UPDATE - into_diagnostic to take a Handler instead of a ParseSess

Suggested by the team in this Zulip Topic https://rust-lang.zulipchat.com/#narrow/stream/336883-i18n/topic/.23100717.20SessionDiagnostic.20on.20Handler

Handler already has almost all the capabilities of ParseSess when it comes to diagnostic emission, in this migration we only needed to add the ability to access source_map from the emitter in order to get a Snippet and the start_point. Not sure if this is the best way to address this gap

compiler/rustc_attr/src/session_diagnostics.rs

@@ -1,9 +1,11 @@
 use std::num::IntErrorKind;
 
 use rustc_ast as ast;
-use rustc_errors::{error_code, fluent, Applicability, DiagnosticBuilder, ErrorGuaranteed};
+use rustc_errors::{
+    error_code, fluent, Applicability, DiagnosticBuilder, ErrorGuaranteed, Handler,
+};
 use rustc_macros::SessionDiagnostic;
-use rustc_session::{parse::ParseSess, SessionDiagnostic};
+use rustc_session::SessionDiagnostic;
 use rustc_span::{Span, Symbol};
 
 use crate::UnsupportedLiteralReason;
@@ -49,9 +51,9 @@ pub(crate) struct UnknownMetaItem<'a> {
 
 // Manual implementation to be able to format `expected` items correctly.
 impl<'a> SessionDiagnostic<'a> for UnknownMetaItem<'_> {
-    fn into_diagnostic(self, sess: &'a ParseSess) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+    fn into_diagnostic(self, handler: &'a Handler) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
         let expected = self.expected.iter().map(|name| format!("`{}`", name)).collect::<Vec<_>>();
-        let mut diag = sess.span_diagnostic.struct_span_err_with_code(
+        let mut diag = handler.struct_span_err_with_code(
             self.span,
             fluent::attr::unknown_meta_item,
             error_code!(E0541),
@@ -207,8 +209,8 @@ pub(crate) struct UnsupportedLiteral {
 }
 
 impl<'a> SessionDiagnostic<'a> for UnsupportedLiteral {
-    fn into_diagnostic(self, sess: &'a ParseSess) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+    fn into_diagnostic(self, handler: &'a Handler) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
-        let mut diag = sess.span_diagnostic.struct_span_err_with_code(
+        let mut diag = handler.struct_span_err_with_code(
             self.span,
             match self.reason {
                 UnsupportedLiteralReason::Generic => fluent::attr::unsupported_literal_generic,
@@ -223,8 +225,10 @@ impl<'a> SessionDiagnostic<'a> for UnsupportedLiteral {
             error_code!(E0565),
         );
         if self.is_bytestr {
+            let start_point = handler.span_start_point_from_emitter(self.span).unwrap_or(self.span);
+
             diag.span_suggestion(
-                sess.source_map().start_point(self.span),
+                start_point,
                 fluent::attr::unsupported_literal_suggestion,
                 "",
                 Applicability::MaybeIncorrect,

compiler/rustc_errors/src/lib.rs

@@ -1098,6 +1098,28 @@ impl Handler {
         );
         std::mem::take(&mut self.inner.borrow_mut().fulfilled_expectations)
     }
+
+    pub fn span_to_snippet_from_emitter(
+        &self,
+        span: rustc_span::Span,
+    ) -> Option<Result<String, rustc_span::SpanSnippetError>> {
+        self.inner
+            .borrow()
+            .emitter
+            .source_map()
+            .map_or_else(|| Option::None, |sm| Some(sm.span_to_snippet(span)))
+    }
+
+    pub fn span_start_point_from_emitter(
+        &self,
+        span: rustc_span::Span,
+    ) -> Option<rustc_span::Span> {
+        self.inner
+            .borrow()
+            .emitter
+            .source_map()
+            .map_or_else(|| Option::None, |sm| Some(sm.start_point(span)))
+    }
 }
 
 impl HandlerInner {

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -341,7 +341,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 multi_suggestions,
                 bad_label,
             }
-            .into_diagnostic(&self.tcx.sess.parse_sess),
+            .into_diagnostic(&self.tcx.sess.parse_sess.span_diagnostic),
             TypeAnnotationNeeded::E0283 => AmbigousImpl {
                 span,
                 source_kind,
@@ -351,7 +351,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 multi_suggestions,
                 bad_label,
             }
-            .into_diagnostic(&self.tcx.sess.parse_sess),
+            .into_diagnostic(&self.tcx.sess.parse_sess.span_diagnostic),
             TypeAnnotationNeeded::E0284 => AmbigousReturn {
                 span,
                 source_kind,
@@ -361,7 +361,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 multi_suggestions,
                 bad_label,
             }
-            .into_diagnostic(&self.tcx.sess.parse_sess),
+            .into_diagnostic(&self.tcx.sess.parse_sess.span_diagnostic),
         }
     }
 
@@ -537,7 +537,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 multi_suggestions,
                 bad_label: None,
             }
-            .into_diagnostic(&self.tcx.sess.parse_sess),
+            .into_diagnostic(&self.tcx.sess.parse_sess.span_diagnostic),
             TypeAnnotationNeeded::E0283 => AmbigousImpl {
                 span,
                 source_kind,
@@ -547,7 +547,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 multi_suggestions,
                 bad_label: None,
             }
-            .into_diagnostic(&self.tcx.sess.parse_sess),
+            .into_diagnostic(&self.tcx.sess.parse_sess.span_diagnostic),
             TypeAnnotationNeeded::E0284 => AmbigousReturn {
                 span,
                 source_kind,
@@ -557,7 +557,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 multi_suggestions,
                 bad_label: None,
             }
-            .into_diagnostic(&self.tcx.sess.parse_sess),
+            .into_diagnostic(&self.tcx.sess.parse_sess.span_diagnostic),
         }
     }
 
@@ -575,7 +575,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             span,
             generator_kind: GeneratorKindAsDiagArg(kind),
         }
-        .into_diagnostic(&self.tcx.sess.parse_sess)
+        .into_diagnostic(&self.tcx.sess.parse_sess.span_diagnostic)
     }
 }
 

compiler/rustc_lint/src/errors.rs

@@ -1,6 +1,6 @@
-use rustc_errors::{fluent, AddSubdiagnostic, ErrorGuaranteed};
+use rustc_errors::{fluent, AddSubdiagnostic, ErrorGuaranteed, Handler};
 use rustc_macros::{SessionDiagnostic, SessionSubdiagnostic};
-use rustc_session::{lint::Level, parse::ParseSess, SessionDiagnostic};
+use rustc_session::{lint::Level, SessionDiagnostic};
 use rustc_span::{Span, Symbol};
 
 #[derive(SessionDiagnostic)]
@@ -122,9 +122,9 @@ pub struct CheckNameUnknown {
 impl SessionDiagnostic<'_> for CheckNameUnknown {
     fn into_diagnostic(
         self,
-        sess: &ParseSess,
+        handler: &Handler,
     ) -> rustc_errors::DiagnosticBuilder<'_, ErrorGuaranteed> {
-        let mut diag = sess.struct_err(fluent::lint::check_name_unknown);
+        let mut diag = handler.struct_err(fluent::lint::check_name_unknown);
         diag.code(rustc_errors::error_code!(E0602));
         if let Some(suggestion) = self.suggestion {
             diag.help(fluent::lint::help);

compiler/rustc_macros/src/diagnostics/diagnostic.rs

@@ -88,7 +88,7 @@ impl<'a> SessionDiagnosticDerive<'a> {
             {
                 fn into_diagnostic(
                     self,
-                    #sess: &'__session_diagnostic_sess rustc_session::parse::ParseSess
+                    #sess: &'__session_diagnostic_sess rustc_errors::Handler
                 ) -> rustc_errors::DiagnosticBuilder<'__session_diagnostic_sess, G> {
                     use rustc_errors::IntoDiagnosticArg;
                     #implementation

compiler/rustc_metadata/src/errors.rs

@@ -424,9 +424,9 @@ pub(crate) struct MultipleCandidates {
 impl SessionDiagnostic<'_> for MultipleCandidates {
     fn into_diagnostic(
         self,
-        sess: &'_ rustc_session::parse::ParseSess,
+        handler: &'_ rustc_errors::Handler,
     ) -> rustc_errors::DiagnosticBuilder<'_, ErrorGuaranteed> {
-        let mut diag = sess.struct_err(rustc_errors::fluent::metadata::multiple_candidates);
+        let mut diag = handler.struct_err(rustc_errors::fluent::metadata::multiple_candidates);
         diag.set_arg("crate_name", self.crate_name);
         diag.set_arg("flavor", self.flavor);
         diag.code(error_code!(E0465));
@@ -540,9 +540,9 @@ pub struct InvalidMetadataFiles {
 impl SessionDiagnostic<'_> for InvalidMetadataFiles {
     fn into_diagnostic(
         self,
-        sess: &'_ rustc_session::parse::ParseSess,
+        handler: &'_ rustc_errors::Handler,
     ) -> rustc_errors::DiagnosticBuilder<'_, ErrorGuaranteed> {
-        let mut diag = sess.struct_err(rustc_errors::fluent::metadata::invalid_meta_files);
+        let mut diag = handler.struct_err(rustc_errors::fluent::metadata::invalid_meta_files);
         diag.set_arg("crate_name", self.crate_name);
         diag.set_arg("add_info", self.add_info);
         diag.code(error_code!(E0786));
@@ -568,9 +568,9 @@ pub struct CannotFindCrate {
 impl SessionDiagnostic<'_> for CannotFindCrate {
     fn into_diagnostic(
         self,
-        sess: &'_ rustc_session::parse::ParseSess,
+        handler: &'_ rustc_errors::Handler,
     ) -> rustc_errors::DiagnosticBuilder<'_, ErrorGuaranteed> {
-        let mut diag = sess.struct_err(rustc_errors::fluent::metadata::cannot_find_crate);
+        let mut diag = handler.struct_err(rustc_errors::fluent::metadata::cannot_find_crate);
         diag.set_arg("crate_name", self.crate_name);
         diag.set_arg("add_info", self.add_info);
         diag.set_arg("locator_triple", self.locator_triple.triple());

compiler/rustc_monomorphize/src/errors.rs

@@ -47,9 +47,10 @@ pub struct UnusedGenericParams {
 impl SessionDiagnostic<'_> for UnusedGenericParams {
     fn into_diagnostic(
         self,
-        sess: &'_ rustc_session::parse::ParseSess,
+        handler: &'_ rustc_errors::Handler,
     ) -> rustc_errors::DiagnosticBuilder<'_, ErrorGuaranteed> {
-        let mut diag = sess.struct_err(rustc_errors::fluent::monomorphize::unused_generic_params);
+        let mut diag =
+            handler.struct_err(rustc_errors::fluent::monomorphize::unused_generic_params);
         diag.set_span(self.span);
         for (span, name) in self.param_spans.into_iter().zip(self.param_names) {
             // FIXME: I can figure out how to do a label with a fluent string with a fixed message,

compiler/rustc_parse/src/parser/expr.rs

@@ -1997,7 +1997,7 @@ impl<'a> Parser<'a> {
                     return Err(MissingSemicolonBeforeArray {
                         open_delim: open_delim_span,
                         semicolon: prev_span.shrink_to_hi(),
-                    }.into_diagnostic(self.sess));
+                    }.into_diagnostic(&self.sess.span_diagnostic));
                 }
                 Ok(_) => (),
                 Err(err) => err.cancel(),
@@ -2745,7 +2745,8 @@ impl<'a> Parser<'a> {
     fn parse_try_block(&mut self, span_lo: Span) -> PResult<'a, P<Expr>> {
         let (attrs, body) = self.parse_inner_attrs_and_block()?;
         if self.eat_keyword(kw::Catch) {
-            Err(CatchAfterTry { span: self.prev_token.span }.into_diagnostic(self.sess))
+            Err(CatchAfterTry { span: self.prev_token.span }
+                .into_diagnostic(&self.sess.span_diagnostic))
         } else {
             let span = span_lo.to(body.span);
             self.sess.gated_spans.gate(sym::try_blocks, span);

compiler/rustc_query_system/src/query/job.rs

@@ -572,7 +572,7 @@ pub(crate) fn report_cycle<'a>(
         stack_count,
     };
 
-    cycle_diag.into_diagnostic(&sess.parse_sess)
+    cycle_diag.into_diagnostic(&sess.parse_sess.span_diagnostic)
 }
 
 pub fn print_query_stack<CTX: QueryContext>(

compiler/rustc_session/src/parse.rs

@@ -343,7 +343,7 @@ impl ParseSess {
         &'a self,
         err: impl SessionDiagnostic<'a>,
     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
-        err.into_diagnostic(self)
+        err.into_diagnostic(&self.span_diagnostic)
     }
 
     pub fn emit_err<'a>(&'a self, err: impl SessionDiagnostic<'a>) -> ErrorGuaranteed {
@@ -354,7 +354,7 @@ impl ParseSess {
         &'a self,
         warning: impl SessionDiagnostic<'a, ()>,
     ) -> DiagnosticBuilder<'a, ()> {
-        warning.into_diagnostic(self)
+        warning.into_diagnostic(&self.span_diagnostic)
     }
 
     pub fn emit_warning<'a>(&'a self, warning: impl SessionDiagnostic<'a, ()>) {
@@ -365,7 +365,7 @@ impl ParseSess {
         &'a self,
         fatal: impl SessionDiagnostic<'a, !>,
     ) -> DiagnosticBuilder<'a, !> {
-        fatal.into_diagnostic(self)
+        fatal.into_diagnostic(&self.span_diagnostic)
     }
 
     pub fn emit_fatal<'a>(&'a self, fatal: impl SessionDiagnostic<'a, !>) -> ! {

compiler/rustc_session/src/session.rs

@@ -21,7 +21,7 @@ use rustc_errors::json::JsonEmitter;
 use rustc_errors::registry::Registry;
 use rustc_errors::{
     error_code, fallback_fluent_bundle, DiagnosticBuilder, DiagnosticId, DiagnosticMessage,
-    EmissionGuarantee, ErrorGuaranteed, FluentBundle, LazyFallbackBundle, MultiSpan,
+    EmissionGuarantee, ErrorGuaranteed, FluentBundle, Handler, LazyFallbackBundle, MultiSpan,
 };
 use rustc_macros::HashStable_Generic;
 pub use rustc_span::def_id::StableCrateId;
@@ -220,9 +220,9 @@ pub struct PerfStats {
 /// `#[derive(SessionDiagnostic)]` -- see [rustc_macros::SessionDiagnostic].
 #[rustc_diagnostic_item = "SessionDiagnostic"]
 pub trait SessionDiagnostic<'a, T: EmissionGuarantee = ErrorGuaranteed> {
-    /// Write out as a diagnostic out of `sess`.
+    /// Write out as a diagnostic out of `Handler`.
     #[must_use]
-    fn into_diagnostic(self, sess: &'a ParseSess) -> DiagnosticBuilder<'a, T>;
+    fn into_diagnostic(self, handler: &'a Handler) -> DiagnosticBuilder<'a, T>;
 }
 
 impl Session {

compiler/rustc_trait_selection/src/errors.rs

@@ -1,7 +1,7 @@
-use rustc_errors::{fluent, ErrorGuaranteed};
+use rustc_errors::{fluent, ErrorGuaranteed, Handler};
 use rustc_macros::SessionDiagnostic;
 use rustc_middle::ty::{PolyTraitRef, Ty, Unevaluated};
-use rustc_session::{parse::ParseSess, Limit, SessionDiagnostic};
+use rustc_session::{Limit, SessionDiagnostic};
 use rustc_span::{Span, Symbol};
 
 #[derive(SessionDiagnostic)]
@@ -69,9 +69,9 @@ pub struct NegativePositiveConflict<'a> {
 impl SessionDiagnostic<'_> for NegativePositiveConflict<'_> {
     fn into_diagnostic(
         self,
-        sess: &ParseSess,
+        handler: &Handler,
     ) -> rustc_errors::DiagnosticBuilder<'_, ErrorGuaranteed> {
-        let mut diag = sess.struct_err(fluent::trait_selection::negative_positive_conflict);
+        let mut diag = handler.struct_err(fluent::trait_selection::negative_positive_conflict);
         diag.set_arg("trait_desc", self.trait_desc);
         diag.set_arg(
             "self_desc",

compiler/rustc_typeck/src/errors.rs

@@ -1,8 +1,8 @@
 //! Errors emitted by typeck.
-use rustc_errors::{error_code, Applicability, DiagnosticBuilder, ErrorGuaranteed};
+use rustc_errors::{error_code, Applicability, DiagnosticBuilder, ErrorGuaranteed, Handler};
 use rustc_macros::{LintDiagnostic, SessionDiagnostic, SessionSubdiagnostic};
 use rustc_middle::ty::Ty;
-use rustc_session::{parse::ParseSess, SessionDiagnostic};
+use rustc_session::SessionDiagnostic;
 use rustc_span::{symbol::Ident, Span, Symbol};
 
 #[derive(SessionDiagnostic)]
@@ -250,8 +250,8 @@ pub struct MissingTypeParams {
 
 // Manual implementation of `SessionDiagnostic` to be able to call `span_to_snippet`.
 impl<'a> SessionDiagnostic<'a> for MissingTypeParams {
-    fn into_diagnostic(self, sess: &'a ParseSess) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+    fn into_diagnostic(self, handler: &'a Handler) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
-        let mut err = sess.span_diagnostic.struct_span_err_with_code(
+        let mut err = handler.struct_span_err_with_code(
             self.span,
             rustc_errors::fluent::typeck::missing_type_params,
             error_code!(E0393),
@@ -269,8 +269,8 @@ impl<'a> SessionDiagnostic<'a> for MissingTypeParams {
         err.span_label(self.def_span, rustc_errors::fluent::typeck::label);
 
         let mut suggested = false;
-        if let (Ok(snippet), true) = (
+        if let (Some(Ok(snippet)), true) = (
-            sess.source_map().span_to_snippet(self.span),
+            handler.span_to_snippet_from_emitter(self.span),
             // Don't suggest setting the type params if there are some already: the order is
             // tricky to get right and the user will already know what the syntax is.
             self.empty_generic_args,

src/test/ui-fulldeps/internal-lints/diagnostics.rs

@@ -11,9 +11,9 @@ extern crate rustc_macros;
 extern crate rustc_session;
 extern crate rustc_span;
 
-use rustc_errors::{AddSubdiagnostic, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, fluent};
+use rustc_errors::{AddSubdiagnostic, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, Handler, fluent};
 use rustc_macros::{SessionDiagnostic, SessionSubdiagnostic};
-use rustc_session::{parse::ParseSess, SessionDiagnostic};
+use rustc_session::SessionDiagnostic;
 use rustc_span::Span;
 
 #[derive(SessionDiagnostic)]
@@ -33,8 +33,8 @@ struct Note {
 pub struct UntranslatableInSessionDiagnostic;
 
 impl<'a> SessionDiagnostic<'a, ErrorGuaranteed> for UntranslatableInSessionDiagnostic {
-    fn into_diagnostic(self, sess: &'a ParseSess) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+    fn into_diagnostic(self, handler: &'a Handler) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
-        sess.struct_err("untranslatable diagnostic")
+        handler.struct_err("untranslatable diagnostic")
         //~^ ERROR diagnostics should be created using translatable messages
     }
 }
@@ -42,8 +42,8 @@ impl<'a> SessionDiagnostic<'a, ErrorGuaranteed> for UntranslatableInSessionDiagn
 pub struct TranslatableInSessionDiagnostic;
 
 impl<'a> SessionDiagnostic<'a, ErrorGuaranteed> for TranslatableInSessionDiagnostic {
-    fn into_diagnostic(self, sess: &'a ParseSess) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+    fn into_diagnostic(self, handler: &'a Handler) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
-        sess.struct_err(fluent::parser::expect_path)
+        handler.struct_err(fluent::parser::expect_path)
     }
 }
 
@@ -64,11 +64,11 @@ impl AddSubdiagnostic for TranslatableInAddSubdiagnostic {
     }
 }
 
-pub fn make_diagnostics<'a>(sess: &'a ParseSess) {
+pub fn make_diagnostics<'a>(handler: &'a Handler) {
-    let _diag = sess.struct_err(fluent::parser::expect_path);
+    let _diag = handler.struct_err(fluent::parser::expect_path);
     //~^ ERROR diagnostics should only be created in `SessionDiagnostic`/`AddSubdiagnostic` impls
 
-    let _diag = sess.struct_err("untranslatable diagnostic");
+    let _diag = handler.struct_err("untranslatable diagnostic");
     //~^ ERROR diagnostics should only be created in `SessionDiagnostic`/`AddSubdiagnostic` impls
     //~^^ ERROR diagnostics should be created using translatable messages
 }
@@ -76,6 +76,6 @@ pub fn make_diagnostics<'a>(sess: &'a ParseSess) {
 // Check that `rustc_lint_diagnostics`-annotated functions aren't themselves linted.
 
 #[rustc_lint_diagnostics]
-pub fn skipped_because_of_annotation<'a>(sess: &'a ParseSess) {
+pub fn skipped_because_of_annotation<'a>(handler: &'a Handler) {
-    let _diag = sess.struct_err("untranslatable diagnostic"); // okay!
+    let _diag = handler.struct_err("untranslatable diagnostic"); // okay!
 }