Remove `LintDiagnostic::msg`

* instead simply set the primary message inside the lint decorator functions
* it used to be this way before [#]101986 which introduced `msg` to prevent
  good path delayed bugs (which no longer exist) from firing under certain
  circumstances when lints were suppressed / silenced
* this is no longer necessary for various reasons I presume
* it shaves off complexity and makes further changes easier to implement

5 files changed, 43 insertions, 94 deletions

diff --git a/compiler/rustc_lint/src/context.rs b/compiler/rustc_lint/src/context.rs
index deeb3ae090c..34b84658dc0 100644
--- a/compiler/rustc_lint/src/context.rs
+++ b/compiler/rustc_lint/src/context.rs
@@ -21,7 +21,7 @@ use crate::passes::{EarlyLintPassObject, LateLintPassObject};
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::sync;
 use rustc_data_structures::unord::UnordMap;
-use rustc_errors::{Diag, DiagMessage, LintDiagnostic, MultiSpan};
+use rustc_errors::{Diag, LintDiagnostic, MultiSpan};
 use rustc_feature::Features;
 use rustc_hir as hir;
 use rustc_hir::def::Res;
@@ -556,7 +556,6 @@ pub trait LintContext {
         &self,
         lint: &'static Lint,
         span: Option<S>,
-        msg: impl Into<DiagMessage>,
         decorate: impl for<'a, 'b> FnOnce(&'b mut Diag<'a, ()>),
     );
 
@@ -568,8 +567,8 @@ pub trait LintContext {
         span: S,
         decorator: impl for<'a> LintDiagnostic<'a, ()>,
     ) {
-        self.opt_span_lint(lint, Some(span), decorator.msg(), |diag| {
-            decorator.decorate_lint(diag);
+        self.opt_span_lint(lint, Some(span), |lint| {
+            decorator.decorate_lint(lint);
         });
     }
 
@@ -581,17 +580,16 @@ pub trait LintContext {
         &self,
         lint: &'static Lint,
         span: S,
-        msg: impl Into<DiagMessage>,
         decorate: impl for<'a, 'b> FnOnce(&'b mut Diag<'a, ()>),
     ) {
-        self.opt_span_lint(lint, Some(span), msg, decorate);
+        self.opt_span_lint(lint, Some(span), decorate);
     }
 
     /// Emit a lint from a lint struct (some type that implements `LintDiagnostic`, typically
     /// generated by `#[derive(LintDiagnostic)]`).
     fn emit_lint(&self, lint: &'static Lint, decorator: impl for<'a> LintDiagnostic<'a, ()>) {
-        self.opt_span_lint(lint, None as Option<Span>, decorator.msg(), |diag| {
-            decorator.decorate_lint(diag);
+        self.opt_span_lint(lint, None as Option<Span>, |lint| {
+            decorator.decorate_lint(lint);
         });
     }
 
@@ -599,13 +597,8 @@ pub trait LintContext {
     ///
     /// [`lint_level`]: rustc_middle::lint::lint_level#decorate-signature
     #[rustc_lint_diagnostics]
-    fn lint(
-        &self,
-        lint: &'static Lint,
-        msg: impl Into<DiagMessage>,
-        decorate: impl for<'a, 'b> FnOnce(&'b mut Diag<'a, ()>),
-    ) {
-        self.opt_span_lint(lint, None as Option<Span>, msg, decorate);
+    fn lint(&self, lint: &'static Lint, decorate: impl for<'a, 'b> FnOnce(&'b mut Diag<'a, ()>)) {
+        self.opt_span_lint(lint, None as Option<Span>, decorate);
     }
 
     /// This returns the lint level for the given lint at the current location.
@@ -668,14 +661,13 @@ impl<'tcx> LintContext for LateContext<'tcx> {
         &self,
         lint: &'static Lint,
         span: Option<S>,
-        msg: impl Into<DiagMessage>,
         decorate: impl for<'a, 'b> FnOnce(&'b mut Diag<'a, ()>),
     ) {
         let hir_id = self.last_node_with_lint_attrs;
 
         match span {
-            Some(s) => self.tcx.node_span_lint(lint, hir_id, s, msg, decorate),
-            None => self.tcx.node_lint(lint, hir_id, msg, decorate),
+            Some(s) => self.tcx.node_span_lint(lint, hir_id, s, decorate),
+            None => self.tcx.node_lint(lint, hir_id, decorate),
         }
     }
 
@@ -695,10 +687,9 @@ impl LintContext for EarlyContext<'_> {
         &self,
         lint: &'static Lint,
         span: Option<S>,
-        msg: impl Into<DiagMessage>,
         decorate: impl for<'a, 'b> FnOnce(&'b mut Diag<'a, ()>),
     ) {
-        self.builder.opt_span_lint(lint, span.map(|s| s.into()), msg, decorate)
+        self.builder.opt_span_lint(lint, span.map(|s| s.into()), decorate)
     }
 
     fn get_lint_level(&self, lint: &'static Lint) -> Level {
diff --git a/compiler/rustc_lint/src/impl_trait_overcaptures.rs b/compiler/rustc_lint/src/impl_trait_overcaptures.rs
index 30bf80b915b..ca3e1ee06d9 100644
--- a/compiler/rustc_lint/src/impl_trait_overcaptures.rs
+++ b/compiler/rustc_lint/src/impl_trait_overcaptures.rs
@@ -369,6 +369,7 @@ struct ImplTraitOvercapturesLint<'tcx> {
 
 impl<'a> LintDiagnostic<'a, ()> for ImplTraitOvercapturesLint<'_> {
     fn decorate_lint<'b>(self, diag: &'b mut rustc_errors::Diag<'a, ()>) {
+        diag.primary_message(fluent::lint_impl_trait_overcaptures);
         diag.arg("self_ty", self.self_ty.to_string())
             .arg("num_captured", self.num_captured)
             .span_note(self.uncaptured_spans, fluent::lint_note)
@@ -382,10 +383,6 @@ impl<'a> LintDiagnostic<'a, ()> for ImplTraitOvercapturesLint<'_> {
             );
         }
     }
-
-    fn msg(&self) -> rustc_errors::DiagMessage {
-        fluent::lint_impl_trait_overcaptures
-    }
 }
 
 #[derive(LintDiagnostic)]
diff --git a/compiler/rustc_lint/src/levels.rs b/compiler/rustc_lint/src/levels.rs
index 12b3d1d2f9e..5d065686546 100644
--- a/compiler/rustc_lint/src/levels.rs
+++ b/compiler/rustc_lint/src/levels.rs
@@ -16,7 +16,7 @@ use crate::{
 use rustc_ast as ast;
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::FxIndexMap;
-use rustc_errors::{Diag, DiagMessage, LintDiagnostic, MultiSpan};
+use rustc_errors::{Diag, LintDiagnostic, MultiSpan};
 use rustc_feature::{Features, GateIssue};
 use rustc_hir as hir;
 use rustc_hir::intravisit::{self, Visitor};
@@ -1063,26 +1063,19 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
             // FIXME: make this translatable
             #[allow(rustc::diagnostic_outside_of_impl)]
             #[allow(rustc::untranslatable_diagnostic)]
-            lint_level(
-                self.sess,
-                lint,
-                level,
-                src,
-                Some(span.into()),
-                fluent::lint_unknown_gated_lint,
-                |lint| {
-                    lint.arg("name", lint_id.lint.name_lower());
-                    lint.note(fluent::lint_note);
-                    rustc_session::parse::add_feature_diagnostics_for_issue(
-                        lint,
-                        &self.sess,
-                        feature,
-                        GateIssue::Language,
-                        lint_from_cli,
-                        None,
-                    );
-                },
-            );
+            lint_level(self.sess, lint, level, src, Some(span.into()), |lint| {
+                lint.primary_message(fluent::lint_unknown_gated_lint);
+                lint.arg("name", lint_id.lint.name_lower());
+                lint.note(fluent::lint_note);
+                rustc_session::parse::add_feature_diagnostics_for_issue(
+                    lint,
+                    &self.sess,
+                    feature,
+                    GateIssue::Language,
+                    lint_from_cli,
+                    None,
+                );
+            });
         }
 
         false
@@ -1103,11 +1096,10 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
         &self,
         lint: &'static Lint,
         span: Option<MultiSpan>,
-        msg: impl Into<DiagMessage>,
         decorate: impl for<'a, 'b> FnOnce(&'b mut Diag<'a, ()>),
     ) {
         let (level, src) = self.lint_level(lint);
-        lint_level(self.sess, lint, level, src, span, msg, decorate)
+        lint_level(self.sess, lint, level, src, span, decorate)
     }
 
     #[track_caller]
@@ -1118,7 +1110,7 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
         decorate: impl for<'a> LintDiagnostic<'a, ()>,
     ) {
         let (level, src) = self.lint_level(lint);
-        lint_level(self.sess, lint, level, src, Some(span), decorate.msg(), |lint| {
+        lint_level(self.sess, lint, level, src, Some(span), |lint| {
             decorate.decorate_lint(lint);
         });
     }
@@ -1126,7 +1118,7 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
     #[track_caller]
     pub fn emit_lint(&self, lint: &'static Lint, decorate: impl for<'a> LintDiagnostic<'a, ()>) {
         let (level, src) = self.lint_level(lint);
-        lint_level(self.sess, lint, level, src, None, decorate.msg(), |lint| {
+        lint_level(self.sess, lint, level, src, None, |lint| {
             decorate.decorate_lint(lint);
         });
     }
diff --git a/compiler/rustc_lint/src/lints.rs b/compiler/rustc_lint/src/lints.rs
index 3bd6faca379..4b1626ca556 100644
--- a/compiler/rustc_lint/src/lints.rs
+++ b/compiler/rustc_lint/src/lints.rs
@@ -145,12 +145,9 @@ pub struct BuiltinMissingDebugImpl<'a> {
 // Needed for def_path_str
 impl<'a> LintDiagnostic<'a, ()> for BuiltinMissingDebugImpl<'_> {
     fn decorate_lint<'b>(self, diag: &'b mut rustc_errors::Diag<'a, ()>) {
+        diag.primary_message(fluent::lint_builtin_missing_debug_impl);
         diag.arg("debug", self.tcx.def_path_str(self.def_id));
     }
-
-    fn msg(&self) -> DiagMessage {
-        fluent::lint_builtin_missing_debug_impl
-    }
 }
 
 #[derive(LintDiagnostic)]
@@ -250,6 +247,7 @@ pub struct BuiltinUngatedAsyncFnTrackCaller<'a> {
 
 impl<'a> LintDiagnostic<'a, ()> for BuiltinUngatedAsyncFnTrackCaller<'_> {
     fn decorate_lint<'b>(self, diag: &'b mut Diag<'a, ()>) {
+        diag.primary_message(fluent::lint_ungated_async_fn_track_caller);
         diag.span_label(self.label, fluent::lint_label);
         rustc_session::parse::add_feature_diagnostics(
             diag,
@@ -257,10 +255,6 @@ impl<'a> LintDiagnostic<'a, ()> for BuiltinUngatedAsyncFnTrackCaller<'_> {
             sym::async_fn_track_caller,
         );
     }
-
-    fn msg(&self) -> DiagMessage {
-        fluent::lint_ungated_async_fn_track_caller
-    }
 }
 
 #[derive(LintDiagnostic)]
@@ -432,6 +426,7 @@ pub struct BuiltinUnpermittedTypeInit<'a> {
 
 impl<'a> LintDiagnostic<'a, ()> for BuiltinUnpermittedTypeInit<'_> {
     fn decorate_lint<'b>(self, diag: &'b mut Diag<'a, ()>) {
+        diag.primary_message(self.msg);
         diag.arg("ty", self.ty);
         diag.span_label(self.label, fluent::lint_builtin_unpermitted_type_init_label);
         if let InhabitedPredicate::True = self.ty.inhabited_predicate(self.tcx) {
@@ -443,10 +438,6 @@ impl<'a> LintDiagnostic<'a, ()> for BuiltinUnpermittedTypeInit<'_> {
         }
         self.sub.add_to_diag(diag);
     }
-
-    fn msg(&self) -> DiagMessage {
-        self.msg.clone()
-    }
 }
 
 // FIXME(davidtwco): make translatable
@@ -1168,6 +1159,7 @@ pub struct NonFmtPanicUnused {
 // Used because of two suggestions based on one Option<Span>
 impl<'a> LintDiagnostic<'a, ()> for NonFmtPanicUnused {
     fn decorate_lint<'b>(self, diag: &'b mut Diag<'a, ()>) {
+        diag.primary_message(fluent::lint_non_fmt_panic_unused);
         diag.arg("count", self.count);
         diag.note(fluent::lint_note);
         if let Some(span) = self.suggestion {
@@ -1185,10 +1177,6 @@ impl<'a> LintDiagnostic<'a, ()> for NonFmtPanicUnused {
             );
         }
     }
-
-    fn msg(&self) -> DiagMessage {
-        fluent::lint_non_fmt_panic_unused
-    }
 }
 
 #[derive(LintDiagnostic)]
@@ -1410,13 +1398,10 @@ pub struct DropTraitConstraintsDiag<'a> {
 // Needed for def_path_str
 impl<'a> LintDiagnostic<'a, ()> for DropTraitConstraintsDiag<'_> {
     fn decorate_lint<'b>(self, diag: &'b mut Diag<'a, ()>) {
+        diag.primary_message(fluent::lint_drop_trait_constraints);
         diag.arg("predicate", self.predicate);
         diag.arg("needs_drop", self.tcx.def_path_str(self.def_id));
     }
-
-    fn msg(&self) -> DiagMessage {
-        fluent::lint_drop_trait_constraints
-    }
 }
 
 pub struct DropGlue<'a> {
@@ -1427,12 +1412,9 @@ pub struct DropGlue<'a> {
 // Needed for def_path_str
 impl<'a> LintDiagnostic<'a, ()> for DropGlue<'_> {
     fn decorate_lint<'b>(self, diag: &'b mut Diag<'a, ()>) {
+        diag.primary_message(fluent::lint_drop_glue);
         diag.arg("needs_drop", self.tcx.def_path_str(self.def_id));
     }
-
-    fn msg(&self) -> DiagMessage {
-        fluent::lint_drop_glue
-    }
 }
 
 // types.rs
@@ -1710,6 +1692,7 @@ pub struct ImproperCTypes<'a> {
 // Used because of the complexity of Option<DiagMessage>, DiagMessage, and Option<Span>
 impl<'a> LintDiagnostic<'a, ()> for ImproperCTypes<'_> {
     fn decorate_lint<'b>(self, diag: &'b mut Diag<'a, ()>) {
+        diag.primary_message(fluent::lint_improper_ctypes);
         diag.arg("ty", self.ty);
         diag.arg("desc", self.desc);
         diag.span_label(self.label, fluent::lint_label);
@@ -1721,10 +1704,6 @@ impl<'a> LintDiagnostic<'a, ()> for ImproperCTypes<'_> {
             diag.span_note(note, fluent::lint_note);
         }
     }
-
-    fn msg(&self) -> DiagMessage {
-        fluent::lint_improper_ctypes
-    }
 }
 
 #[derive(LintDiagnostic)]
@@ -1853,6 +1832,7 @@ pub enum UnusedDefSuggestion {
 // Needed because of def_path_str
 impl<'a> LintDiagnostic<'a, ()> for UnusedDef<'_, '_> {
     fn decorate_lint<'b>(self, diag: &'b mut Diag<'a, ()>) {
+        diag.primary_message(fluent::lint_unused_def);
         diag.arg("pre", self.pre);
         diag.arg("post", self.post);
         diag.arg("def", self.cx.tcx.def_path_str(self.def_id));
@@ -1864,10 +1844,6 @@ impl<'a> LintDiagnostic<'a, ()> for UnusedDef<'_, '_> {
             diag.subdiagnostic(diag.dcx, sugg);
         }
     }
-
-    fn msg(&self) -> DiagMessage {
-        fluent::lint_unused_def
-    }
 }
 
 #[derive(LintDiagnostic)]
@@ -1936,15 +1912,12 @@ pub struct AsyncFnInTraitDiag {
 
 impl<'a> LintDiagnostic<'a, ()> for AsyncFnInTraitDiag {
     fn decorate_lint<'b>(self, diag: &'b mut Diag<'a, ()>) {
+        diag.primary_message(fluent::lint_async_fn_in_trait);
         diag.note(fluent::lint_note);
         if let Some(sugg) = self.sugg {
             diag.multipart_suggestion(fluent::lint_suggestion, sugg, Applicability::MaybeIncorrect);
         }
     }
-
-    fn msg(&self) -> DiagMessage {
-        fluent::lint_async_fn_in_trait
-    }
 }
 
 #[derive(LintDiagnostic)]
@@ -2260,10 +2233,8 @@ pub struct UnstableFeature {
 }
 
 impl<'a> LintDiagnostic<'a, ()> for UnstableFeature {
-    fn decorate_lint<'b>(self, _diag: &'b mut Diag<'a, ()>) {}
-
-    fn msg(&self) -> DiagMessage {
-        self.msg.clone()
+    fn decorate_lint<'b>(self, diag: &'b mut Diag<'a, ()>) {
+        diag.primary_message(self.msg);
     }
 }
 
@@ -2725,12 +2696,9 @@ pub struct AmbiguousGlobImports {
 
 impl<'a, G: EmissionGuarantee> LintDiagnostic<'a, G> for AmbiguousGlobImports {
     fn decorate_lint<'b>(self, diag: &'b mut Diag<'a, G>) {
+        diag.primary_message(self.ambiguity.msg.clone());
         rustc_errors::report_ambiguity_error(diag, self.ambiguity);
     }
-
-    fn msg(&self) -> DiagMessage {
-        DiagMessage::Str(self.ambiguity.msg.clone().into())
-    }
 }
 
 #[derive(LintDiagnostic)]
diff --git a/compiler/rustc_lint/src/non_fmt_panic.rs b/compiler/rustc_lint/src/non_fmt_panic.rs
index a6057afcbd6..c9d67854112 100644
--- a/compiler/rustc_lint/src/non_fmt_panic.rs
+++ b/compiler/rustc_lint/src/non_fmt_panic.rs
@@ -123,7 +123,8 @@ fn check_panic<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>, arg: &'tc
     }
 
     #[allow(rustc::diagnostic_outside_of_impl)]
-    cx.span_lint(NON_FMT_PANICS, arg_span, fluent::lint_non_fmt_panic, |lint| {
+    cx.span_lint(NON_FMT_PANICS, arg_span, |lint| {
+        lint.primary_message(fluent::lint_non_fmt_panic);
         lint.arg("name", symbol);
         lint.note(fluent::lint_note);
         lint.note(fluent::lint_more_info_note);