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 #124417 (comment).

See individual commits for details. The first three commits are not strictly necessary.
However, the 2nd one (06bc4fc, *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.

Author: bors

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -576,8 +576,8 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
                     lint::builtin::INLINE_NO_SANITIZE,
                     hir_id,
                     no_sanitize_span,
-                    "`no_sanitize` will have no effect after inlining",
                     |lint| {
+                        lint.primary_message("`no_sanitize` will have no effect after inlining");
                         lint.span_note(inline_span, "inlining requested here");
                     },
                 )

compiler/rustc_error_messages/src/lib.rs

@@ -364,17 +364,6 @@ impl From<Cow<'static, str>> for DiagMessage {
     }
 }
 
-/// A workaround for must_produce_diag ICEs when formatting types in disabled lints.
-///
-/// Delays formatting until `.into(): DiagMessage` is used.
-pub struct DelayDm<F>(pub F);
-
-impl<F: FnOnce() -> String> From<DelayDm<F>> for DiagMessage {
-    fn from(DelayDm(f): DelayDm<F>) -> Self {
-        DiagMessage::from(f())
-    }
-}
-
 /// Translating *into* a subdiagnostic message from a diagnostic message is a little strange - but
 /// the subdiagnostic functions (e.g. `span_label`) take a `SubdiagMessage` and the
 /// subdiagnostic derive refers to typed identifiers that are `DiagMessage`s, so need to be