migrate: UnknownTool error to SessionDiagnostic

compiler/rustc_error_messages/locales/en-US/lint.ftl

@@ -393,3 +393,6 @@ lint_builtin_deref_nullptr = dereferencing a null pointer
     .label = this code causes undefined behavior when executed
 
 lint_builtin_asm_labels = avoid using named labels in inline assembly
+
+lint_unknown_tool = unknown tool name `{$tool_name}` found in scoped lint: `{$tool_name}::{$lint_name}`
+    .help = add `#![register_tool({$tool_name})]` to the crate root

compiler/rustc_lint/src/errors.rs

@@ -0,0 +1,13 @@
+use rustc_macros::SessionDiagnostic;
+use rustc_span::Span;
+
+#[derive(SessionDiagnostic)]
+#[error(lint::unknown_tool, code = "E0710")]
+pub struct UnknownTool {
+    #[primary_span]
+    pub span: Option<Span>,
+    pub tool_name: String,
+    pub lint_name: String,
+    #[help]
+    pub is_nightly_build: Option<()>,
+}

compiler/rustc_lint/src/levels.rs

@@ -1,3 +1,6 @@
+// #![deny(rustc::diagnostic_outside_of_impl)]
+// #![deny(rustc::untranslatable_diagnostic)]
+//
 use crate::context::{CheckLintNameResult, LintStore};
 use crate::late::unerased_lint_store;
 use rustc_ast as ast;
@@ -23,6 +26,8 @@
 use rustc_span::{Span, DUMMY_SP};
 use tracing::debug;
 
+use crate::errors::UnknownTool;
+
 fn lint_levels(tcx: TyCtxt<'_>, (): ()) -> LintLevelMap {
     let store = unerased_lint_store(tcx);
     let levels =
@@ -485,22 +490,12 @@ pub(crate) fn push(
                     }
 
                     &CheckLintNameResult::NoTool => {
-                        let mut err = struct_span_err!(
-                            sess,
-                            tool_ident.map_or(DUMMY_SP, |ident| ident.span),
-                            E0710,
-                            "unknown tool name `{}` found in scoped lint: `{}::{}`",
-                            tool_name.unwrap(),
-                            tool_name.unwrap(),
-                            pprust::path_to_string(&meta_item.path),
-                        );
-                        if sess.is_nightly_build() {
-                            err.help(&format!(
-                                "add `#![register_tool({})]` to the crate root",
-                                tool_name.unwrap()
-                            ));
-                        }
-                        err.emit();
+                        sess.emit_err(UnknownTool {
+                            span: tool_ident.map(|ident| ident.span),
+                            tool_name: tool_name.unwrap().to_string(),
+                            lint_name: pprust::path_to_string(&meta_item.path),
+                            is_nightly_build: sess.is_nightly_build().then_some(()),
+                        });
                         continue;
                     }
 

compiler/rustc_lint/src/lib.rs

@@ -36,6 +36,8 @@
 #![feature(let_else)]
 #![feature(never_type)]
 #![recursion_limit = "256"]
+// #![deny(rustc::diagnostic_outside_of_impl)]
+// #![deny(rustc::untranslatable_diagnostic)]
 
 #[macro_use]
 extern crate rustc_middle;
@@ -47,6 +49,7 @@
 mod context;
 mod early;
 mod enum_intrinsics_non_enums;
+mod errors;
 mod expect;
 pub mod hidden_unicode_codepoints;
 mod internal;