafe_fn_allowed, code = E0133)]
 #[help]
 pub struct CallToFunctionWithRequiresUnsafeUnsafeOpInUnsafeFnAllowed<'a> {
     #[primary_span]
@@ -468,7 +468,7 @@ fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> DiagnosticBuilder<'
             fluent::mir_build_non_exhaustive_patterns_type_not_empty,
         );
         diag.span(self.span);
-        diag.code(error_code!(E0004));
+        diag.code(E0004);
         let peeled_ty = self.ty.peel_refs();
         diag.arg("ty", self.ty);
         diag.arg("peeled_ty", peeled_ty);
@@ -539,28 +539,28 @@ fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> DiagnosticBuilder<'
 pub struct NonExhaustiveMatchAllArmsGuarded;
 
 #[derive(Diagnostic)]
-#[diag(mir_build_static_in_pattern, code = "E0158")]
+#[diag(mir_build_static_in_pattern, code = E0158)]
 pub struct StaticInPattern {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_assoc_const_in_pattern, code = "E0158")]
+#[diag(mir_build_assoc_const_in_pattern, code = E0158)]
 pub struct AssocConstInPattern {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_const_param_in_pattern, code = "E0158")]
+#[diag(mir_build_const_param_in_pattern, code = E0158)]
 pub struct ConstParamInPattern {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_non_const_path, code = "E0080")]
+#[diag(mir_build_non_const_path, code = E0080)]
 pub struct NonConstPath {
     #[primary_span]
     pub span: Span,
@@ -590,7 +590,7 @@ pub struct CouldNotEvalConstPattern {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_lower_range_bound_must_be_less_than_or_equal_to_upper, code = "E0030")]
+#[diag(mir_build_lower_range_bound_must_be_less_than_or_equal_to_upper, code = E0030)]
 pub struct LowerRangeBoundMustBeLessThanOrEqualToUpper {
     #[primary_span]
     #[label]
@@ -611,7 +611,7 @@ pub struct LiteralOutOfRange<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_lower_range_bound_must_be_less_than_upper, code = "E0579")]
+#[diag(mir_build_lower_range_bound_must_be_less_than_upper, code = E0579)]
 pub struct LowerRangeBoundMustBeLessThanUpper {
     #[primary_span]
     pub span: Span,
@@ -634,7 +634,7 @@ pub struct TrailingIrrefutableLetPatterns {
 }
 
 #[derive(LintDiagnostic)]
-#[diag(mir_build_bindings_with_variant_name, code = "E0170")]
+#[diag(mir_build_bindings_with_variant_name, code = E0170)]
 pub struct BindingsWithVariantName {
     #[suggestion(code = "{ty_path}::{name}", applicability = "machine-applicable")]
     pub suggestion: Option<Span>,
@@ -821,7 +821,7 @@ pub struct NonPartialEqMatch<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_pattern_not_covered, code = "E0005")]
+#[diag(mir_build_pattern_not_covered, code = E0005)]
 pub(crate) struct PatternNotCovered<'s, 'tcx> {
     #[primary_span]
     pub span: Span,
diff --git a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
index 435ea3dc3bb..caf7f4227db 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
@@ -11,7 +11,7 @@
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_errors::{
-    struct_span_code_err, Applicability, DiagnosticBuilder, ErrorGuaranteed, MultiSpan,
+    codes::*, struct_span_code_err, Applicability, DiagnosticBuilder, ErrorGuaranteed, MultiSpan,
 };
 use rustc_hir as hir;
 use rustc_hir::def::*;
diff --git a/compiler/rustc_mir_build/src/thir/pattern/mod.rs b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
index ff7e985bdfd..2190ad14b55 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/mod.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
@@ -8,7 +8,7 @@
 use crate::errors::*;
 use crate::thir::util::UserAnnotatedTyHelpers;
 
-use rustc_errors::error_code;
+use rustc_errors::codes::*;
 use rustc_hir as hir;
 use rustc_hir::def::{CtorOf, DefKind, Res};
 use rustc_hir::pat_util::EnumerateAndAdjustIterator;
@@ -209,7 +209,7 @@ fn lower_pattern_range(
                     RangeEnd::Included => {
                         self.tcx.dcx().emit_err(LowerRangeBoundMustBeLessThanOrEqualToUpper {
                             span,
-                            teach: self.tcx.sess.teach(&error_code!(E0030)).then_some(()),
+                            teach: self.tcx.sess.teach(E0030).then_some(()),
                         })
                     }
                     RangeEnd::Excluded => {
diff --git a/compiler/rustc_mir_transform/src/errors.rs b/compiler/rustc_mir_transform/src/errors.rs
index 4574cb4d28d..4ef3d47d6a6 100644
--- a/compiler/rustc_mir_transform/src/errors.rs
+++ b/compiler/rustc_mir_transform/src/errors.rs
@@ -1,7 +1,7 @@
 use std::borrow::Cow;
 
 use rustc_errors::{
-    Applicability, DecorateLint, DiagCtxt, DiagnosticArgValue, DiagnosticBuilder,
+    codes::*, Applicability, DecorateLint, DiagCtxt, DiagnosticArgValue, DiagnosticBuilder,
     DiagnosticMessage, EmissionGuarantee, IntoDiagnostic, Level,
 };
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
@@ -33,7 +33,7 @@ pub(crate) enum ConstMutate {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_transform_unaligned_packed_ref, code = "E0793")]
+#[diag(mir_transform_unaligned_packed_ref, code = E0793)]
 #[note]
 #[note(mir_transform_note_ub)]
 #[help]
@@ -66,7 +66,7 @@ impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for RequiresUnsafe {
     #[track_caller]
     fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> DiagnosticBuilder<'a, G> {
         let mut diag = DiagnosticBuilder::new(dcx, level, fluent::mir_transform_requires_unsafe);
-        diag.code("E0133".to_string());
+        diag.code(E0133);
         diag.span(self.span);
         diag.span_label(self.span, self.details.label());
         let desc = dcx.eagerly_translate_to_string(self.details.label(), [].into_iter());
diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
index 40852048293..053a9c03d74 100644
--- a/compiler/rustc_parse/src/errors.rs
+++ b/compiler/rustc_parse/src/errors.rs
@@ -3,7 +3,7 @@
 use rustc_ast::token::Token;
 use rustc_ast::{Path, Visibility};
 use rustc_errors::{
-    AddToDiagnostic, Applicability, DiagCtxt, DiagnosticBuilder, IntoDiagnostic, Level,
+    codes::*, AddToDiagnostic, Applicability, DiagCtxt, DiagnosticBuilder, IntoDiagnostic, Level,
     SubdiagnosticMessage,
 };
 use rustc_macros::{Diagnostic, Subdiagnostic};
@@ -25,7 +25,7 @@ pub(crate) struct AmbiguousPlus {
 }
 
 #[derive(Diagnostic)]
-#[diag(parse_maybe_recover_from_bad_type_plus, code = "E0178")]
+#[diag(parse_maybe_recover_from_bad_type_plus, code = E0178)]
 pub(crate) struct BadTypePlus {
     pub ty: String,
     #[primary_span]
@@ -807,7 +807,7 @@ pub(crate) struct InclusiveRangeMatchArrow {
 }
 
 #[derive(Diagnostic)]
-#[diag(parse_inclusive_range_no_end, code = "E0586")]
+#[diag(parse_inclusive_range_no_end, code = E0586)]
 #[note]
 pub(crate) struct InclusiveRangeNoEnd {
     #[primary_span]
@@ -901,7 +901,7 @@ pub(crate) struct MismatchedClosingDelimiter {
 }
 
 #[derive(Diagnostic)]
-#[diag(parse_incorrect_visibility_restriction, code = "E0704")]
+#[diag(parse_incorrect_visibility_restriction, code = E0704)]
 #[help]
 pub(crate) struct IncorrectVisibilityRestriction {
     #[primary_span]
@@ -925,7 +925,7 @@ pub(crate) struct ExpectedStatementAfterOuterAttr {
 }
 
 #[derive(Diagnostic)]
-#[diag(parse_doc_comment_does_not_document_anything, code = "E0585")]
+#[diag(parse_doc_comment_does_not_document_anything, code = E0585)]
 #[help]
 pub(crate) struct DocCommentDoesNotDocumentAnything {
     #[primary_span]
@@ -1357,7 +1357,7 @@ pub(crate) struct AttributeOnParamType {
 }
 
 #[derive(Diagnostic)]
-#[diag(parse_pattern_method_param_without_body, code = "E0642")]
+#[diag(parse_pattern_method_param_without_body, code = E0642)]
 pub(crate) struct PatternMethodParamWithoutBody {
     #[primary_span]
     #[suggestion(code = "_", applicability = "machine-applicable")]
@@ -1565,7 +1565,7 @@ pub(crate) struct WhereClauseBeforeTupleStructBodySugg {
 }
 
 #[derive(Diagnostic)]
-#[diag(parse_async_fn_in_2015, code = "E0670")]
+#[diag(parse_async_fn_in_2015, code = E0670)]
 pub(crate) struct AsyncFnIn2015 {
     #[primary_span]
     #[label]
@@ -1929,7 +1929,7 @@ pub struct CrDocComment {
 }
 
 #[derive(Diagnostic)]
-#[diag(parse_no_digits_literal, code = "E0768")]
+#[diag(parse_no_digits_literal, code = E0768)]
 pub struct NoDigitsLiteral {
     #[primary_span]
     pub span: Span,
@@ -2499,7 +2499,7 @@ pub(crate) struct FnPointerCannotBeAsync {
 }
 
 #[derive(Diagnostic)]
-#[diag(parse_nested_c_variadic_type, code = "E0743")]
+#[diag(parse_nested_c_variadic_type, code = E0743)]
 pub(crate) struct NestedCVariadicType {
     #[primary_span]
     pub span: Span,
diff --git a/compiler/rustc_parse/src/lexer/mod.rs b/compiler/rustc_parse/src/lexer/mod.rs
index 20ec4a300c1..31552452676 100644
--- a/compiler/rustc_parse/src/lexer/mod.rs
+++ b/compiler/rustc_parse/src/lexer/mod.rs
@@ -7,7 +7,7 @@
 use rustc_ast::token::{self, CommentKind, Delimiter, Token, TokenKind};
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::util::unicode::contains_text_flow_control_chars;
-use rustc_errors::{error_code, Applicability, DiagCtxt, DiagnosticBuilder, StashKey};
+use rustc_errors::{codes::*, Applicability, DiagCtxt, DiagnosticBuilder, StashKey};
 use rustc_lexer::unescape::{self, EscapeError, Mode};
 use rustc_lexer::{Base, DocStyle, RawStrError};
 use rustc_lexer::{Cursor, LiteralKind};
@@ -397,7 +397,7 @@ fn cook_lexer_literal(
                 if !terminated {
                     self.dcx()
                         .struct_span_fatal(self.mk_sp(start, end), "unterminated character literal")
-                        .with_code(error_code!(E0762))
+                        .with_code(E0762)
                         .emit()
                 }
                 self.cook_unicode(token::Char, Mode::Char, start, end, 1, 1) // ' '
@@ -409,7 +409,7 @@ fn cook_lexer_literal(
                             self.mk_sp(start + BytePos(1), end),
                             "unterminated byte constant",
                         )
-                        .with_code(error_code!(E0763))
+                        .with_code(E0763)
                         .emit()
                 }
                 self.cook_unicode(token::Byte, Mode::Byte, start, end, 2, 1) // b' '
@@ -421,7 +421,7 @@ fn cook_lexer_literal(
                             self.mk_sp(start, end),
                             "unterminated double quote string",
                         )
-                        .with_code(error_code!(E0765))
+                        .with_code(E0765)
                         .emit()
                 }
                 self.cook_unicode(token::Str, Mode::Str, start, end, 1, 1) // " "
@@ -433,7 +433,7 @@ fn cook_lexer_literal(
                             self.mk_sp(start + BytePos(1), end),
                             "unterminated double quote byte string",
                         )
-                        .with_code(error_code!(E0766))
+                        .with_code(E0766)
                         .emit()
                 }
                 self.cook_unicode(token::ByteStr, Mode::ByteStr, start, end, 2, 1) // b" "
@@ -445,7 +445,7 @@ fn cook_lexer_literal(
                             self.mk_sp(start + BytePos(1), end),
                             "unterminated C string",
                         )
-                        .with_code(error_code!(E0767))
+                        .with_code(E0767)
                         .emit()
                 }
                 self.cook_mixed(token::CStr, Mode::CStr, start, end, 2, 1) // c" "
@@ -582,7 +582,7 @@ fn report_unterminated_raw_string(
     ) -> ! {
         let mut err =
             self.dcx().struct_span_fatal(self.mk_sp(start, start), "unterminated raw string");
-        err.code(error_code!(E0748));
+        err.code(E0748);
         err.span_label(self.mk_sp(start, start), "unterminated raw string");
 
         if n_hashes > 0 {
@@ -614,7 +614,7 @@ fn report_unterminated_block_comment(&self, start: BytePos, doc_style: Option<Do
         };
         let last_bpos = self.pos;
         let mut err = self.dcx().struct_span_fatal(self.mk_sp(start, last_bpos), msg);
-        err.code(error_code!(E0758));
+        err.code(E0758);
         let mut nested_block_comment_open_idxs = vec![];
         let mut last_nested_block_comment_idxs = None;
         let mut content_chars = self.str_from(start).char_indices().peekable();
diff --git a/compiler/rustc_parse/src/parser/attr.rs b/compiler/rustc_parse/src/parser/attr.rs
index a92609c2c2f..98e062dd784 100644
--- a/compiler/rustc_parse/src/parser/attr.rs
+++ b/compiler/rustc_parse/src/parser/attr.rs
@@ -8,7 +8,7 @@
 use rustc_ast as ast;
 use rustc_ast::attr;
 use rustc_ast::token::{self, Delimiter, Nonterminal};
-use rustc_errors::{error_code, Diagnostic, PResult};
+use rustc_errors::{codes::*, Diagnostic, PResult};
 use rustc_span::{sym, BytePos, Span};
 use thin_vec::ThinVec;
 use tracing::debug;
@@ -61,7 +61,7 @@ pub(super) fn parse_outer_attributes(&mut self) -> PResult<'a, AttrWrapper> {
                     let mut err = self
                         .dcx()
                         .struct_span_err(span, fluent::parse_inner_doc_comment_not_permitted);
-                    err.code(error_code!(E0753));
+                    err.code(E0753);
                     if let Some(replacement_span) = self.annotate_following_item_if_applicable(
                         &mut err,
                         span,
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index 3bd8ae02586..9a77643f951 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -10,7 +10,7 @@
 use rustc_ast::util::case::Case;
 use rustc_ast::{self as ast};
 use rustc_ast_pretty::pprust;
-use rustc_errors::{struct_span_code_err, Applicability, PResult, StashKey};
+use rustc_errors::{codes::*, struct_span_code_err, Applicability, PResult, StashKey};
 use rustc_span::edit_distance::edit_distance;
 use rustc_span::edition::Edition;
 use rustc_span::source_map;
diff --git a/compiler/rustc_passes/src/entry.rs b/compiler/rustc_passes/src/entry.rs
index 25ca685cbfa..97c70e327f0 100644
--- a/compiler/rustc_passes/src/entry.rs
+++ b/compiler/rustc_passes/src/entry.rs
@@ -1,6 +1,6 @@
 use rustc_ast::attr;
 use rustc_ast::entry::EntryPointType;
-use rustc_errors::error_code;
+use rustc_errors::codes::*;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_ID, LOCAL_CRATE};
 use rustc_hir::{ItemId, Node, CRATE_HIR_ID};
@@ -180,8 +180,8 @@ fn no_main_err(tcx: TyCtxt<'_>, visitor: &EntryContext<'_>) {
         Default::default()
     });
     let main_def_opt = tcx.resolutions(()).main_def;
-    let code = error_code!(E0601);
-    let add_teach_note = tcx.sess.teach(&code);
+    let code = E0601;
+    let add_teach_note = tcx.sess.teach(code);
     // The file may be empty, which leads to the diagnostic machinery not emitting this
     // note. This is a relatively simple way to detect that case and emit a span-less
     // note instead.
diff --git a/compiler/rustc_passes/src/errors.rs b/compiler/rustc_passes/src/errors.rs
index cf3c7cc4ace..77bfe57e370 100644
--- a/compiler/rustc_passes/src/errors.rs
+++ b/compiler/rustc_passes/src/errors.rs
@@ -6,7 +6,7 @@
 use crate::fluent_generated as fluent;
 use rustc_ast::Label;
 use rustc_errors::{
-    error_code, AddToDiagnostic, Applicability, DiagCtxt, Diagnostic, DiagnosticBuilder,
+    codes::*, AddToDiagnostic, Applicability, DiagCtxt, Diagnostic, DiagnosticBuilder,
     DiagnosticSymbolList, EmissionGuarantee, IntoDiagnostic, Level, MultiSpan,
 };
 use rustc_hir::{self as hir, ExprKind, Target};
@@ -55,7 +55,7 @@ pub struct IgnoredAttr<'a> {
 pub struct IgnoredInlineAttrConstants;
 
 #[derive(Diagnostic)]
-#[diag(passes_inline_not_fn_or_closure, code = "E0518")]
+#[diag(passes_inline_not_fn_or_closure, code = E0518)]
 pub struct InlineNotFnOrClosure {
     #[primary_span]
     pub attr_span: Span,
@@ -76,7 +76,7 @@ pub struct InlineNotFnOrClosure {
 pub struct IgnoredCoverageFnDefn;
 
 #[derive(Diagnostic)]
-#[diag(passes_coverage_not_coverable, code = "E0788")]
+#[diag(passes_coverage_not_coverable, code = E0788)]
 pub struct IgnoredCoverageNotCoverable {
     #[primary_span]
     pub attr_span: Span,
@@ -95,14 +95,14 @@ pub struct AttrShouldBeAppliedToFn {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_naked_tracked_caller, code = "E0736")]
+#[diag(passes_naked_tracked_caller, code = E0736)]
 pub struct NakedTrackedCaller {
     #[primary_span]
     pub attr_span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_should_be_applied_to_fn, code = "E0739")]
+#[diag(passes_should_be_applied_to_fn, code = E0739)]
 pub struct TrackedCallerWrongLocation {
     #[primary_span]
     pub attr_span: Span,
@@ -112,7 +112,7 @@ pub struct TrackedCallerWrongLocation {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_should_be_applied_to_struct_enum, code = "E0701")]
+#[diag(passes_should_be_applied_to_struct_enum, code = E0701)]
 pub struct NonExhaustiveWrongLocation {
     #[primary_span]
     pub attr_span: Span,
@@ -370,28 +370,28 @@ pub struct HasIncoherentInherentImpl {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_both_ffi_const_and_pure, code = "E0757")]
+#[diag(passes_both_ffi_const_and_pure, code = E0757)]
 pub struct BothFfiConstAndPure {
     #[primary_span]
     pub attr_span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_ffi_pure_invalid_target, code = "E0755")]
+#[diag(passes_ffi_pure_invalid_target, code = E0755)]
 pub struct FfiPureInvalidTarget {
     #[primary_span]
     pub attr_span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_ffi_const_invalid_target, code = "E0756")]
+#[diag(passes_ffi_const_invalid_target, code = E0756)]
 pub struct FfiConstInvalidTarget {
     #[primary_span]
     pub attr_span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_ffi_returns_twice_invalid_target, code = "E0724")]
+#[diag(passes_ffi_returns_twice_invalid_target, code = E0724)]
 pub struct FfiReturnsTwiceInvalidTarget {
     #[primary_span]
     pub attr_span: Span,
@@ -552,21 +552,21 @@ pub struct NoMangle {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_repr_ident, code = "E0565")]
+#[diag(passes_repr_ident, code = E0565)]
 pub struct ReprIdent {
     #[primary_span]
     pub span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_repr_conflicting, code = "E0566")]
+#[diag(passes_repr_conflicting, code = E0566)]
 pub struct ReprConflicting {
     #[primary_span]
     pub hint_spans: Vec<Span>,
 }
 
 #[derive(LintDiagnostic)]
-#[diag(passes_repr_conflicting, code = "E0566")]
+#[diag(passes_repr_conflicting, code = E0566)]
 pub struct ReprConflictingLint;
 
 #[derive(Diagnostic)]
@@ -667,7 +667,7 @@ pub(crate) struct EmptyConfusables {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_incorrect_meta_item, code = "E0539")]
+#[diag(passes_incorrect_meta_item, code = E0539)]
 pub(crate) struct IncorrectMetaItem {
     #[primary_span]
     pub span: Span,
@@ -737,7 +737,7 @@ pub struct Unused {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_non_exported_macro_invalid_attrs, code = "E0518")]
+#[diag(passes_non_exported_macro_invalid_attrs, code = E0518)]
 pub struct NonExportedMacroInvalidAttrs {
     #[primary_span]
     #[label]
@@ -801,7 +801,7 @@ pub struct DeprecatedAnnotationHasNoEffect {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_unknown_external_lang_item, code = "E0264")]
+#[diag(passes_unknown_external_lang_item, code = E0264)]
 pub struct UnknownExternLangItem {
     #[primary_span]
     pub span: Span,
@@ -837,7 +837,7 @@ pub struct LangItemWithTargetFeature {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_lang_item_on_incorrect_target, code = "E0718")]
+#[diag(passes_lang_item_on_incorrect_target, code = E0718)]
 pub struct LangItemOnIncorrectTarget {
     #[primary_span]
     #[label]
@@ -848,7 +848,7 @@ pub struct LangItemOnIncorrectTarget {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_unknown_lang_item, code = "E0522")]
+#[diag(passes_unknown_lang_item, code = E0522)]
 pub struct UnknownLangItem {
     #[primary_span]
     #[label]
@@ -990,7 +990,7 @@ pub struct UnrecognizedField {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_feature_stable_twice, code = "E0711")]
+#[diag(passes_feature_stable_twice, code = E0711)]
 pub struct FeatureStableTwice {
     #[primary_span]
     pub span: Span,
@@ -1000,7 +1000,7 @@ pub struct FeatureStableTwice {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_feature_previously_declared, code = "E0711")]
+#[diag(passes_feature_previously_declared, code = E0711)]
 pub struct FeaturePreviouslyDeclared<'a, 'b> {
     #[primary_span]
     pub span: Span,
@@ -1025,7 +1025,7 @@ impl<'a, G: EmissionGuarantee> IntoDiagnostic<'_, G> for BreakNonLoop<'a> {
     fn into_diagnostic(self, dcx: &DiagCtxt, level: Level) -> DiagnosticBuilder<'_, G> {
         let mut diag = DiagnosticBuilder::new(dcx, level, fluent::passes_break_non_loop);
         diag.span(self.span);
-        diag.code(error_code!(E0571));
+        diag.code(E0571);
         diag.arg("kind", self.kind);
         diag.span_label(self.span, fluent::passes_label);
         if let Some(head) = self.head {
@@ -1063,7 +1063,7 @@ fn into_diagnostic(self, dcx: &DiagCtxt, level: Level) -> DiagnosticBuilder<'_,
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_continue_labeled_block, code = "E0696")]
+#[diag(passes_continue_labeled_block, code = E0696)]
 pub struct ContinueLabeledBlock {
     #[primary_span]
     #[label]
@@ -1073,7 +1073,7 @@ pub struct ContinueLabeledBlock {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_break_inside_closure, code = "E0267")]
+#[diag(passes_break_inside_closure, code = E0267)]
 pub struct BreakInsideClosure<'a> {
     #[primary_span]
     #[label]
@@ -1084,7 +1084,7 @@ pub struct BreakInsideClosure<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_break_inside_async_block, code = "E0267")]
+#[diag(passes_break_inside_async_block, code = E0267)]
 pub struct BreakInsideAsyncBlock<'a> {
     #[primary_span]
     #[label]
@@ -1095,7 +1095,7 @@ pub struct BreakInsideAsyncBlock<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_outside_loop, code = "E0268")]
+#[diag(passes_outside_loop, code = E0268)]
 pub struct OutsideLoop<'a> {
     #[primary_span]
     #[label]
@@ -1115,7 +1115,7 @@ pub struct OutsideLoopSuggestion {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_unlabeled_in_labeled_block, code = "E0695")]
+#[diag(passes_unlabeled_in_labeled_block, code = E0695)]
 pub struct UnlabeledInLabeledBlock<'a> {
     #[primary_span]
     #[label]
@@ -1124,7 +1124,7 @@ pub struct UnlabeledInLabeledBlock<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_unlabeled_cf_in_while_condition, code = "E0590")]
+#[diag(passes_unlabeled_cf_in_while_condition, code = E0590)]
 pub struct UnlabeledCfInWhileCondition<'a> {
     #[primary_span]
     #[label]
@@ -1169,7 +1169,7 @@ impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for NakedFunctionsAsmBlock {
     fn into_diagnostic(self, dcx: &DiagCtxt, level: Level) -> DiagnosticBuilder<'_, G> {
         let mut diag = DiagnosticBuilder::new(dcx, level, fluent::passes_naked_functions_asm_block);
         diag.span(self.span);
-        diag.code(error_code!(E0787));
+        diag.code(E0787);
         for span in self.multiple_asms.iter() {
             diag.span_label(*span, fluent::passes_label_multiple_asm);
         }
@@ -1181,14 +1181,14 @@ fn into_diagnostic(self, dcx: &DiagCtxt, level: Level) -> DiagnosticBuilder<'_,
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_naked_functions_operands, code = "E0787")]
+#[diag(passes_naked_functions_operands, code = E0787)]
 pub struct NakedFunctionsOperands {
     #[primary_span]
     pub unsupported_operands: Vec<Span>,
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_naked_functions_asm_options, code = "E0787")]
+#[diag(passes_naked_functions_asm_options, code = E0787)]
 pub struct NakedFunctionsAsmOptions {
     #[primary_span]
     pub span: Span,
@@ -1196,7 +1196,7 @@ pub struct NakedFunctionsAsmOptions {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_naked_functions_must_use_noreturn, code = "E0787")]
+#[diag(passes_naked_functions_must_use_noreturn, code = E0787)]
 pub struct NakedFunctionsMustUseNoreturn {
     #[primary_span]
     pub span: Span,
@@ -1229,7 +1229,7 @@ pub struct AttrOnlyInFunctions {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_multiple_rustc_main, code = "E0137")]
+#[diag(passes_multiple_rustc_main, code = E0137)]
 pub struct MultipleRustcMain {
     #[primary_span]
     pub span: Span,
@@ -1240,7 +1240,7 @@ pub struct MultipleRustcMain {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_multiple_start_functions, code = "E0138")]
+#[diag(passes_multiple_start_functions, code = E0138)]
 pub struct MultipleStartFunctions {
     #[primary_span]
     pub span: Span,
@@ -1280,7 +1280,7 @@ impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for NoMainErr {
     fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> DiagnosticBuilder<'a, G> {
         let mut diag = DiagnosticBuilder::new(dcx, level, fluent::passes_no_main_function);
         diag.span(DUMMY_SP);
-        diag.code(error_code!(E0601));
+        diag.code(E0601);
         diag.arg("crate_name", self.crate_name);
         diag.arg("filename", self.filename);
         diag.arg("has_filename", self.has_filename);
@@ -1345,7 +1345,7 @@ fn into_diagnostic(self, dcx: &DiagCtxt, level: Level) -> DiagnosticBuilder<'_,
                 Duplicate::CrateDepends => fluent::passes_duplicate_lang_item_crate_depends,
             },
         );
-        diag.code(error_code!(E0152));
+        diag.code(E0152);
         diag.arg("lang_item_name", self.lang_item_name);
         diag.arg("crate_name", self.crate_name);
         diag.arg("dependency_of", self.dependency_of);
@@ -1382,7 +1382,7 @@ fn into_diagnostic(self, dcx: &DiagCtxt, level: Level) -> DiagnosticBuilder<'_,
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_incorrect_target, code = "E0718")]
+#[diag(passes_incorrect_target, code = E0718)]
 pub struct IncorrectTarget<'a> {
     #[primary_span]
     pub span: Span,
@@ -1418,7 +1418,7 @@ pub struct ObjectLifetimeErr {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_unrecognized_repr_hint, code = "E0552")]
+#[diag(passes_unrecognized_repr_hint, code = E0552)]
 #[help]
 pub struct UnrecognizedReprHint {
     #[primary_span]
@@ -1427,35 +1427,35 @@ pub struct UnrecognizedReprHint {
 
 #[derive(Diagnostic)]
 pub enum AttrApplication {
-    #[diag(passes_attr_application_enum, code = "E0517")]
+    #[diag(passes_attr_application_enum, code = E0517)]
     Enum {
         #[primary_span]
         hint_span: Span,
         #[label]
         span: Span,
     },
-    #[diag(passes_attr_application_struct, code = "E0517")]
+    #[diag(passes_attr_application_struct, code = E0517)]
     Struct {
         #[primary_span]
         hint_span: Span,
         #[label]
         span: Span,
     },
-    #[diag(passes_attr_application_struct_union, code = "E0517")]
+    #[diag(passes_attr_application_struct_union, code = E0517)]
     StructUnion {
         #[primary_span]
         hint_span: Span,
         #[label]
         span: Span,
     },
-    #[diag(passes_attr_application_struct_enum_union, code = "E0517")]
+    #[diag(passes_attr_application_struct_enum_union, code = E0517)]
     StructEnumUnion {
         #[primary_span]
         hint_span: Span,
         #[label]
         span: Span,
     },
-    #[diag(passes_attr_application_struct_enum_function_method_union, code = "E0517")]
+    #[diag(passes_attr_application_struct_enum_function_method_union, code = E0517)]
     StructEnumFunctionMethodUnion {
         #[primary_span]
         hint_span: Span,
@@ -1465,7 +1465,7 @@ pub enum AttrApplication {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_transparent_incompatible, code = "E0692")]
+#[diag(passes_transparent_incompatible, code = E0692)]
 pub struct TransparentIncompatible {
     #[primary_span]
     pub hint_spans: Vec<Span>,
@@ -1473,7 +1473,7 @@ pub struct TransparentIncompatible {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_deprecated_attribute, code = "E0549")]
+#[diag(passes_deprecated_attribute, code = E0549)]
 pub struct DeprecatedAttribute {
     #[primary_span]
     pub span: Span,
@@ -1524,7 +1524,7 @@ pub struct TraitImplConstStable {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_feature_only_on_nightly, code = "E0554")]
+#[diag(passes_feature_only_on_nightly, code = E0554)]
 pub struct FeatureOnlyOnNightly {
     #[primary_span]
     pub span: Span,
@@ -1532,7 +1532,7 @@ pub struct FeatureOnlyOnNightly {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_unknown_feature, code = "E0635")]
+#[diag(passes_unknown_feature, code = E0635)]
 pub struct UnknownFeature {
     #[primary_span]
     pub span: Span,
@@ -1549,7 +1549,7 @@ pub struct ImpliedFeatureNotExist {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_duplicate_feature_err, code = "E0636")]
+#[diag(passes_duplicate_feature_err, code = E0636)]
 pub struct DuplicateFeatureErr {
     #[primary_span]
     pub span: Span,
diff --git a/compiler/rustc_privacy/src/errors.rs b/compiler/rustc_privacy/src/errors.rs
index b1242f82f4f..01c6d18c0e1 100644
--- a/compiler/rustc_privacy/src/errors.rs
+++ b/compiler/rustc_privacy/src/errors.rs
@@ -1,9 +1,9 @@
-use rustc_errors::DiagnosticArgFromDisplay;
+use rustc_errors::{codes::*, DiagnosticArgFromDisplay};
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
 use rustc_span::{Span, Symbol};
 
 #[derive(Diagnostic)]
-#[diag(privacy_field_is_private, code = "E0451")]
+#[diag(privacy_field_is_private, code = E0451)]
 pub struct FieldIsPrivate {
     #[primary_span]
     pub span: Span,
@@ -48,7 +48,7 @@ pub struct UnnamedItemIsPrivate {
 }
 
 #[derive(Diagnostic)]
-#[diag(privacy_in_public_interface, code = "E0446")]
+#[diag(privacy_in_public_interface, code = E0446)]
 pub struct InPublicInterface<'a> {
     #[primary_span]
     #[label]
diff --git a/compiler/rustc_query_system/src/error.rs b/compiler/rustc_query_system/src/error.rs
index 5829e17ec16..9db6fac8036 100644
--- a/compiler/rustc_query_system/src/error.rs
+++ b/compiler/rustc_query_system/src/error.rs
@@ -1,3 +1,4 @@
+use rustc_errors::codes::*;
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_session::Limit;
 use rustc_span::{Span, Symbol};
@@ -45,7 +46,7 @@ pub struct CycleUsage {
 }
 
 #[derive(Diagnostic)]
-#[diag(query_system_cycle, code = "E0391")]
+#[diag(query_system_cycle, code = E0391)]
 pub struct Cycle {
     #[primary_span]
     pub span: Span,
diff --git a/compiler/rustc_resolve/src/build_reduced_graph.rs b/compiler/rustc_resolve/src/build_reduced_graph.rs
index b855ec8f920..7eb7c8c2bca 100644
--- a/compiler/rustc_resolve/src/build_reduced_graph.rs
+++ b/compiler/rustc_resolve/src/build_reduced_graph.rs
@@ -19,7 +19,7 @@
 use rustc_ast::{Block, ForeignItem, ForeignItemKind, Impl, Item, ItemKind, NodeId};
 use rustc_attr as attr;
 use rustc_data_structures::sync::Lrc;
-use rustc_errors::{struct_span_code_err, Applicability};
+use rustc_errors::{codes::*, struct_span_code_err, Applicability};
 use rustc_expand::expand::AstFragment;
 use rustc_hir::def::{self, *};
 use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_ID};
diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index 66dfee6c062..f3a6eb65a72 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -6,8 +6,8 @@
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{
-    pluralize, report_ambiguity_error, struct_span_code_err, Applicability, DiagCtxt, Diagnostic,
-    DiagnosticBuilder, ErrorGuaranteed, MultiSpan, SuggestionStyle,
+    codes::*, pluralize, report_ambiguity_error, struct_span_code_err, Applicability, DiagCtxt,
+    Diagnostic, DiagnosticBuilder, ErrorGuaranteed, MultiSpan, SuggestionStyle,
 };
 use rustc_feature::BUILTIN_ATTRIBUTES;
 use rustc_hir::def::Namespace::{self, *};
diff --git a/compiler/rustc_resolve/src/errors.rs b/compiler/rustc_resolve/src/errors.rs
index 5d9269d8f54..50ff09feb4d 100644
--- a/compiler/rustc_resolve/src/errors.rs
+++ b/compiler/rustc_resolve/src/errors.rs
@@ -1,3 +1,4 @@
+use rustc_errors::codes::*;
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::{
     symbol::{Ident, Symbol},
@@ -7,16 +8,16 @@
 use crate::{late::PatternSource, Res};
 
 #[derive(Diagnostic)]
-#[diag(resolve_parent_module_reset_for_binding, code = "E0637")]
+#[diag(resolve_parent_module_reset_for_binding, code = E0637)]
 pub(crate) struct ParentModuleResetForBinding;
 
 #[derive(Diagnostic)]
-#[diag(resolve_ampersand_used_without_explicit_lifetime_name, code = "E0637")]
+#[diag(resolve_ampersand_used_without_explicit_lifetime_name, code = E0637)]
 #[note]
 pub(crate) struct AmpersandUsedWithoutExplicitLifetimeName(#[primary_span] pub(crate) Span);
 
 #[derive(Diagnostic)]
-#[diag(resolve_underscore_lifetime_name_cannot_be_used_here, code = "E0637")]
+#[diag(resolve_underscore_lifetime_name_cannot_be_used_here, code = E0637)]
 #[note]
 pub(crate) struct UnderscoreLifetimeNameCannotBeUsedHere(#[primary_span] pub(crate) Span);
 
@@ -33,7 +34,7 @@
 pub(crate) struct ResolutionError(#[primary_span] pub(crate) Span);
 
 #[derive(Diagnostic)]
-#[diag(resolve_generic_params_from_outer_item, code = "E0401")]
+#[diag(resolve_generic_params_from_outer_item, code = E0401)]
 pub(crate) struct GenericParamsFromOuterItem {
     #[primary_span]
     #[label]
@@ -67,7 +68,7 @@ pub(crate) struct GenericParamsFromOuterItemSugg {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_name_is_already_used_as_generic_parameter, code = "E0403")]
+#[diag(resolve_name_is_already_used_as_generic_parameter, code = E0403)]
 pub(crate) struct NameAlreadyUsedInParameterList {
     #[primary_span]
     #[label]
@@ -78,7 +79,7 @@ pub(crate) struct NameAlreadyUsedInParameterList {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_method_not_member_of_trait, code = "E0407")]
+#[diag(resolve_method_not_member_of_trait, code = E0407)]
 pub(crate) struct MethodNotMemberOfTrait {
     #[primary_span]
     #[label]
@@ -102,7 +103,7 @@ pub(crate) struct AssociatedFnWithSimilarNameExists {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_type_not_member_of_trait, code = "E0437")]
+#[diag(resolve_type_not_member_of_trait, code = E0437)]
 pub(crate) struct TypeNotMemberOfTrait {
     #[primary_span]
     #[label]
@@ -126,7 +127,7 @@ pub(crate) struct AssociatedTypeWithSimilarNameExists {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_const_not_member_of_trait, code = "E0438")]
+#[diag(resolve_const_not_member_of_trait, code = E0438)]
 pub(crate) struct ConstNotMemberOfTrait {
     #[primary_span]
     #[label]
@@ -150,7 +151,7 @@ pub(crate) struct AssociatedConstWithSimilarNameExists {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_variable_bound_with_different_mode, code = "E0409")]
+#[diag(resolve_variable_bound_with_different_mode, code = E0409)]
 pub(crate) struct VariableBoundWithDifferentMode {
     #[primary_span]
     #[label]
@@ -161,7 +162,7 @@ pub(crate) struct VariableBoundWithDifferentMode {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_ident_bound_more_than_once_in_parameter_list, code = "E0415")]
+#[diag(resolve_ident_bound_more_than_once_in_parameter_list, code = E0415)]
 pub(crate) struct IdentifierBoundMoreThanOnceInParameterList {
     #[primary_span]
     #[label]
@@ -170,7 +171,7 @@ pub(crate) struct IdentifierBoundMoreThanOnceInParameterList {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_ident_bound_more_than_once_in_same_pattern, code = "E0416")]
+#[diag(resolve_ident_bound_more_than_once_in_same_pattern, code = E0416)]
 pub(crate) struct IdentifierBoundMoreThanOnceInSamePattern {
     #[primary_span]
     #[label]
@@ -179,7 +180,7 @@ pub(crate) struct IdentifierBoundMoreThanOnceInSamePattern {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_undeclared_label, code = "E0426")]
+#[diag(resolve_undeclared_label, code = E0426)]
 pub(crate) struct UndeclaredLabel {
     #[primary_span]
     #[label]
@@ -217,7 +218,7 @@ pub(crate) struct UnreachableLabelWithSimilarNameExists {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_self_import_can_only_appear_once_in_the_list, code = "E0430")]
+#[diag(resolve_self_import_can_only_appear_once_in_the_list, code = E0430)]
 pub(crate) struct SelfImportCanOnlyAppearOnceInTheList {
     #[primary_span]
     #[label]
@@ -225,7 +226,7 @@ pub(crate) struct SelfImportCanOnlyAppearOnceInTheList {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_self_import_only_in_import_list_with_non_empty_prefix, code = "E0431")]
+#[diag(resolve_self_import_only_in_import_list_with_non_empty_prefix, code = E0431)]
 pub(crate) struct SelfImportOnlyInImportListWithNonEmptyPrefix {
     #[primary_span]
     #[label]
@@ -233,7 +234,7 @@ pub(crate) struct SelfImportOnlyInImportListWithNonEmptyPrefix {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_cannot_capture_dynamic_environment_in_fn_item, code = "E0434")]
+#[diag(resolve_cannot_capture_dynamic_environment_in_fn_item, code = E0434)]
 #[help]
 pub(crate) struct CannotCaptureDynamicEnvironmentInFnItem {
     #[primary_span]
@@ -241,7 +242,7 @@ pub(crate) struct CannotCaptureDynamicEnvironmentInFnItem {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_attempt_to_use_non_constant_value_in_constant, code = "E0435")]
+#[diag(resolve_attempt_to_use_non_constant_value_in_constant, code = E0435)]
 pub(crate) struct AttemptToUseNonConstantValueInConstant<'a> {
     #[primary_span]
     pub(crate) span: Span,
@@ -283,7 +284,7 @@ pub(crate) struct AttemptToUseNonConstantValueInConstantWithoutSuggestion<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_self_imports_only_allowed_within, code = "E0429")]
+#[diag(resolve_self_imports_only_allowed_within, code = E0429)]
 pub(crate) struct SelfImportsOnlyAllowedWithin {
     #[primary_span]
     pub(crate) span: Span,
@@ -317,7 +318,7 @@ pub(crate) struct SelfImportsOnlyAllowedWithinMultipartSuggestion {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_binding_shadows_something_unacceptable, code = "E0530")]
+#[diag(resolve_binding_shadows_something_unacceptable, code = E0530)]
 pub(crate) struct BindingShadowsSomethingUnacceptable<'a> {
     #[primary_span]
     #[label]
@@ -346,7 +347,7 @@ pub(crate) struct BindingShadowsSomethingUnacceptableSuggestion {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_forward_declared_generic_param, code = "E0128")]
+#[diag(resolve_forward_declared_generic_param, code = E0128)]
 pub(crate) struct ForwardDeclaredGenericParam {
     #[primary_span]
     #[label]
@@ -354,7 +355,7 @@ pub(crate) struct ForwardDeclaredGenericParam {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_param_in_ty_of_const_param, code = "E0770")]
+#[diag(resolve_param_in_ty_of_const_param, code = E0770)]
 pub(crate) struct ParamInTyOfConstParam {
     #[primary_span]
     #[label]
@@ -376,7 +377,7 @@ pub(crate) enum ParamKindInTyOfConstParam {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_self_in_generic_param_default, code = "E0735")]
+#[diag(resolve_self_in_generic_param_default, code = E0735)]
 pub(crate) struct SelfInGenericParamDefault {
     #[primary_span]
     #[label]
@@ -412,7 +413,7 @@ pub(crate) enum ParamKindInNonTrivialAnonConst {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_unreachable_label, code = "E0767")]
+#[diag(resolve_unreachable_label, code = E0767)]
 #[note]
 pub(crate) struct UnreachableLabel {
     #[primary_span]
@@ -495,7 +496,7 @@ pub(crate) struct BindingInNeverPattern {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_trait_impl_duplicate, code = "E0201")]
+#[diag(resolve_trait_impl_duplicate, code = E0201)]
 pub(crate) struct TraitImplDuplicate {
     #[primary_span]
     #[label]
@@ -518,11 +519,11 @@ pub(crate) struct Relative2018 {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_ancestor_only, code = "E0742")]
+#[diag(resolve_ancestor_only, code = E0742)]
 pub(crate) struct AncestorOnly(#[primary_span] pub(crate) Span);
 
 #[derive(Diagnostic)]
-#[diag(resolve_expected_found, code = "E0577")]
+#[diag(resolve_expected_found, code = E0577)]
 pub(crate) struct ExpectedFound {
     #[primary_span]
     #[label]
@@ -532,7 +533,7 @@ pub(crate) struct ExpectedFound {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_indeterminate, code = "E0578")]
+#[diag(resolve_indeterminate, code = E0578)]
 pub(crate) struct Indeterminate(#[primary_span] pub(crate) Span);
 
 #[derive(Diagnostic)]
@@ -714,7 +715,7 @@ pub(crate) struct CannotDetermineMacroResolution {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_cannot_be_reexported_private, code = "E0364")]
+#[diag(resolve_cannot_be_reexported_private, code = E0364)]
 pub(crate) struct CannotBeReexportedPrivate {
     #[primary_span]
     pub(crate) span: Span,
@@ -722,7 +723,7 @@ pub(crate) struct CannotBeReexportedPrivate {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_cannot_be_reexported_crate_public, code = "E0364")]
+#[diag(resolve_cannot_be_reexported_crate_public, code = E0364)]
 pub(crate) struct CannotBeReexportedCratePublic {
     #[primary_span]
     pub(crate) span: Span,
@@ -730,7 +731,7 @@ pub(crate) struct CannotBeReexportedCratePublic {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_cannot_be_reexported_private, code = "E0365")]
+#[diag(resolve_cannot_be_reexported_private, code = E0365)]
 #[note(resolve_consider_declaring_with_pub)]
 pub(crate) struct CannotBeReexportedPrivateNS {
     #[primary_span]
@@ -740,7 +741,7 @@ pub(crate) struct CannotBeReexportedPrivateNS {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_cannot_be_reexported_crate_public, code = "E0365")]
+#[diag(resolve_cannot_be_reexported_crate_public, code = E0365)]
 #[note(resolve_consider_declaring_with_pub)]
 pub(crate) struct CannotBeReexportedCratePublicNS {
     #[primary_span]
@@ -779,7 +780,7 @@ pub(crate) struct ItemsInTraitsAreNotImportable {
 }
 
 #[derive(Diagnostic)]
-#[diag(resolve_is_not_directly_importable, code = "E0253")]
+#[diag(resolve_is_not_directly_importable, code = E0253)]
 pub(crate) struct IsNotDirectlyImportable {
     #[primary_span]
     #[label]
diff --git a/compiler/rustc_resolve/src/imports.rs b/compiler/rustc_resolve/src/imports.rs
index ad60caed354..30fb35238c3 100644
--- a/compiler/rustc_resolve/src/imports.rs
+++ b/compiler/rustc_resolve/src/imports.rs
@@ -17,7 +17,7 @@
 use rustc_ast::NodeId;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::intern::Interned;
-use rustc_errors::{pluralize, struct_span_code_err, Applicability, MultiSpan};
+use rustc_errors::{codes::*, pluralize, struct_span_code_err, Applicability, MultiSpan};
 use rustc_hir::def::{self, DefKind, PartialRes};
 use rustc_middle::metadata::ModChild;
 use rustc_middle::metadata::Reexport;
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index 18926463d6b..0743ff03864 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -16,7 +16,9 @@
 use rustc_ast::visit::{self, AssocCtxt, BoundKind, FnCtxt, FnKind, Visitor};
 use rustc_ast::*;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
-use rustc_errors::{Applicability, DiagnosticArgValue, IntoDiagnosticArg};
+use rustc_errors::{
+    codes::*, struct_span_code_err, Applicability, DiagnosticArgValue, ErrCode, IntoDiagnosticArg,
+};
 use rustc_hir::def::Namespace::{self, *};
 use rustc_hir::def::{self, CtorKind, DefKind, LifetimeRes, NonMacroAttrKind, PartialRes, PerNS};
 use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_ID, LOCAL_CRATE};
@@ -533,21 +535,20 @@ pub(crate) fn is_expected(self, res: Res) -> bool {
         }
     }
 
-    fn error_code(self, has_unexpected_resolution: bool) -> String {
-        use rustc_errors::error_code;
+    fn error_code(self, has_unexpected_resolution: bool) -> ErrCode {
         match (self, has_unexpected_resolution) {
-            (PathSource::Trait(_), true) => error_code!(E0404),
-            (PathSource::Trait(_), false) => error_code!(E0405),
-            (PathSource::Type, true) => error_code!(E0573),
-            (PathSource::Type, false) => error_code!(E0412),
-            (PathSource::Struct, true) => error_code!(E0574),
-            (PathSource::Struct, false) => error_code!(E0422),
-            (PathSource::Expr(..), true) | (PathSource::Delegation, true) => error_code!(E0423),
-            (PathSource::Expr(..), false) | (PathSource::Delegation, false) => error_code!(E0425),
-            (PathSource::Pat | PathSource::TupleStruct(..), true) => error_code!(E0532),
-            (PathSource::Pat | PathSource::TupleStruct(..), false) => error_code!(E0531),
-            (PathSource::TraitItem(..), true) => error_code!(E0575),
-            (PathSource::TraitItem(..), false) => error_code!(E0576),
+            (PathSource::Trait(_), true) => E0404,
+            (PathSource::Trait(_), false) => E0405,
+            (PathSource::Type, true) => E0573,
+            (PathSource::Type, false) => E0412,
+            (PathSource::Struct, true) => E0574,
+            (PathSource::Struct, false) => E0422,
+            (PathSource::Expr(..), true) | (PathSource::Delegation, true) => E0423,
+            (PathSource::Expr(..), false) | (PathSource::Delegation, false) => E0425,
+            (PathSource::Pat | PathSource::TupleStruct(..), true) => E0532,
+            (PathSource::Pat | PathSource::TupleStruct(..), false) => E0531,
+            (PathSource::TraitItem(..), true) => E0575,
+            (PathSource::TraitItem(..), false) => E0576,
         }
     }
 }
@@ -1673,13 +1674,8 @@ fn resolve_anonymous_lifetime(&mut self, lifetime: &Lifetime, elided: bool) {
                     } else {
                         ("`'_` cannot be used here", "`'_` is a reserved lifetime name")
                     };
-                    let mut diag = rustc_errors::struct_span_code_err!(
-                        self.r.dcx(),
-                        lifetime.ident.span,
-                        E0637,
-                        "{}",
-                        msg,
-                    );
+                    let mut diag =
+                        struct_span_code_err!(self.r.dcx(), lifetime.ident.span, E0637, "{}", msg,);
                     diag.span_label(lifetime.ident.span, note);
                     if elided {
                         for rib in self.lifetime_ribs[i..].iter().rev() {
@@ -1863,7 +1859,7 @@ fn resolve_elided_lifetimes_in_path(
                     LifetimeRibKind::AnonymousCreateParameter { report_in_path: true, .. }
                     | LifetimeRibKind::AnonymousWarn(_) => {
                         let sess = self.r.tcx.sess;
-                        let mut err = rustc_errors::struct_span_code_err!(
+                        let mut err = struct_span_code_err!(
                             sess.dcx(),
                             path_span,
                             E0726,
@@ -2608,7 +2604,7 @@ fn with_generic_param_rib<'c, F>(
             }
 
             if param.ident.name == kw::UnderscoreLifetime {
-                rustc_errors::struct_span_code_err!(
+                struct_span_code_err!(
                     self.r.dcx(),
                     param.ident.span,
                     E0637,
@@ -2622,7 +2618,7 @@ fn with_generic_param_rib<'c, F>(
             }
 
             if param.ident.name == kw::StaticLifetime {
-                rustc_errors::struct_span_code_err!(
+                struct_span_code_err!(
                     self.r.dcx(),
                     param.ident.span,
                     E0262,
@@ -3164,10 +3160,10 @@ fn check_trait_item<F>(
         // The method kind does not correspond to what appeared in the trait, report.
         let path = &self.current_trait_ref.as_ref().unwrap().1.path;
         let (code, kind) = match kind {
-            AssocItemKind::Const(..) => (rustc_errors::error_code!(E0323), "const"),
-            AssocItemKind::Fn(..) => (rustc_errors::error_code!(E0324), "method"),
-            AssocItemKind::Type(..) => (rustc_errors::error_code!(E0325), "type"),
-            AssocItemKind::Delegation(..) => (rustc_errors::error_code!(E0324), "method"),
+            AssocItemKind::Const(..) => (E0323, "const"),
+            AssocItemKind::Fn(..) => (E0324, "method"),
+            AssocItemKind::Type(..) => (E0325, "type"),
+            AssocItemKind::Delegation(..) => (E0324, "method"),
             AssocItemKind::MacCall(..) => span_bug!(span, "unexpanded macro"),
         };
         let trait_path = path_names_to_string(path);
diff --git a/compiler/rustc_resolve/src/late/diagnostics.rs b/compiler/rustc_resolve/src/late/diagnostics.rs
index abb0a7a465a..a4c041f1ff2 100644
--- a/compiler/rustc_resolve/src/late/diagnostics.rs
+++ b/compiler/rustc_resolve/src/late/diagnostics.rs
@@ -16,8 +16,8 @@
 use rustc_ast_pretty::pprust::where_bound_predicate_to_string;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{
-    pluralize, struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
-    MultiSpan, SuggestionStyle,
+    codes::*, pluralize, struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder,
+    ErrorGuaranteed, MultiSpan, SuggestionStyle,
 };
 use rustc_hir as hir;
 use rustc_hir::def::{self, CtorKind, CtorOf, DefKind};
@@ -922,8 +922,8 @@ fn err_code_special_cases(
         path: &[Segment],
         span: Span,
     ) {
-        if let Some(err_code) = &err.code {
-            if err_code == &rustc_errors::error_code!(E0425) {
+        if let Some(err_code) = err.code {
+            if err_code == E0425 {
                 for label_rib in &self.label_ribs {
                     for (label_ident, node_id) in &label_rib.bindings {
                         let ident = path.last().unwrap().ident;
@@ -946,7 +946,7 @@ fn err_code_special_cases(
                         }
                     }
                 }
-            } else if err_code == &rustc_errors::error_code!(E0412) {
+            } else if err_code == E0412 {
                 if let Some(correct) = Self::likely_rust_type(path) {
                     err.span_suggestion(
                         span,
@@ -970,7 +970,7 @@ fn suggest_self_ty(
         if !is_self_type(path, source.namespace()) {
             return false;
         }
-        err.code(rustc_errors::error_code!(E0411));
+        err.code(E0411);
         err.span_label(span, "`Self` is only available in impls, traits, and type definitions");
         if let Some(item_kind) = self.diagnostic_metadata.current_item {
             if !item_kind.ident.span.is_dummy() {
@@ -999,7 +999,7 @@ fn suggest_self_value(
         }
 
         debug!("smart_resolve_path_fragment: E0424, source={:?}", source);
-        err.code(rustc_errors::error_code!(E0424));
+        err.code(E0424);
         err.span_label(
             span,
             match source {
diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index 925c3c0e27d..9d09d060b59 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -35,7 +35,7 @@
 use rustc_data_structures::intern::Interned;
 use rustc_data_structures::steal::Steal;
 use rustc_data_structures::sync::{FreezeReadGuard, Lrc};
-use rustc_errors::{Applicability, DiagnosticBuilder};
+use rustc_errors::{Applicability, DiagnosticBuilder, ErrCode};
 use rustc_expand::base::{DeriveResolutions, SyntaxExtension, SyntaxExtensionKind};
 use rustc_feature::BUILTIN_ATTRIBUTES;
 use rustc_hir::def::Namespace::{self, *};
@@ -256,7 +256,7 @@ enum ResolutionError<'a> {
         kind: &'static str,
         trait_path: String,
         trait_item_span: Span,
-        code: String,
+        code: ErrCode,
     },
     /// Error E0201: multiple impl items for the same trait item.
     TraitImplDuplicate { name: Symbol, trait_item_span: Span, old_span: Span },
diff --git a/compiler/rustc_resolve/src/macros.rs b/compiler/rustc_resolve/src/macros.rs
index 1c085ddf57b..a6bf289a76a 100644
--- a/compiler/rustc_resolve/src/macros.rs
+++ b/compiler/rustc_resolve/src/macros.rs
@@ -15,7 +15,7 @@
 use rustc_attr::StabilityLevel;
 use rustc_data_structures::intern::Interned;
 use rustc_data_structures::sync::Lrc;
-use rustc_errors::{struct_span_code_err, Applicability};
+use rustc_errors::{codes::*, struct_span_code_err, Applicability};
 use rustc_expand::base::{Annotatable, DeriveResolutions, Indeterminate, ResolverExpand};
 use rustc_expand::base::{SyntaxExtension, SyntaxExtensionKind};
 use rustc_expand::compile_declarative_macro;
diff --git a/compiler/rustc_session/src/errors.rs b/compiler/rustc_session/src/errors.rs
index e19f0fd84de..c36cec6f353 100644
--- a/compiler/rustc_session/src/errors.rs
+++ b/compiler/rustc_session/src/errors.rs
@@ -3,7 +3,7 @@
 use rustc_ast::token;
 use rustc_ast::util::literal::LitError;
 use rustc_errors::{
-    error_code, DiagCtxt, DiagnosticBuilder, DiagnosticMessage, IntoDiagnostic, Level, MultiSpan,
+    codes::*, DiagCtxt, DiagnosticBuilder, DiagnosticMessage, IntoDiagnostic, Level, MultiSpan,
 };
 use rustc_macros::Diagnostic;
 use rustc_span::{Span, Symbol};
@@ -19,9 +19,7 @@ pub struct FeatureGateError {
 impl<'a> IntoDiagnostic<'a> for FeatureGateError {
     #[track_caller]
     fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> DiagnosticBuilder<'a> {
-        DiagnosticBuilder::new(dcx, level, self.explain)
-            .with_span(self.span)
-            .with_code(error_code!(E0658))
+        DiagnosticBuilder::new(dcx, level, self.explain).with_span(self.span).with_code(E0658)
     }
 }
 
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 891a83ce80c..7cd76ad7293 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -22,7 +22,7 @@
 use rustc_errors::json::JsonEmitter;
 use rustc_errors::registry::Registry;
 use rustc_errors::{
-    error_code, fallback_fluent_bundle, DiagCtxt, DiagnosticBuilder, DiagnosticMessage,
+    codes::*, fallback_fluent_bundle, DiagCtxt, DiagnosticBuilder, DiagnosticMessage, ErrCode,
     ErrorGuaranteed, FatalAbort, FluentBundle, IntoDiagnostic, LazyFallbackBundle, TerminalUrl,
 };
 use rustc_macros::HashStable_Generic;
@@ -316,7 +316,7 @@ pub fn create_feature_err<'a>(
     ) -> DiagnosticBuilder<'a> {
         let mut err = self.dcx().create_err(err);
         if err.code.is_none() {
-            err.code(error_code!(E0658));
+            err.code(E0658);
         }
         add_feature_diagnostics(&mut err, self, feature);
         err
@@ -893,7 +893,7 @@ pub fn codegen_units(&self) -> CodegenUnits {
         CodegenUnits::Default(16)
     }
 
-    pub fn teach(&self, code: &str) -> bool {
+    pub fn teach(&self, code: ErrCode) -> bool {
         self.opts.unstable_opts.teach && self.dcx().must_teach(code)
     }
 
diff --git a/compiler/rustc_trait_selection/src/errors.rs b/compiler/rustc_trait_selection/src/errors.rs
index 5eff52afbca..7894f8dd98f 100644
--- a/compiler/rustc_trait_selection/src/errors.rs
+++ b/compiler/rustc_trait_selection/src/errors.rs
@@ -1,7 +1,7 @@
 use crate::fluent_generated as fluent;
 use rustc_errors::{
-    AddToDiagnostic, Applicability, DiagCtxt, Diagnostic, DiagnosticBuilder, EmissionGuarantee,
-    IntoDiagnostic, Level, SubdiagnosticMessage,
+    codes::*, AddToDiagnostic, Applicability, DiagCtxt, Diagnostic, DiagnosticBuilder,
+    EmissionGuarantee, IntoDiagnostic, Level, SubdiagnosticMessage,
 };
 use rustc_macros::Diagnostic;
 use rustc_middle::ty::{self, ClosureKind, PolyTraitRef, Ty};
@@ -25,7 +25,7 @@ pub struct UnableToConstructConstantValue<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(trait_selection_empty_on_clause_in_rustc_on_unimplemented, code = "E0232")]
+#[diag(trait_selection_empty_on_clause_in_rustc_on_unimplemented, code = E0232)]
 pub struct EmptyOnClauseInOnUnimplemented {
     #[primary_span]
     #[label]
@@ -33,7 +33,7 @@ pub struct EmptyOnClauseInOnUnimplemented {
 }
 
 #[derive(Diagnostic)]
-#[diag(trait_selection_invalid_on_clause_in_rustc_on_unimplemented, code = "E0232")]
+#[diag(trait_selection_invalid_on_clause_in_rustc_on_unimplemented, code = E0232)]
 pub struct InvalidOnClauseInOnUnimplemented {
     #[primary_span]
     #[label]
@@ -41,7 +41,7 @@ pub struct InvalidOnClauseInOnUnimplemented {
 }
 
 #[derive(Diagnostic)]
-#[diag(trait_selection_no_value_in_rustc_on_unimplemented, code = "E0232")]
+#[diag(trait_selection_no_value_in_rustc_on_unimplemented, code = E0232)]
 #[note]
 pub struct NoValueInOnUnimplemented {
     #[primary_span]
@@ -59,17 +59,13 @@ pub struct NegativePositiveConflict<'tcx> {
 
 impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for NegativePositiveConflict<'_> {
     #[track_caller]
-    fn into_diagnostic(
-        self,
-        dcx: &DiagCtxt,
-        level: Level,
-    ) -> rustc_errors::DiagnosticBuilder<'_, G> {
+    fn into_diagnostic(self, dcx: &DiagCtxt, level: Level) -> DiagnosticBuilder<'_, G> {
         let mut diag =
             DiagnosticBuilder::new(dcx, level, fluent::trait_selection_negative_positive_conflict);
         diag.arg("trait_desc", self.trait_desc.print_only_trait_path().to_string());
         diag.arg("self_desc", self.self_ty.map_or_else(|| "none".to_string(), |ty| ty.to_string()));
         diag.span(self.impl_span);
-        diag.code(rustc_errors::error_code!(E0751));
+        diag.code(E0751);
         match self.negative_impl_span {
             Ok(span) => {
                 diag.span_label(span, fluent::trait_selection_negative_implementation_here);
@@ -132,7 +128,7 @@ fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
 }
 
 #[derive(Diagnostic)]
-#[diag(trait_selection_closure_kind_mismatch, code = "E0525")]
+#[diag(trait_selection_closure_kind_mismatch, code = E0525)]
 pub struct ClosureKindMismatch {
     #[primary_span]
     #[label]
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/infer_ctxt_ext.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/infer_ctxt_ext.rs
index 864580afe62..ca43436848b 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/infer_ctxt_ext.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/infer_ctxt_ext.rs
@@ -1,7 +1,7 @@
 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use crate::infer::InferCtxt;
 use crate::traits::{Obligation, ObligationCause, ObligationCtxt};
-use rustc_errors::{pluralize, struct_span_code_err, Applicability, DiagnosticBuilder};
+use rustc_errors::{codes::*, pluralize, struct_span_code_err, Applicability, DiagnosticBuilder};
 use rustc_hir as hir;
 use rustc_hir::Node;
 use rustc_middle::ty::{self, Ty};
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
index bb1b6ec1390..972da180a33 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
@@ -6,7 +6,7 @@
 use rustc_ast::{Attribute, MetaItem, NestedMetaItem};
 use rustc_attr as attr;
 use rustc_data_structures::fx::FxHashMap;
-use rustc_errors::{struct_span_code_err, ErrorGuaranteed};
+use rustc_errors::{codes::*, struct_span_code_err, ErrorGuaranteed};
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::ty::GenericArgsRef;
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 6a40ffebdad..cdf99870006 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -13,7 +13,7 @@
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_errors::{
-    error_code, pluralize, struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder,
+    codes::*, pluralize, struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder,
     MultiSpan, Style, SuggestionStyle,
 };
 use rustc_hir as hir;
@@ -2014,7 +2014,7 @@ fn suggest_impl_trait(
             return false;
         };
 
-        err.code(error_code!(E0746));
+        err.code(E0746);
         err.primary_message("return type cannot have an unboxed trait object");
         err.children.clear();
 
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs
index 149dcffe333..2a09e95b2c5 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs
@@ -19,8 +19,8 @@
 };
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
 use rustc_errors::{
-    pluralize, struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
-    MultiSpan, StashKey, Style,
+    codes::*, pluralize, struct_span_code_err, Applicability, Diagnostic, DiagnosticBuilder,
+    ErrorGuaranteed, MultiSpan, StashKey, Style,
 };
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Namespace, Res};
@@ -2529,7 +2529,7 @@ fn maybe_report_ambiguity(&self, obligation: &PredicateObligation<'tcx>) {
                                  corresponding `impl` type",
                             ),
                         );
-                        err.code(rustc_errors::error_code!(E0790));
+                        err.code(E0790);
 
                         if let Some(local_def_id) = data.trait_ref.def_id.as_local()
                             && let Some(hir::Node::Item(hir::Item {
@@ -3162,7 +3162,7 @@ fn add_tuple_trait_message(
             | ObligationCauseCode::ItemObligation(def_id)
                 if self.tcx.is_fn_trait(*def_id) =>
             {
-                err.code(rustc_errors::error_code!(E0059));
+                err.code(E0059);
                 err.primary_message(format!(
                     "type parameter to bare `{}` trait must be a tuple",
                     self.tcx.def_path_str(*def_id)
diff --git a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
index bfc6937a3eb..de08e7d2f03 100644
--- a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
@@ -20,7 +20,7 @@
     self, coherence, FutureCompatOverlapErrorKind, ObligationCause, ObligationCtxt,
 };
 use rustc_data_structures::fx::FxIndexSet;
-use rustc_errors::{error_code, DelayDm, Diagnostic};
+use rustc_errors::{codes::*, DelayDm, Diagnostic};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::ty::{self, ImplSubject, Ty, TyCtxt, TypeVisitableExt};
 use rustc_middle::ty::{GenericArgs, GenericArgsRef};
@@ -449,7 +449,7 @@ fn decorate<'tcx>(
                 || tcx.orphan_check_impl(impl_def_id).is_ok()
             {
                 let mut err = tcx.dcx().struct_span_err(impl_span, msg);
-                err.code(error_code!(E0119));
+                err.code(E0119);
                 decorate(tcx, &overlap, impl_span, &mut err);
                 err.emit()
             } else {
diff --git a/compiler/rustc_ty_utils/src/errors.rs b/compiler/rustc_ty_utils/src/errors.rs
index 947d4bbe86e..bfbb45f0cb5 100644
--- a/compiler/rustc_ty_utils/src/errors.rs
+++ b/compiler/rustc_ty_utils/src/errors.rs
@@ -1,5 +1,6 @@
 //! Errors emitted by ty_utils
 
+use rustc_errors::codes::*;
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_middle::ty::{GenericArg, Ty};
 use rustc_span::Span;
@@ -113,7 +114,7 @@ pub struct DuplicateArg<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(ty_utils_impl_trait_not_param, code = "E0792")]
+#[diag(ty_utils_impl_trait_not_param, code = E0792)]
 pub struct NotParam<'tcx> {
     pub arg: GenericArg<'tcx>,
     #[primary_span]
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 8706abda979..e1829da6e2c 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -15,6 +15,7 @@
 use rustc_ast::tokenstream::{TokenStream, TokenTree};
 use rustc_attr as attr;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap, FxIndexSet, IndexEntry};
+use rustc_errors::{codes::*, struct_span_code_err, FatalError};
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, DefKind, Res};
 use rustc_hir::def_id::{DefId, DefIdMap, DefIdSet, LocalDefId, LOCAL_CRATE};
@@ -2271,7 +2272,7 @@ pub(crate) fn clean_middle_ty<'tcx>(
         ty::Placeholder(..) => panic!("Placeholder"),
         ty::CoroutineWitness(..) => panic!("CoroutineWitness"),
         ty::Infer(..) => panic!("Infer"),
-        ty::Error(_) => rustc_errors::FatalError.raise(),
+        ty::Error(_) => FatalError.raise(),
     }
 }
 
@@ -2995,7 +2996,7 @@ fn clean_use_statement_inner<'tcx>(
         visibility.is_accessible_from(parent_mod, cx.tcx) && !current_mod.is_top_level_module();
 
     if pub_underscore && let Some(ref inline) = inline_attr {
-        rustc_errors::struct_span_code_err!(
+        struct_span_code_err!(
             cx.tcx.dcx(),
             inline.span(),
             E0780,
diff --git a/src/librustdoc/core.rs b/src/librustdoc/core.rs
index 7cf385de6b7..9eb62c25892 100644
--- a/src/librustdoc/core.rs
+++ b/src/librustdoc/core.rs
@@ -3,7 +3,7 @@
 use rustc_data_structures::unord::UnordSet;
 use rustc_errors::emitter::{DynEmitter, HumanEmitter};
 use rustc_errors::json::JsonEmitter;
-use rustc_errors::TerminalUrl;
+use rustc_errors::{codes::*, TerminalUrl};
 use rustc_feature::UnstableFeatures;
 use rustc_hir::def::Res;
 use rustc_hir::def_id::{DefId, DefIdMap, DefIdSet, LocalDefId};
diff --git a/src/tools/error_index_generator/Cargo.toml b/src/tools/error_index_generator/Cargo.toml
index 76c2e330b21..f4dac6e947e 100644
--- a/src/tools/error_index_generator/Cargo.toml
+++ b/src/tools/error_index_generator/Cargo.toml
@@ -5,7 +5,6 @@ edition = "2021"
 
 [dependencies]
 mdbook = { version = "0.4", default-features = false, features = ["search"] }
-rustc_error_codes = { version = "0.0.0", path = "../../../compiler/rustc_error_codes" }
 
 [[bin]]
 name = "error_index_generator"
diff --git a/src/tools/error_index_generator/main.rs b/src/tools/error_index_generator/main.rs
index 865d7172cd3..2de2d959a95 100644
--- a/src/tools/error_index_generator/main.rs
+++ b/src/tools/error_index_generator/main.rs
@@ -4,13 +4,15 @@
 extern crate rustc_log;
 extern crate rustc_session;
 
+extern crate rustc_errors;
+use rustc_errors::codes::DIAGNOSTICS;
+
 use std::env;
 use std::error::Error;
 use std::fs::{self, File};
 use std::io::Write;
 use std::path::Path;
 use std::path::PathBuf;
-
 use std::str::FromStr;
 
 use mdbook::book::{parse_summary, BookItem, Chapter};
@@ -38,7 +40,7 @@ fn render_markdown(output_path: &Path) -> Result<(), Box<dyn Error>> {
 
     write!(output_file, "# Rust Compiler Error Index\n")?;
 
-    for (err_code, description) in rustc_error_codes::DIAGNOSTICS.iter() {
+    for (err_code, description) in DIAGNOSTICS.iter() {
         write!(output_file, "## {}\n{}\n", err_code, description)?
     }
 
@@ -85,7 +87,7 @@ fn render_html(output_path: &Path) -> Result<(), Box<dyn Error>> {
 "
     );
 
-    let err_codes = rustc_error_codes::DIAGNOSTICS;
+    let err_codes = DIAGNOSTICS;
     let mut chapters = Vec::with_capacity(err_codes.len());
 
     for (err_code, explanation) in err_codes.iter() {
diff --git a/src/tools/tidy/src/error_codes.rs b/src/tools/tidy/src/error_codes.rs
index 094efa981d3..6fc65e56901 100644
--- a/src/tools/tidy/src/error_codes.rs
+++ b/src/tools/tidy/src/error_codes.rs
@@ -2,7 +2,7 @@
 //!
 //! Overview of check:
 //!
-//! 1. We create a list of error codes used by the compiler. Error codes are extracted from `compiler/rustc_error_codes/src/error_codes.rs`.
+//! 1. We create a list of error codes used by the compiler. Error codes are extracted from `compiler/rustc_error_codes/src/lib.rs`.
 //!
 //! 2. We check that the error code has a long-form explanation in `compiler/rustc_error_codes/src/error_codes/`.
 //!   - The explanation is expected to contain a `doctest` that fails with the correct error code. (`EXEMPT_FROM_DOCTEST` *currently* bypasses this check)
@@ -22,7 +22,7 @@
 
 use crate::walk::{filter_dirs, walk, walk_many};
 
-const ERROR_CODES_PATH: &str = "compiler/rustc_error_codes/src/error_codes.rs";
+const ERROR_CODES_PATH: &str = "compiler/rustc_error_codes/src/lib.rs";
 const ERROR_DOCS_PATH: &str = "compiler/rustc_error_codes/src/error_codes/";
 const ERROR_TESTS_PATH: &str = "tests/ui/error-codes/";
 
@@ -80,13 +80,14 @@ fn extract_error_codes(root_path: &Path, errors: &mut Vec<String>) -> Vec<String
         if line.starts_with('E') {
             let split_line = line.split_once(':');
 
-            // Extract the error code from the line, emitting a fatal error if it is not in a correct format.
+            // Extract the error code from the line. Emit a fatal error if it is not in the correct
+            // format.
             let err_code = if let Some(err_code) = split_line {
                 err_code.0.to_owned()
             } else {
                 errors.push(format!(
-                    "Expected a line with the format `Exxxx: include_str!(\"..\")`, but got \"{}\" \
-                    without a `:` delimiter",
+                    "Expected a line with the format `Eabcd: abcd, \
+                    but got \"{}\" without a `:` delimiter",
                     line,
                 ));
                 continue;
@@ -98,12 +99,16 @@ fn extract_error_codes(root_path: &Path, errors: &mut Vec<String>) -> Vec<String
                 continue;
             }
 
+            let mut chars = err_code.chars();
+            chars.next();
+            let error_num_as_str = chars.as_str();
+
             // Ensure that the line references the correct markdown file.
-            let expected_filename = format!(" include_str!(\"./error_codes/{}.md\"),", err_code);
+            let expected_filename = format!(" {},", error_num_as_str);
             if expected_filename != split_line.unwrap().1 {
                 errors.push(format!(
-                    "Error code `{}` expected to reference docs with `{}` but instead found `{}` in \
-                    `compiler/rustc_error_codes/src/error_codes.rs`",
+                    "`{}:` should be followed by `{}` but instead found `{}` in \
+                    `compiler/rustc_error_codes/src/lib.rs`",
                     err_code,
                     expected_filename,
                     split_line.unwrap().1,
@@ -311,13 +316,8 @@ fn check_error_codes_used(
     no_longer_emitted: &[String],
     verbose: bool,
 ) {
-    // We want error codes which match the following cases:
-    //
-    // * foo(a, E0111, a)
-    // * foo(a, E0111)
-    // * foo(E0111, a)
-    // * #[error = "E0111"]
-    let regex = Regex::new(r#"[(,"\s](E\d{4})[,)"]"#).unwrap();
+    // Search for error codes in the form `E0123`.
+    let regex = Regex::new(r#"\bE\d{4}\b"#).unwrap();
 
     let mut found_codes = Vec::new();
 
@@ -336,12 +336,12 @@ fn check_error_codes_used(
             }
 
             for cap in regex.captures_iter(line) {
-                if let Some(error_code) = cap.get(1) {
+                if let Some(error_code) = cap.get(0) {
                     let error_code = error_code.as_str().to_owned();
 
                     if !error_codes.contains(&error_code) {
                         // This error code isn't properly defined, we must error.
-                        errors.push(format!("Error code `{}` is used in the compiler but not defined and documented in `compiler/rustc_error_codes/src/error_codes.rs`.", error_code));
+                        errors.push(format!("Error code `{}` is used in the compiler but not defined and documented in `compiler/rustc_error_codes/src/lib.rs`.", error_code));
                         continue;
                     }
 
diff --git a/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.rs b/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.rs
index f553aa96505..d3cfd28082d 100644
--- a/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.rs
+++ b/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.rs
@@ -25,22 +25,26 @@
 use rustc_middle::ty::Ty;
 
 extern crate rustc_errors;
-use rustc_errors::{Applicability, DiagnosticMessage, MultiSpan, SubdiagnosticMessage};
+use rustc_errors::{Applicability, DiagnosticMessage, ErrCode, MultiSpan, SubdiagnosticMessage};
 
 extern crate rustc_session;
 
 rustc_fluent_macro::fluent_messages! { "./example.ftl" }
 
+// E0123 and E0456 are no longer used, so we define our own constants here just for this test.
+const E0123: ErrCode = ErrCode::from_u32(0123);
+const E0456: ErrCode = ErrCode::from_u32(0456);
+
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct Hello {}
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct HelloWarn {}
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 //~^ ERROR unsupported type attribute for diagnostic derive enum
 enum DiagnosticOnEnum {
     Foo,
@@ -50,53 +54,53 @@ enum DiagnosticOnEnum {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 #[diag = "E0123"]
 //~^ ERROR failed to resolve: maybe a missing crate `core`
 struct WrongStructAttrStyle {}
 
 #[derive(Diagnostic)]
-#[nonsense(no_crate_example, code = "E0123")]
+#[nonsense(no_crate_example, code = E0123)]
 //~^ ERROR `#[nonsense(...)]` is not a valid attribute
 //~^^ ERROR diagnostic slug not specified
 //~^^^ ERROR cannot find attribute `nonsense` in this scope
 struct InvalidStructAttr {}
 
 #[derive(Diagnostic)]
-#[diag("E0123")]
+#[diag(code = E0123)]
 //~^ ERROR diagnostic slug not specified
 struct InvalidLitNestedAttr {}
 
 #[derive(Diagnostic)]
-#[diag(nonsense, code = "E0123")]
+#[diag(nonsense, code = E0123)]
 //~^ ERROR cannot find value `nonsense` in module `crate::fluent_generated`
 struct InvalidNestedStructAttr {}
 
 #[derive(Diagnostic)]
-#[diag(nonsense("foo"), code = "E0123", slug = "foo")]
+#[diag(nonsense("foo"), code = E0123, slug = "foo")]
 //~^ ERROR diagnostic slug must be the first argument
 //~| ERROR diagnostic slug not specified
 struct InvalidNestedStructAttr1 {}
 
 #[derive(Diagnostic)]
-#[diag(nonsense = "...", code = "E0123", slug = "foo")]
+#[diag(nonsense = "...", code = E0123, slug = "foo")]
 //~^ ERROR unknown argument
 //~| ERROR diagnostic slug not specified
 struct InvalidNestedStructAttr2 {}
 
 #[derive(Diagnostic)]
-#[diag(nonsense = 4, code = "E0123", slug = "foo")]
+#[diag(nonsense = 4, code = E0123, slug = "foo")]
 //~^ ERROR unknown argument
 //~| ERROR diagnostic slug not specified
 struct InvalidNestedStructAttr3 {}
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123", slug = "foo")]
+#[diag(no_crate_example, code = E0123, slug = "foo")]
 //~^ ERROR unknown argument
 struct InvalidNestedStructAttr4 {}
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct WrongPlaceField {
     #[suggestion = "bar"]
     //~^ ERROR `#[suggestion = ...]` is not a valid attribute
@@ -104,19 +108,19 @@ struct WrongPlaceField {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
-#[diag(no_crate_example, code = "E0456")]
+#[diag(no_crate_example, code = E0123)]
+#[diag(no_crate_example, code = E0456)]
 //~^ ERROR specified multiple times
 //~^^ ERROR specified multiple times
 struct DiagSpecifiedTwice {}
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0456", code = "E0457")]
+#[diag(no_crate_example, code = E0123, code = E0456)]
 //~^ ERROR specified multiple times
 struct CodeSpecifiedTwice {}
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, no_crate::example, code = "E0456")]
+#[diag(no_crate_example, no_crate::example, code = E0123)]
 //~^ ERROR diagnostic slug must be the first argument
 struct SlugSpecifiedTwice {}
 
@@ -124,7 +128,7 @@ struct SlugSpecifiedTwice {}
 struct KindNotProvided {} //~ ERROR diagnostic slug not specified
 
 #[derive(Diagnostic)]
-#[diag(code = "E0456")]
+#[diag(code = E0123)]
 //~^ ERROR diagnostic slug not specified
 struct SlugNotProvided {}
 
@@ -133,7 +137,7 @@ struct SlugNotProvided {}
 struct CodeNotProvided {}
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct MessageWrongType {
     #[primary_span]
     //~^ ERROR `#[primary_span]` attribute can only be applied to fields of type `Span` or `MultiSpan`
@@ -141,7 +145,7 @@ struct MessageWrongType {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct InvalidPathFieldAttr {
     #[nonsense]
     //~^ ERROR `#[nonsense]` is not a valid attribute
@@ -150,7 +154,7 @@ struct InvalidPathFieldAttr {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ErrorWithField {
     name: String,
     #[label(no_crate_label)]
@@ -158,7 +162,7 @@ struct ErrorWithField {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ErrorWithMessageAppliedToField {
     #[label(no_crate_label)]
     //~^ ERROR the `#[label(...)]` attribute can only be applied to fields of type `Span` or `MultiSpan`
@@ -166,7 +170,7 @@ struct ErrorWithMessageAppliedToField {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ErrorWithNonexistentField {
     #[suggestion(no_crate_suggestion, code = "{name}")]
     //~^ ERROR `name` doesn't refer to a field on this type
@@ -175,7 +179,7 @@ struct ErrorWithNonexistentField {
 
 #[derive(Diagnostic)]
 //~^ ERROR invalid format string: expected `'}'`
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ErrorMissingClosingBrace {
     #[suggestion(no_crate_suggestion, code = "{name")]
     suggestion: (Span, Applicability),
@@ -185,7 +189,7 @@ struct ErrorMissingClosingBrace {
 
 #[derive(Diagnostic)]
 //~^ ERROR invalid format string: unmatched `}`
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ErrorMissingOpeningBrace {
     #[suggestion(no_crate_suggestion, code = "name}")]
     suggestion: (Span, Applicability),
@@ -194,14 +198,14 @@ struct ErrorMissingOpeningBrace {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct LabelOnSpan {
     #[label(no_crate_label)]
     sp: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct LabelOnNonSpan {
     #[label(no_crate_label)]
     //~^ ERROR the `#[label(...)]` attribute can only be applied to fields of type `Span` or `MultiSpan`
@@ -209,7 +213,7 @@ struct LabelOnNonSpan {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct Suggest {
     #[suggestion(no_crate_suggestion, code = "This is the suggested code")]
     #[suggestion(no_crate_suggestion, code = "This is the suggested code", style = "normal")]
@@ -220,7 +224,7 @@ struct Suggest {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct SuggestWithoutCode {
     #[suggestion(no_crate_suggestion)]
     //~^ ERROR suggestion without `code = "..."`
@@ -228,7 +232,7 @@ struct SuggestWithoutCode {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct SuggestWithBadKey {
     #[suggestion(nonsense = "bar")]
     //~^ ERROR invalid nested attribute
@@ -237,7 +241,7 @@ struct SuggestWithBadKey {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct SuggestWithShorthandMsg {
     #[suggestion(msg = "bar")]
     //~^ ERROR invalid nested attribute
@@ -246,21 +250,21 @@ struct SuggestWithShorthandMsg {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct SuggestWithoutMsg {
     #[suggestion(code = "bar")]
     suggestion: (Span, Applicability),
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct SuggestWithTypesSwapped {
     #[suggestion(no_crate_suggestion, code = "This is suggested code")]
     suggestion: (Applicability, Span),
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct SuggestWithWrongTypeApplicabilityOnly {
     #[suggestion(no_crate_suggestion, code = "This is suggested code")]
     //~^ ERROR wrong field type for suggestion
@@ -268,14 +272,14 @@ struct SuggestWithWrongTypeApplicabilityOnly {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct SuggestWithSpanOnly {
     #[suggestion(no_crate_suggestion, code = "This is suggested code")]
     suggestion: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct SuggestWithDuplicateSpanAndApplicability {
     #[suggestion(no_crate_suggestion, code = "This is suggested code")]
     suggestion: (Span, Span, Applicability),
@@ -283,7 +287,7 @@ struct SuggestWithDuplicateSpanAndApplicability {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct SuggestWithDuplicateApplicabilityAndSpan {
     #[suggestion(no_crate_suggestion, code = "This is suggested code")]
     suggestion: (Applicability, Applicability, Span),
@@ -291,7 +295,7 @@ struct SuggestWithDuplicateApplicabilityAndSpan {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct WrongKindOfAnnotation {
     #[label = "bar"]
     //~^ ERROR `#[label = ...]` is not a valid attribute
@@ -299,7 +303,7 @@ struct WrongKindOfAnnotation {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct OptionsInErrors {
     #[label(no_crate_label)]
     label: Option<Span>,
@@ -308,7 +312,7 @@ struct OptionsInErrors {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0456")]
+#[diag(no_crate_example, code = E0123)]
 struct MoveOutOfBorrowError<'tcx> {
     name: Ident,
     ty: Ty<'tcx>,
@@ -322,7 +326,7 @@ struct MoveOutOfBorrowError<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ErrorWithLifetime<'a> {
     #[label(no_crate_label)]
     span: Span,
@@ -330,7 +334,7 @@ struct ErrorWithLifetime<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ErrorWithDefaultLabelAttr<'a> {
     #[label]
     span: Span,
@@ -338,7 +342,7 @@ struct ErrorWithDefaultLabelAttr<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ArgFieldWithoutSkip {
     #[primary_span]
     span: Span,
@@ -347,7 +351,7 @@ struct ArgFieldWithoutSkip {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ArgFieldWithSkip {
     #[primary_span]
     span: Span,
@@ -358,56 +362,56 @@ struct ArgFieldWithSkip {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ErrorWithSpannedNote {
     #[note]
     span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ErrorWithSpannedNoteCustom {
     #[note(no_crate_note)]
     span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 #[note]
 struct ErrorWithNote {
     val: String,
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 #[note(no_crate_note)]
 struct ErrorWithNoteCustom {
     val: String,
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ErrorWithSpannedHelp {
     #[help]
     span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ErrorWithSpannedHelpCustom {
     #[help(no_crate_help)]
     span: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 #[help]
 struct ErrorWithHelp {
     val: String,
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 #[help(no_crate_help)]
 struct ErrorWithHelpCustom {
     val: String,
@@ -415,34 +419,34 @@ struct ErrorWithHelpCustom {
 
 #[derive(Diagnostic)]
 #[help]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ErrorWithHelpWrongOrder {
     val: String,
 }
 
 #[derive(Diagnostic)]
 #[help(no_crate_help)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ErrorWithHelpCustomWrongOrder {
     val: String,
 }
 
 #[derive(Diagnostic)]
 #[note]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ErrorWithNoteWrongOrder {
     val: String,
 }
 
 #[derive(Diagnostic)]
 #[note(no_crate_note)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ErrorWithNoteCustomWrongOrder {
     val: String,
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ApplicabilityInBoth {
     #[suggestion(no_crate_suggestion, code = "...", applicability = "maybe-incorrect")]
     //~^ ERROR specified multiple times
@@ -450,7 +454,7 @@ struct ApplicabilityInBoth {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct InvalidApplicability {
     #[suggestion(no_crate_suggestion, code = "...", applicability = "batman")]
     //~^ ERROR invalid applicability
@@ -458,14 +462,14 @@ struct InvalidApplicability {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ValidApplicability {
     #[suggestion(no_crate_suggestion, code = "...", applicability = "maybe-incorrect")]
     suggestion: Span,
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct NoApplicability {
     #[suggestion(no_crate_suggestion, code = "...")]
     suggestion: Span,
@@ -483,7 +487,7 @@ struct Subdiagnostic {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct VecField {
     #[primary_span]
     #[label]
@@ -491,7 +495,7 @@ struct VecField {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct UnitField {
     #[primary_span]
     spans: Span,
@@ -502,7 +506,7 @@ struct UnitField {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct OptUnitField {
     #[primary_span]
     spans: Span,
@@ -526,7 +530,7 @@ struct BoolField {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct LabelWithTrailingPath {
     #[label(no_crate_label, foo)]
     //~^ ERROR a diagnostic slug must be the first argument to the attribute
@@ -534,7 +538,7 @@ struct LabelWithTrailingPath {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct LabelWithTrailingNameValue {
     #[label(no_crate_label, foo = "...")]
     //~^ ERROR only `no_span` is a valid nested attribute
@@ -542,7 +546,7 @@ struct LabelWithTrailingNameValue {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct LabelWithTrailingList {
     #[label(no_crate_label, foo("..."))]
     //~^ ERROR only `no_span` is a valid nested attribute
@@ -562,42 +566,42 @@ struct PrimarySpanOnLint {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct ErrorWithMultiSpan {
     #[primary_span]
     span: MultiSpan,
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 #[warning]
 struct ErrorWithWarn {
     val: String,
 }
 
 #[derive(Diagnostic)]
-#[error(no_crate_example, code = "E0123")]
+#[error(no_crate_example, code = E0123)]
 //~^ ERROR `#[error(...)]` is not a valid attribute
 //~| ERROR diagnostic slug not specified
 //~| ERROR cannot find attribute `error` in this scope
 struct ErrorAttribute {}
 
 #[derive(Diagnostic)]
-#[warn_(no_crate_example, code = "E0123")]
+#[warn_(no_crate_example, code = E0123)]
 //~^ ERROR `#[warn_(...)]` is not a valid attribute
 //~| ERROR diagnostic slug not specified
 //~| ERROR cannot find attribute `warn_` in this scope
 struct WarnAttribute {}
 
 #[derive(Diagnostic)]
-#[lint(no_crate_example, code = "E0123")]
+#[lint(no_crate_example, code = E0123)]
 //~^ ERROR `#[lint(...)]` is not a valid attribute
 //~| ERROR diagnostic slug not specified
 //~| ERROR cannot find attribute `lint` in this scope
 struct LintAttributeOnSessionDiag {}
 
 #[derive(LintDiagnostic)]
-#[lint(no_crate_example, code = "E0123")]
+#[lint(no_crate_example, code = E0123)]
 //~^ ERROR `#[lint(...)]` is not a valid attribute
 //~| ERROR `#[lint(...)]` is not a valid attribute
 //~| ERROR diagnostic slug not specified
@@ -605,7 +609,7 @@ struct LintAttributeOnSessionDiag {}
 struct LintAttributeOnLintDiag {}
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct DuplicatedSuggestionCode {
     #[suggestion(no_crate_suggestion, code = "...", code = ",,,")]
     //~^ ERROR specified multiple times
@@ -613,7 +617,7 @@ struct DuplicatedSuggestionCode {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct InvalidTypeInSuggestionTuple {
     #[suggestion(no_crate_suggestion, code = "...")]
     suggestion: (Span, usize),
@@ -621,7 +625,7 @@ struct InvalidTypeInSuggestionTuple {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct MissingApplicabilityInSuggestionTuple {
     #[suggestion(no_crate_suggestion, code = "...")]
     suggestion: (Span,),
@@ -629,7 +633,7 @@ struct MissingApplicabilityInSuggestionTuple {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct MissingCodeInSuggestion {
     #[suggestion(no_crate_suggestion)]
     //~^ ERROR suggestion without `code = "..."`
@@ -637,7 +641,7 @@ struct MissingCodeInSuggestion {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 #[multipart_suggestion(no_crate_suggestion)]
 //~^ ERROR `#[multipart_suggestion(...)]` is not a valid attribute
 //~| ERROR cannot find attribute `multipart_suggestion` in this scope
@@ -652,7 +656,7 @@ struct MultipartSuggestion {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 #[suggestion(no_crate_suggestion, code = "...")]
 //~^ ERROR `#[suggestion(...)]` is not a valid attribute
 struct SuggestionOnStruct {
@@ -661,7 +665,7 @@ struct SuggestionOnStruct {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 #[label]
 //~^ ERROR `#[label]` is not a valid attribute
 struct LabelOnStruct {
@@ -688,7 +692,7 @@ enum ExampleEnum {
 }
 
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct RawIdentDiagnosticArg {
     pub r#type: String,
 }
@@ -762,7 +766,7 @@ struct SubdiagnosticEagerSuggestion {
 
 /// with a doc comment on the type..
 #[derive(Diagnostic)]
-#[diag(no_crate_example, code = "E0123")]
+#[diag(no_crate_example, code = E0123)]
 struct WithDocComment {
     /// ..and the field
     #[primary_span]
diff --git a/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr b/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr
index f376c034587..67257c28b6e 100644
--- a/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr
+++ b/tests/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr
@@ -1,11 +1,11 @@
 error: unsupported type attribute for diagnostic derive enum
-  --> $DIR/diagnostic-derive.rs:43:1
+  --> $DIR/diagnostic-derive.rs:47:1
    |
-LL | #[diag(no_crate_example, code = "E0123")]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | #[diag(no_crate_example, code = E0123)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: diagnostic slug not specified
-  --> $DIR/diagnostic-derive.rs:46:5
+  --> $DIR/diagnostic-derive.rs:50:5
    |
 LL |     Foo,
    |     ^^^
@@ -13,7 +13,7 @@ LL |     Foo,
    = help: specify the slug as the first argument to the `#[diag(...)]` attribute, such as `#[diag(hir_analysis_example_error)]`
 
 error: diagnostic slug not specified
-  --> $DIR/diagnostic-derive.rs:48:5
+  --> $DIR/diagnostic-derive.rs:52:5
    |
 LL |     Bar,
    |     ^^^
@@ -21,15 +21,15 @@ LL |     Bar,
    = help: specify the slug as the first argument to the `#[diag(...)]` attribute, such as `#[diag(hir_analysis_example_error)]`
 
 error: `#[nonsense(...)]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:59:1
+  --> $DIR/diagnostic-derive.rs:63:1
    |
-LL | #[nonsense(no_crate_example, code = "E0123")]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | #[nonsense(no_crate_example, code = E0123)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: diagnostic slug not specified
-  --> $DIR/diagnostic-derive.rs:59:1
+  --> $DIR/diagnostic-derive.rs:63:1
    |
-LL | / #[nonsense(no_crate_example, code = "E0123")]
+LL | / #[nonsense(no_crate_example, code = E0123)]
 LL | |
 LL | |
 LL | |
@@ -39,9 +39,9 @@ LL | | struct InvalidStructAttr {}
    = help: specify the slug as the first argument to the `#[diag(...)]` attribute, such as `#[diag(hir_analysis_example_error)]`
 
 error: diagnostic slug not specified
-  --> $DIR/diagnostic-derive.rs:66:1
+  --> $DIR/diagnostic-derive.rs:70:1
    |
-LL | / #[diag("E0123")]
+LL | / #[diag(code = E0123)]
 LL | |
 LL | | struct InvalidLitNestedAttr {}
    | |______________________________^
@@ -49,15 +49,15 @@ LL | | struct InvalidLitNestedAttr {}
    = help: specify the slug as the first argument to the `#[diag(...)]` attribute, such as `#[diag(hir_analysis_example_error)]`
 
 error: diagnostic slug must be the first argument
-  --> $DIR/diagnostic-derive.rs:76:16
+  --> $DIR/diagnostic-derive.rs:80:16
    |
-LL | #[diag(nonsense("foo"), code = "E0123", slug = "foo")]
+LL | #[diag(nonsense("foo"), code = E0123, slug = "foo")]
    |                ^
 
 error: diagnostic slug not specified
-  --> $DIR/diagnostic-derive.rs:76:1
+  --> $DIR/diagnostic-derive.rs:80:1
    |
-LL | / #[diag(nonsense("foo"), code = "E0123", slug = "foo")]
+LL | / #[diag(nonsense("foo"), code = E0123, slug = "foo")]
 LL | |
 LL | |
 LL | | struct InvalidNestedStructAttr1 {}
@@ -66,17 +66,17 @@ LL | | struct InvalidNestedStructAttr1 {}
    = help: specify the slug as the first argument to the `#[diag(...)]` attribute, such as `#[diag(hir_analysis_example_error)]`
 
 error: unknown argument
-  --> $DIR/diagnostic-derive.rs:82:8
+  --> $DIR/diagnostic-derive.rs:86:8
    |
-LL | #[diag(nonsense = "...", code = "E0123", slug = "foo")]
+LL | #[diag(nonsense = "...", code = E0123, slug = "foo")]
    |        ^^^^^^^^
    |
    = note: only the `code` parameter is valid after the slug
 
 error: diagnostic slug not specified
-  --> $DIR/diagnostic-derive.rs:82:1
+  --> $DIR/diagnostic-derive.rs:86:1
    |
-LL | / #[diag(nonsense = "...", code = "E0123", slug = "foo")]
+LL | / #[diag(nonsense = "...", code = E0123, slug = "foo")]
 LL | |
 LL | |
 LL | | struct InvalidNestedStructAttr2 {}
@@ -85,17 +85,17 @@ LL | | struct InvalidNestedStructAttr2 {}
    = help: specify the slug as the first argument to the `#[diag(...)]` attribute, such as `#[diag(hir_analysis_example_error)]`
 
 error: unknown argument
-  --> $DIR/diagnostic-derive.rs:88:8
+  --> $DIR/diagnostic-derive.rs:92:8
    |
-LL | #[diag(nonsense = 4, code = "E0123", slug = "foo")]
+LL | #[diag(nonsense = 4, code = E0123, slug = "foo")]
    |        ^^^^^^^^
    |
    = note: only the `code` parameter is valid after the slug
 
 error: diagnostic slug not specified
-  --> $DIR/diagnostic-derive.rs:88:1
+  --> $DIR/diagnostic-derive.rs:92:1
    |
-LL | / #[diag(nonsense = 4, code = "E0123", slug = "foo")]
+LL | / #[diag(nonsense = 4, code = E0123, slug = "foo")]
 LL | |
 LL | |
 LL | | struct InvalidNestedStructAttr3 {}
@@ -104,63 +104,63 @@ LL | | struct InvalidNestedStructAttr3 {}
    = help: specify the slug as the first argument to the `#[diag(...)]` attribute, such as `#[diag(hir_analysis_example_error)]`
 
 error: unknown argument
-  --> $DIR/diagnostic-derive.rs:94:42
+  --> $DIR/diagnostic-derive.rs:98:40
    |
-LL | #[diag(no_crate_example, code = "E0123", slug = "foo")]
-   |                                          ^^^^
+LL | #[diag(no_crate_example, code = E0123, slug = "foo")]
+   |                                        ^^^^
    |
    = note: only the `code` parameter is valid after the slug
 
 error: `#[suggestion = ...]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:101:5
+  --> $DIR/diagnostic-derive.rs:105:5
    |
 LL |     #[suggestion = "bar"]
    |     ^^^^^^^^^^^^^^^^^^^^^
 
 error: specified multiple times
-  --> $DIR/diagnostic-derive.rs:108:8
+  --> $DIR/diagnostic-derive.rs:112:8
    |
-LL | #[diag(no_crate_example, code = "E0456")]
+LL | #[diag(no_crate_example, code = E0456)]
    |        ^^^^^^^^^^^^^^^^
    |
 note: previously specified here
-  --> $DIR/diagnostic-derive.rs:107:8
+  --> $DIR/diagnostic-derive.rs:111:8
    |
-LL | #[diag(no_crate_example, code = "E0123")]
+LL | #[diag(no_crate_example, code = E0123)]
    |        ^^^^^^^^^^^^^^^^
 
 error: specified multiple times
-  --> $DIR/diagnostic-derive.rs:108:26
+  --> $DIR/diagnostic-derive.rs:112:26
    |
-LL | #[diag(no_crate_example, code = "E0456")]
+LL | #[diag(no_crate_example, code = E0456)]
    |                          ^^^^
    |
 note: previously specified here
-  --> $DIR/diagnostic-derive.rs:107:26
+  --> $DIR/diagnostic-derive.rs:111:26
    |
-LL | #[diag(no_crate_example, code = "E0123")]
+LL | #[diag(no_crate_example, code = E0123)]
    |                          ^^^^
 
 error: specified multiple times
-  --> $DIR/diagnostic-derive.rs:114:42
+  --> $DIR/diagnostic-derive.rs:118:40
    |
-LL | #[diag(no_crate_example, code = "E0456", code = "E0457")]
-   |                                          ^^^^
+LL | #[diag(no_crate_example, code = E0123, code = E0456)]
+   |                                        ^^^^
    |
 note: previously specified here
-  --> $DIR/diagnostic-derive.rs:114:26
+  --> $DIR/diagnostic-derive.rs:118:26
    |
-LL | #[diag(no_crate_example, code = "E0456", code = "E0457")]
+LL | #[diag(no_crate_example, code = E0123, code = E0456)]
    |                          ^^^^
 
 error: diagnostic slug must be the first argument
-  --> $DIR/diagnostic-derive.rs:119:43
+  --> $DIR/diagnostic-derive.rs:123:43
    |
-LL | #[diag(no_crate_example, no_crate::example, code = "E0456")]
+LL | #[diag(no_crate_example, no_crate::example, code = E0123)]
    |                                           ^
 
 error: diagnostic slug not specified
-  --> $DIR/diagnostic-derive.rs:124:1
+  --> $DIR/diagnostic-derive.rs:128:1
    |
 LL | struct KindNotProvided {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -168,9 +168,9 @@ LL | struct KindNotProvided {}
    = help: specify the slug as the first argument to the `#[diag(...)]` attribute, such as `#[diag(hir_analysis_example_error)]`
 
 error: diagnostic slug not specified
-  --> $DIR/diagnostic-derive.rs:127:1
+  --> $DIR/diagnostic-derive.rs:131:1
    |
-LL | / #[diag(code = "E0456")]
+LL | / #[diag(code = E0123)]
 LL | |
 LL | | struct SlugNotProvided {}
    | |_________________________^
@@ -178,31 +178,31 @@ LL | | struct SlugNotProvided {}
    = help: specify the slug as the first argument to the `#[diag(...)]` attribute, such as `#[diag(hir_analysis_example_error)]`
 
 error: the `#[primary_span]` attribute can only be applied to fields of type `Span` or `MultiSpan`
-  --> $DIR/diagnostic-derive.rs:138:5
+  --> $DIR/diagnostic-derive.rs:142:5
    |
 LL |     #[primary_span]
    |     ^^^^^^^^^^^^^^^
 
 error: `#[nonsense]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:146:5
+  --> $DIR/diagnostic-derive.rs:150:5
    |
 LL |     #[nonsense]
    |     ^^^^^^^^^^^
 
 error: the `#[label(...)]` attribute can only be applied to fields of type `Span` or `MultiSpan`
-  --> $DIR/diagnostic-derive.rs:163:5
+  --> $DIR/diagnostic-derive.rs:167:5
    |
 LL |     #[label(no_crate_label)]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: `name` doesn't refer to a field on this type
-  --> $DIR/diagnostic-derive.rs:171:46
+  --> $DIR/diagnostic-derive.rs:175:46
    |
 LL |     #[suggestion(no_crate_suggestion, code = "{name}")]
    |                                              ^^^^^^^^
 
 error: invalid format string: expected `'}'` but string was terminated
-  --> $DIR/diagnostic-derive.rs:176:10
+  --> $DIR/diagnostic-derive.rs:180:10
    |
 LL | #[derive(Diagnostic)]
    |          ^^^^^^^^^^ expected `'}'` in format string
@@ -211,7 +211,7 @@ LL | #[derive(Diagnostic)]
    = note: this error originates in the derive macro `Diagnostic` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: invalid format string: unmatched `}` found
-  --> $DIR/diagnostic-derive.rs:186:10
+  --> $DIR/diagnostic-derive.rs:190:10
    |
 LL | #[derive(Diagnostic)]
    |          ^^^^^^^^^^ unmatched `}` in format string
@@ -220,19 +220,19 @@ LL | #[derive(Diagnostic)]
    = note: this error originates in the derive macro `Diagnostic` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: the `#[label(...)]` attribute can only be applied to fields of type `Span` or `MultiSpan`
-  --> $DIR/diagnostic-derive.rs:206:5
+  --> $DIR/diagnostic-derive.rs:210:5
    |
 LL |     #[label(no_crate_label)]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: suggestion without `code = "..."`
-  --> $DIR/diagnostic-derive.rs:225:5
+  --> $DIR/diagnostic-derive.rs:229:5
    |
 LL |     #[suggestion(no_crate_suggestion)]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: invalid nested attribute
-  --> $DIR/diagnostic-derive.rs:233:18
+  --> $DIR/diagnostic-derive.rs:237:18
    |
 LL |     #[suggestion(nonsense = "bar")]
    |                  ^^^^^^^^
@@ -240,13 +240,13 @@ LL |     #[suggestion(nonsense = "bar")]
    = help: only `no_span`, `style`, `code` and `applicability` are valid nested attributes
 
 error: suggestion without `code = "..."`
-  --> $DIR/diagnostic-derive.rs:233:5
+  --> $DIR/diagnostic-derive.rs:237:5
    |
 LL |     #[suggestion(nonsense = "bar")]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: invalid nested attribute
-  --> $DIR/diagnostic-derive.rs:242:18
+  --> $DIR/diagnostic-derive.rs:246:18
    |
 LL |     #[suggestion(msg = "bar")]
    |                  ^^^
@@ -254,13 +254,13 @@ LL |     #[suggestion(msg = "bar")]
    = help: only `no_span`, `style`, `code` and `applicability` are valid nested attributes
 
 error: suggestion without `code = "..."`
-  --> $DIR/diagnostic-derive.rs:242:5
+  --> $DIR/diagnostic-derive.rs:246:5
    |
 LL |     #[suggestion(msg = "bar")]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: wrong field type for suggestion
-  --> $DIR/diagnostic-derive.rs:265:5
+  --> $DIR/diagnostic-derive.rs:269:5
    |
 LL | /     #[suggestion(no_crate_suggestion, code = "This is suggested code")]
 LL | |
@@ -270,79 +270,79 @@ LL | |     suggestion: Applicability,
    = help: `#[suggestion(...)]` should be applied to fields of type `Span` or `(Span, Applicability)`
 
 error: specified multiple times
-  --> $DIR/diagnostic-derive.rs:281:24
+  --> $DIR/diagnostic-derive.rs:285:24
    |
 LL |     suggestion: (Span, Span, Applicability),
    |                        ^^^^
    |
 note: previously specified here
-  --> $DIR/diagnostic-derive.rs:281:18
+  --> $DIR/diagnostic-derive.rs:285:18
    |
 LL |     suggestion: (Span, Span, Applicability),
    |                  ^^^^
 
 error: specified multiple times
-  --> $DIR/diagnostic-derive.rs:289:33
+  --> $DIR/diagnostic-derive.rs:293:33
    |
 LL |     suggestion: (Applicability, Applicability, Span),
    |                                 ^^^^^^^^^^^^^
    |
 note: previously specified here
-  --> $DIR/diagnostic-derive.rs:289:18
+  --> $DIR/diagnostic-derive.rs:293:18
    |
 LL |     suggestion: (Applicability, Applicability, Span),
    |                  ^^^^^^^^^^^^^
 
 error: `#[label = ...]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:296:5
+  --> $DIR/diagnostic-derive.rs:300:5
    |
 LL |     #[label = "bar"]
    |     ^^^^^^^^^^^^^^^^
 
 error: specified multiple times
-  --> $DIR/diagnostic-derive.rs:447:5
+  --> $DIR/diagnostic-derive.rs:451:5
    |
 LL |     #[suggestion(no_crate_suggestion, code = "...", applicability = "maybe-incorrect")]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: previously specified here
-  --> $DIR/diagnostic-derive.rs:449:24
+  --> $DIR/diagnostic-derive.rs:453:24
    |
 LL |     suggestion: (Span, Applicability),
    |                        ^^^^^^^^^^^^^
 
 error: invalid applicability
-  --> $DIR/diagnostic-derive.rs:455:69
+  --> $DIR/diagnostic-derive.rs:459:69
    |
 LL |     #[suggestion(no_crate_suggestion, code = "...", applicability = "batman")]
    |                                                                     ^^^^^^^^
 
 error: the `#[help(...)]` attribute can only be applied to fields of type `Span`, `MultiSpan`, `bool` or `()`
-  --> $DIR/diagnostic-derive.rs:522:5
+  --> $DIR/diagnostic-derive.rs:526:5
    |
 LL |     #[help(no_crate_help)]
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 error: a diagnostic slug must be the first argument to the attribute
-  --> $DIR/diagnostic-derive.rs:531:32
+  --> $DIR/diagnostic-derive.rs:535:32
    |
 LL |     #[label(no_crate_label, foo)]
    |                                ^
 
 error: only `no_span` is a valid nested attribute
-  --> $DIR/diagnostic-derive.rs:539:29
+  --> $DIR/diagnostic-derive.rs:543:29
    |
 LL |     #[label(no_crate_label, foo = "...")]
    |                             ^^^
 
 error: only `no_span` is a valid nested attribute
-  --> $DIR/diagnostic-derive.rs:547:29
+  --> $DIR/diagnostic-derive.rs:551:29
    |
 LL |     #[label(no_crate_label, foo("..."))]
    |                             ^^^
 
 error: `#[primary_span]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:559:5
+  --> $DIR/diagnostic-derive.rs:563:5
    |
 LL |     #[primary_span]
    |     ^^^^^^^^^^^^^^^
@@ -350,15 +350,15 @@ LL |     #[primary_span]
    = help: the `primary_span` field attribute is not valid for lint diagnostics
 
 error: `#[error(...)]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:579:1
+  --> $DIR/diagnostic-derive.rs:583:1
    |
-LL | #[error(no_crate_example, code = "E0123")]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | #[error(no_crate_example, code = E0123)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: diagnostic slug not specified
-  --> $DIR/diagnostic-derive.rs:579:1
+  --> $DIR/diagnostic-derive.rs:583:1
    |
-LL | / #[error(no_crate_example, code = "E0123")]
+LL | / #[error(no_crate_example, code = E0123)]
 LL | |
 LL | |
 LL | |
@@ -368,15 +368,15 @@ LL | | struct ErrorAttribute {}
    = help: specify the slug as the first argument to the `#[diag(...)]` attribute, such as `#[diag(hir_analysis_example_error)]`
 
 error: `#[warn_(...)]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:586:1
+  --> $DIR/diagnostic-derive.rs:590:1
    |
-LL | #[warn_(no_crate_example, code = "E0123")]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | #[warn_(no_crate_example, code = E0123)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: diagnostic slug not specified
-  --> $DIR/diagnostic-derive.rs:586:1
+  --> $DIR/diagnostic-derive.rs:590:1
    |
-LL | / #[warn_(no_crate_example, code = "E0123")]
+LL | / #[warn_(no_crate_example, code = E0123)]
 LL | |
 LL | |
 LL | |
@@ -386,15 +386,15 @@ LL | | struct WarnAttribute {}
    = help: specify the slug as the first argument to the `#[diag(...)]` attribute, such as `#[diag(hir_analysis_example_error)]`
 
 error: `#[lint(...)]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:593:1
+  --> $DIR/diagnostic-derive.rs:597:1
    |
-LL | #[lint(no_crate_example, code = "E0123")]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | #[lint(no_crate_example, code = E0123)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: diagnostic slug not specified
-  --> $DIR/diagnostic-derive.rs:593:1
+  --> $DIR/diagnostic-derive.rs:597:1
    |
-LL | / #[lint(no_crate_example, code = "E0123")]
+LL | / #[lint(no_crate_example, code = E0123)]
 LL | |
 LL | |
 LL | |
@@ -404,23 +404,23 @@ LL | | struct LintAttributeOnSessionDiag {}
    = help: specify the slug as the first argument to the `#[diag(...)]` attribute, such as `#[diag(hir_analysis_example_error)]`
 
 error: `#[lint(...)]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:600:1
+  --> $DIR/diagnostic-derive.rs:604:1
    |
-LL | #[lint(no_crate_example, code = "E0123")]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | #[lint(no_crate_example, code = E0123)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: `#[lint(...)]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:600:1
+  --> $DIR/diagnostic-derive.rs:604:1
    |
-LL | #[lint(no_crate_example, code = "E0123")]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | #[lint(no_crate_example, code = E0123)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: diagnostic slug not specified
-  --> $DIR/diagnostic-derive.rs:600:1
+  --> $DIR/diagnostic-derive.rs:604:1
    |
-LL | / #[lint(no_crate_example, code = "E0123")]
+LL | / #[lint(no_crate_example, code = E0123)]
 LL | |
 LL | |
 LL | |
@@ -431,19 +431,19 @@ LL | | struct LintAttributeOnLintDiag {}
    = help: specify the slug as the first argument to the attribute, such as `#[diag(compiletest_example)]`
 
 error: specified multiple times
-  --> $DIR/diagnostic-derive.rs:610:53
+  --> $DIR/diagnostic-derive.rs:614:53
    |
 LL |     #[suggestion(no_crate_suggestion, code = "...", code = ",,,")]
    |                                                     ^^^^
    |
 note: previously specified here
-  --> $DIR/diagnostic-derive.rs:610:39
+  --> $DIR/diagnostic-derive.rs:614:39
    |
 LL |     #[suggestion(no_crate_suggestion, code = "...", code = ",,,")]
    |                                       ^^^^
 
 error: wrong types for suggestion
-  --> $DIR/diagnostic-derive.rs:619:24
+  --> $DIR/diagnostic-derive.rs:623:24
    |
 LL |     suggestion: (Span, usize),
    |                        ^^^^^
@@ -451,7 +451,7 @@ LL |     suggestion: (Span, usize),
    = help: `#[suggestion(...)]` on a tuple field must be applied to fields of type `(Span, Applicability)`
 
 error: wrong types for suggestion
-  --> $DIR/diagnostic-derive.rs:627:17
+  --> $DIR/diagnostic-derive.rs:631:17
    |
 LL |     suggestion: (Span,),
    |                 ^^^^^^^
@@ -459,13 +459,13 @@ LL |     suggestion: (Span,),
    = help: `#[suggestion(...)]` on a tuple field must be applied to fields of type `(Span, Applicability)`
 
 error: suggestion without `code = "..."`
-  --> $DIR/diagnostic-derive.rs:634:5
+  --> $DIR/diagnostic-derive.rs:638:5
    |
 LL |     #[suggestion(no_crate_suggestion)]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: `#[multipart_suggestion(...)]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:641:1
+  --> $DIR/diagnostic-derive.rs:645:1
    |
 LL | #[multipart_suggestion(no_crate_suggestion)]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -473,7 +473,7 @@ LL | #[multipart_suggestion(no_crate_suggestion)]
    = help: consider creating a `Subdiagnostic` instead
 
 error: `#[multipart_suggestion(...)]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:644:1
+  --> $DIR/diagnostic-derive.rs:648:1
    |
 LL | #[multipart_suggestion()]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -481,7 +481,7 @@ LL | #[multipart_suggestion()]
    = help: consider creating a `Subdiagnostic` instead
 
 error: `#[multipart_suggestion(...)]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:648:5
+  --> $DIR/diagnostic-derive.rs:652:5
    |
 LL |     #[multipart_suggestion(no_crate_suggestion)]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -489,7 +489,7 @@ LL |     #[multipart_suggestion(no_crate_suggestion)]
    = help: consider creating a `Subdiagnostic` instead
 
 error: `#[suggestion(...)]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:656:1
+  --> $DIR/diagnostic-derive.rs:660:1
    |
 LL | #[suggestion(no_crate_suggestion, code = "...")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -497,7 +497,7 @@ LL | #[suggestion(no_crate_suggestion, code = "...")]
    = help: `#[label]` and `#[suggestion]` can only be applied to fields
 
 error: `#[label]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:665:1
+  --> $DIR/diagnostic-derive.rs:669:1
    |
 LL | #[label]
    | ^^^^^^^^
@@ -505,31 +505,31 @@ LL | #[label]
    = help: `#[label]` and `#[suggestion]` can only be applied to fields
 
 error: `eager` is the only supported nested attribute for `subdiagnostic`
-  --> $DIR/diagnostic-derive.rs:699:7
+  --> $DIR/diagnostic-derive.rs:703:7
    |
 LL |     #[subdiagnostic(bad)]
    |       ^^^^^^^^^^^^^^^^^^
 
 error: `#[subdiagnostic = ...]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:707:5
+  --> $DIR/diagnostic-derive.rs:711:5
    |
 LL |     #[subdiagnostic = "bad"]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: `eager` is the only supported nested attribute for `subdiagnostic`
-  --> $DIR/diagnostic-derive.rs:715:7
+  --> $DIR/diagnostic-derive.rs:719:7
    |
 LL |     #[subdiagnostic(bad, bad)]
    |       ^^^^^^^^^^^^^^^^^^^^^^^
 
 error: `eager` is the only supported nested attribute for `subdiagnostic`
-  --> $DIR/diagnostic-derive.rs:723:7
+  --> $DIR/diagnostic-derive.rs:727:7
    |
 LL |     #[subdiagnostic("bad")]
    |       ^^^^^^^^^^^^^^^^^^^^
 
 error: `#[subdiagnostic(...)]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:731:5
+  --> $DIR/diagnostic-derive.rs:735:5
    |
 LL |     #[subdiagnostic(eager)]
    |     ^^^^^^^^^^^^^^^^^^^^^^^
@@ -537,19 +537,19 @@ LL |     #[subdiagnostic(eager)]
    = help: eager subdiagnostics are not supported on lints
 
 error: expected at least one string literal for `code(...)`
-  --> $DIR/diagnostic-derive.rs:789:23
+  --> $DIR/diagnostic-derive.rs:793:23
    |
 LL |     #[suggestion(code())]
    |                       ^
 
 error: `code(...)` must contain only string literals
-  --> $DIR/diagnostic-derive.rs:797:23
+  --> $DIR/diagnostic-derive.rs:801:23
    |
 LL |     #[suggestion(code(foo))]
    |                       ^^^
 
 error: `#[suggestion(...)]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:821:5
+  --> $DIR/diagnostic-derive.rs:825:5
    |
 LL |     #[suggestion(no_crate_suggestion, code = "")]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -559,85 +559,85 @@ LL |     #[suggestion(no_crate_suggestion, code = "")]
    = help: to show a variable set of suggestions, use a `Vec` of `Subdiagnostic`s annotated with `#[suggestion(...)]`
 
 error[E0433]: failed to resolve: maybe a missing crate `core`?
-  --> $DIR/diagnostic-derive.rs:54:8
+  --> $DIR/diagnostic-derive.rs:58:8
    |
 LL | #[diag = "E0123"]
    |        ^ maybe a missing crate `core`?
 
 error[E0433]: failed to resolve: maybe a missing crate `core`?
-  --> $DIR/diagnostic-derive.rs:797:23
+  --> $DIR/diagnostic-derive.rs:801:23
    |
 LL |     #[suggestion(code(foo))]
    |                       ^^^ maybe a missing crate `core`?
 
 error[E0433]: failed to resolve: maybe a missing crate `core`?
-  --> $DIR/diagnostic-derive.rs:806:25
+  --> $DIR/diagnostic-derive.rs:810:25
    |
 LL |     #[suggestion(code = 3)]
    |                         ^ maybe a missing crate `core`?
 
 error: cannot find attribute `nonsense` in this scope
-  --> $DIR/diagnostic-derive.rs:59:3
+  --> $DIR/diagnostic-derive.rs:63:3
    |
-LL | #[nonsense(no_crate_example, code = "E0123")]
+LL | #[nonsense(no_crate_example, code = E0123)]
    |   ^^^^^^^^
 
 error: cannot find attribute `nonsense` in this scope
-  --> $DIR/diagnostic-derive.rs:146:7
+  --> $DIR/diagnostic-derive.rs:150:7
    |
 LL |     #[nonsense]
    |       ^^^^^^^^
 
 error: cannot find attribute `error` in this scope
-  --> $DIR/diagnostic-derive.rs:579:3
+  --> $DIR/diagnostic-derive.rs:583:3
    |
-LL | #[error(no_crate_example, code = "E0123")]
+LL | #[error(no_crate_example, code = E0123)]
    |   ^^^^^
 
 error: cannot find attribute `warn_` in this scope
-  --> $DIR/diagnostic-derive.rs:586:3
+  --> $DIR/diagnostic-derive.rs:590:3
    |
-LL | #[warn_(no_crate_example, code = "E0123")]
+LL | #[warn_(no_crate_example, code = E0123)]
    |   ^^^^^ help: a built-in attribute with a similar name exists: `warn`
 
 error: cannot find attribute `lint` in this scope
-  --> $DIR/diagnostic-derive.rs:593:3
+  --> $DIR/diagnostic-derive.rs:597:3
    |
-LL | #[lint(no_crate_example, code = "E0123")]
+LL | #[lint(no_crate_example, code = E0123)]
    |   ^^^^ help: a built-in attribute with a similar name exists: `link`
 
 error: cannot find attribute `lint` in this scope
-  --> $DIR/diagnostic-derive.rs:600:3
+  --> $DIR/diagnostic-derive.rs:604:3
    |
-LL | #[lint(no_crate_example, code = "E0123")]
+LL | #[lint(no_crate_example, code = E0123)]
    |   ^^^^ help: a built-in attribute with a similar name exists: `link`
 
 error: cannot find attribute `multipart_suggestion` in this scope
-  --> $DIR/diagnostic-derive.rs:641:3
+  --> $DIR/diagnostic-derive.rs:645:3
    |
 LL | #[multipart_suggestion(no_crate_suggestion)]
    |   ^^^^^^^^^^^^^^^^^^^^
 
 error: cannot find attribute `multipart_suggestion` in this scope
-  --> $DIR/diagnostic-derive.rs:644:3
+  --> $DIR/diagnostic-derive.rs:648:3
    |
 LL | #[multipart_suggestion()]
    |   ^^^^^^^^^^^^^^^^^^^^
 
 error: cannot find attribute `multipart_suggestion` in this scope
-  --> $DIR/diagnostic-derive.rs:648:7
+  --> $DIR/diagnostic-derive.rs:652:7
    |
 LL |     #[multipart_suggestion(no_crate_suggestion)]
    |       ^^^^^^^^^^^^^^^^^^^^
 
 error[E0425]: cannot find value `nonsense` in module `crate::fluent_generated`
-  --> $DIR/diagnostic-derive.rs:71:8
+  --> $DIR/diagnostic-derive.rs:75:8
    |
-LL | #[diag(nonsense, code = "E0123")]
+LL | #[diag(nonsense, code = E0123)]
    |        ^^^^^^^^ not found in `crate::fluent_generated`
 
 error[E0425]: cannot find value `__code_34` in this scope
-  --> $DIR/diagnostic-derive.rs:803:10
+  --> $DIR/diagnostic-derive.rs:807:10
    |
 LL | #[derive(Diagnostic)]
    |          ^^^^^^^^^^ not found in this scope
@@ -645,7 +645,7 @@ LL | #[derive(Diagnostic)]
    = note: this error originates in the derive macro `Diagnostic` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0277]: the trait bound `Hello: IntoDiagnosticArg` is not satisfied
-  --> $DIR/diagnostic-derive.rs:345:12
+  --> $DIR/diagnostic-derive.rs:349:12
    |
 LL | #[derive(Diagnostic)]
    |          ---------- required by a bound introduced by this call
diff --git a/tests/ui-fulldeps/session-diagnostic/enforce_slug_naming.rs b/tests/ui-fulldeps/session-diagnostic/enforce_slug_naming.rs
index a0a8114e0c5..785da11b9b2 100644
--- a/tests/ui-fulldeps/session-diagnostic/enforce_slug_naming.rs
+++ b/tests/ui-fulldeps/session-diagnostic/enforce_slug_naming.rs
@@ -19,6 +19,6 @@
 extern crate rustc_session;
 
 #[derive(Diagnostic)]
-#[diag(compiletest_example, code = "E0123")]
+#[diag(compiletest_example, code = 0123)]
 //~^ ERROR diagnostic slug and crate name do not match
 struct Hello {}
diff --git a/tests/ui-fulldeps/session-diagnostic/enforce_slug_naming.stderr b/tests/ui-fulldeps/session-diagnostic/enforce_slug_naming.stderr
index 4cdc24e6a6b..eda24a555f8 100644
--- a/tests/ui-fulldeps/session-diagnostic/enforce_slug_naming.stderr
+++ b/tests/ui-fulldeps/session-diagnostic/enforce_slug_naming.stderr
@@ -1,7 +1,7 @@
 error: diagnostic slug and crate name do not match
   --> $DIR/enforce_slug_naming.rs:22:8
    |
-LL | #[diag(compiletest_example, code = "E0123")]
+LL | #[diag(compiletest_example, code = 0123)]
    |        ^^^^^^^^^^^^^^^^^^^
    |
    = note: slug is `compiletest_example` but the crate name is `rustc_dummy`
diff --git a/triagebot.toml b/triagebot.toml
index c46f9c90030..e57dd158374 100644
--- a/triagebot.toml
+++ b/triagebot.toml
@@ -476,7 +476,7 @@ of `ObligationCtxt`.
 """
 cc = ["@lcnr", "@compiler-errors"]
 
-[mentions."compiler/rustc_error_codes/src/error_codes.rs"]
+[mentions."compiler/rustc_error_codes/src/lib.rs"]
 message = "Some changes occurred in diagnostic error codes"
 cc = ["@GuillaumeGomez"]