Auto merge of #125410 - fmease:adj-lint-diag-api, r=nnethercote

[perf] Delay the construction of early lint diag structs

Attacks some of the perf regressions from https://github.com/rust-lang/rust/pull/124417#issuecomment-2123700666.

See individual commits for details. The first three commits are not strictly necessary.
However, the 2nd one (06bc4fc67145e3a7be9b5a2cf2b5968cef36e587, *Remove `LintDiagnostic::msg`*) makes the main change way nicer to implement.
It's also pretty sweet on its own if I may say so myself.

5 files changed, 21 insertions, 34 deletions

diff --git a/compiler/rustc_middle/src/lint.rs b/compiler/rustc_middle/src/lint.rs
index d82d23d62af..4e655ca2027 100644
--- a/compiler/rustc_middle/src/lint.rs
+++ b/compiler/rustc_middle/src/lint.rs
@@ -2,7 +2,7 @@ use std::cmp;
 
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::sorted_map::SortedMap;
-use rustc_errors::{Diag, DiagMessage, MultiSpan};
+use rustc_errors::{Diag, MultiSpan};
 use rustc_hir::{HirId, ItemLocalId};
 use rustc_macros::HashStable;
 use rustc_session::lint::{
@@ -270,7 +270,6 @@ pub fn lint_level(
     level: Level,
     src: LintLevelSource,
     span: Option<MultiSpan>,
-    msg: impl Into<DiagMessage>,
     decorate: impl for<'a, 'b> FnOnce(&'b mut Diag<'a, ()>),
 ) {
     // Avoid codegen bloat from monomorphization by immediately doing dyn dispatch of `decorate` to
@@ -282,7 +281,6 @@ pub fn lint_level(
         level: Level,
         src: LintLevelSource,
         span: Option<MultiSpan>,
-        msg: impl Into<DiagMessage>,
         decorate: Box<dyn '_ + for<'a, 'b> FnOnce(&'b mut Diag<'a, ()>)>,
     ) {
         // Check for future incompatibility lints and issue a stronger warning.
@@ -351,10 +349,6 @@ pub fn lint_level(
             }
         }
 
-        // Delay evaluating and setting the primary message until after we've
-        // suppressed the lint due to macros.
-        err.primary_message(msg);
-
         err.is_lint(lint.name_lower(), has_future_breakage);
 
         // Lint diagnostics that are covered by the expect level will not be emitted outside
@@ -419,7 +413,7 @@ pub fn lint_level(
         explain_lint_level_source(lint, level, src, &mut err);
         err.emit()
     }
-    lint_level_impl(sess, lint, level, src, span, msg, Box::new(decorate))
+    lint_level_impl(sess, lint, level, src, span, Box::new(decorate))
 }
 
 /// Returns whether `span` originates in a foreign crate's external macro.
diff --git a/compiler/rustc_middle/src/middle/stability.rs b/compiler/rustc_middle/src/middle/stability.rs
index a377e35b2e9..8cf1bedf0da 100644
--- a/compiler/rustc_middle/src/middle/stability.rs
+++ b/compiler/rustc_middle/src/middle/stability.rs
@@ -157,6 +157,13 @@ pub struct Deprecated {
 
 impl<'a, G: EmissionGuarantee> rustc_errors::LintDiagnostic<'a, G> for Deprecated {
     fn decorate_lint<'b>(self, diag: &'b mut Diag<'a, G>) {
+        diag.primary_message(match &self.since_kind {
+            DeprecatedSinceKind::InEffect => crate::fluent_generated::middle_deprecated,
+            DeprecatedSinceKind::InFuture => crate::fluent_generated::middle_deprecated_in_future,
+            DeprecatedSinceKind::InVersion(_) => {
+                crate::fluent_generated::middle_deprecated_in_version
+            }
+        });
         diag.arg("kind", self.kind);
         diag.arg("path", self.path);
         if let DeprecatedSinceKind::InVersion(version) = self.since_kind {
@@ -172,16 +179,6 @@ impl<'a, G: EmissionGuarantee> rustc_errors::LintDiagnostic<'a, G> for Deprecate
             diag.subdiagnostic(diag.dcx, sub);
         }
     }
-
-    fn msg(&self) -> rustc_errors::DiagMessage {
-        match &self.since_kind {
-            DeprecatedSinceKind::InEffect => crate::fluent_generated::middle_deprecated,
-            DeprecatedSinceKind::InFuture => crate::fluent_generated::middle_deprecated_in_future,
-            DeprecatedSinceKind::InVersion(_) => {
-                crate::fluent_generated::middle_deprecated_in_version
-            }
-        }
-    }
 }
 
 fn deprecated_since_kind(is_in_effect: bool, since: DeprecatedSince) -> DeprecatedSinceKind {
@@ -598,7 +595,9 @@ impl<'tcx> TyCtxt<'tcx> {
         unmarked: impl FnOnce(Span, DefId),
     ) -> bool {
         let soft_handler = |lint, span, msg: String| {
-            self.node_span_lint(lint, id.unwrap_or(hir::CRATE_HIR_ID), span, msg, |_| {})
+            self.node_span_lint(lint, id.unwrap_or(hir::CRATE_HIR_ID), span, |lint| {
+                lint.primary_message(msg);
+            })
         };
         let eval_result =
             self.eval_stability_allow_unstable(def_id, id, span, method_span, allow_unstable);
diff --git a/compiler/rustc_middle/src/mir/interpret/queries.rs b/compiler/rustc_middle/src/mir/interpret/queries.rs
index a8518195469..fe743fa4aac 100644
--- a/compiler/rustc_middle/src/mir/interpret/queries.rs
+++ b/compiler/rustc_middle/src/mir/interpret/queries.rs
@@ -113,8 +113,7 @@ impl<'tcx> TyCtxt<'tcx> {
                                 lint::builtin::CONST_EVALUATABLE_UNCHECKED,
                                 self.local_def_id_to_hir_id(local_def_id),
                                 self.def_span(ct.def),
-                                "cannot use constants which depend on generic parameters in types",
-                                |_| {},
+                                |lint| { lint.primary_message("cannot use constants which depend on generic parameters in types"); },
                             )
                         }
                     }
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 33ce08991bb..e618323c810 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -47,9 +47,7 @@ use rustc_data_structures::sync::{self, FreezeReadGuard, Lock, Lrc, RwLock, Work
 #[cfg(parallel_compiler)]
 use rustc_data_structures::sync::{DynSend, DynSync};
 use rustc_data_structures::unord::UnordSet;
-use rustc_errors::{
-    Applicability, Diag, DiagCtxt, DiagMessage, ErrorGuaranteed, LintDiagnostic, MultiSpan,
-};
+use rustc_errors::{Applicability, Diag, DiagCtxt, ErrorGuaranteed, LintDiagnostic, MultiSpan};
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, LOCAL_CRATE};
@@ -2471,10 +2469,9 @@ impl<'tcx> TyCtxt<'tcx> {
         span: impl Into<MultiSpan>,
         decorator: impl for<'a> LintDiagnostic<'a, ()>,
     ) {
-        let msg = decorator.msg();
         let (level, src) = self.lint_level_at_node(lint, hir_id);
-        lint_level(self.sess, lint, level, src, Some(span.into()), msg, |diag| {
-            decorator.decorate_lint(diag);
+        lint_level(self.sess, lint, level, src, Some(span.into()), |lint| {
+            decorator.decorate_lint(lint);
         })
     }
 
@@ -2488,11 +2485,10 @@ impl<'tcx> TyCtxt<'tcx> {
         lint: &'static Lint,
         hir_id: HirId,
         span: impl Into<MultiSpan>,
-        msg: impl Into<DiagMessage>,
         decorate: impl for<'a, 'b> FnOnce(&'b mut Diag<'a, ()>),
     ) {
         let (level, src) = self.lint_level_at_node(lint, hir_id);
-        lint_level(self.sess, lint, level, src, Some(span.into()), msg, decorate);
+        lint_level(self.sess, lint, level, src, Some(span.into()), decorate);
     }
 
     /// Find the crate root and the appropriate span where `use` and outer attributes can be
@@ -2543,8 +2539,8 @@ impl<'tcx> TyCtxt<'tcx> {
         id: HirId,
         decorator: impl for<'a> LintDiagnostic<'a, ()>,
     ) {
-        self.node_lint(lint, id, decorator.msg(), |diag| {
-            decorator.decorate_lint(diag);
+        self.node_lint(lint, id, |lint| {
+            decorator.decorate_lint(lint);
         })
     }
 
@@ -2557,11 +2553,10 @@ impl<'tcx> TyCtxt<'tcx> {
         self,
         lint: &'static Lint,
         id: HirId,
-        msg: impl Into<DiagMessage>,
         decorate: impl for<'a, 'b> FnOnce(&'b mut Diag<'a, ()>),
     ) {
         let (level, src) = self.lint_level_at_node(lint, id);
-        lint_level(self.sess, lint, level, src, None, msg, decorate);
+        lint_level(self.sess, lint, level, src, None, decorate);
     }
 
     pub fn in_scope_traits(self, id: HirId) -> Option<&'tcx [TraitCandidate]> {
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index 0bcd02aaa3a..3c0f2578284 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -3314,7 +3314,7 @@ fn for_each_def(tcx: TyCtxt<'_>, mut collect_fn: impl for<'b> FnMut(&'b Ident, N
 ///
 /// The implementation uses similar import discovery logic to that of 'use' suggestions.
 ///
-/// See also [`DelayDm`](rustc_error_messages::DelayDm) and [`with_no_trimmed_paths!`].
+/// See also [`with_no_trimmed_paths!`].
 // this is pub to be able to intra-doc-link it
 pub fn trimmed_def_paths(tcx: TyCtxt<'_>, (): ()) -> DefIdMap<Symbol> {
     // Trimming paths is expensive and not optimized, since we expect it to only be used for error