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.

1 files changed, 9 insertions, 16 deletions

diff --git a/compiler/rustc_lint_defs/src/lib.rs b/compiler/rustc_lint_defs/src/lib.rs
index 1941b0b1264..c8a9fb02bf2 100644
--- a/compiler/rustc_lint_defs/src/lib.rs
+++ b/compiler/rustc_lint_defs/src/lib.rs
@@ -764,19 +764,7 @@ pub struct LintBuffer {
 
 impl LintBuffer {
     pub fn add_early_lint(&mut self, early_lint: BufferedEarlyLint) {
-        let arr = self.map.entry(early_lint.node_id).or_default();
-        arr.push(early_lint);
-    }
-
-    pub fn add_lint(
-        &mut self,
-        lint: &'static Lint,
-        node_id: NodeId,
-        span: MultiSpan,
-        diagnostic: BuiltinLintDiag,
-    ) {
-        let lint_id = LintId::of(lint);
-        self.add_early_lint(BufferedEarlyLint { lint_id, node_id, span, diagnostic });
+        self.map.entry(early_lint.node_id).or_default().push(early_lint);
     }
 
     pub fn take(&mut self, id: NodeId) -> Vec<BufferedEarlyLint> {
@@ -787,11 +775,16 @@ impl LintBuffer {
     pub fn buffer_lint(
         &mut self,
         lint: &'static Lint,
-        id: NodeId,
-        sp: impl Into<MultiSpan>,
+        node_id: NodeId,
+        span: impl Into<MultiSpan>,
         diagnostic: BuiltinLintDiag,
     ) {
-        self.add_lint(lint, id, sp.into(), diagnostic)
+        self.add_early_lint(BufferedEarlyLint {
+            lint_id: LintId::of(lint),
+            node_id,
+            span: span.into(),
+            diagnostic,
+        });
     }
 }