Auto merge of #93259 - eddyb:diagbld-scalar-pair, r=jackh726

rustc_errors: only box the `diagnostic` field in `DiagnosticBuilder`.

I happened to need to do the first change (replacing `allow_suggestions` with equivalent functionality on `Diagnostic` itself) as part of a larger change, and noticed that there's only two fields left in `DiagnosticBuilderInner`.

So with this PR, instead of a single pointer, `DiagnosticBuilder` is two pointers, which should work just as well for passing *it* by value (and may even work better wrt some operations, though probably not by much).

But anything that was already taking advantage of `DiagnosticBuilder` being a single pointer, and wrapping it further (e.g. `Result<T, DiagnosticBuilder>` w/ non-ZST `T`), ~~will probably see a slowdown~~, so I want to do a perf run before even trying to propose this.

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/rustc_middle/src/lint.rs b/compiler/rustc_middle/src/lint.rs
index eef10356ed2..c6226c69f30 100644
--- a/compiler/rustc_middle/src/lint.rs
+++ b/compiler/rustc_middle/src/lint.rs
@@ -262,7 +262,7 @@ pub fn struct_lint_level<'s, 'd>(
         if err.span.primary_spans().iter().any(|s| in_external_macro(sess, *s)) {
             // Any suggestions made here are likely to be incorrect, so anything we
             // emit shouldn't be automatically fixed by rustfix.
-            err.allow_suggestions(false);
+            err.disable_suggestions();
 
             // If this is a future incompatible that is not an edition fixing lint
             // it'll become a hard error, so we have to emit *something*. Also,