Auto merge of #101986 - WaffleLapkin:move_lint_note_to_the_bottom, r=estebank

Move lint level source explanation to the bottom

So, uhhhhh

r? `@estebank`

## User-facing change

"note: `#[warn(...)]` on by default" and such are moved to the bottom of the diagnostic:
```diff
-   = note: `#[warn(unsupported_calling_conventions)]` on by default
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #87678 <https://github.com/rust-lang/rust/issues/87678>
+   = note: `#[warn(unsupported_calling_conventions)]` on by default
```

Why warning is enabled is the least important thing, so it shouldn't be the first note the user reads, IMO.

## Developer-facing change

`struct_span_lint` and similar methods have a different signature.

Before: `..., impl for<'a> FnOnce(LintDiagnosticBuilder<'a, ()>)`
After: `..., impl Into<DiagnosticMessage>, impl for<'a, 'b> FnOnce(&'b mut DiagnosticBuilder<'a, ()>) -> &'b mut DiagnosticBuilder<'a, ()>`

The reason for this is that `struct_span_lint` needs to edit the diagnostic _after_ `decorate` closure is called. This also makes lint code a little bit nicer in my opinion.

Another option is to use `impl for<'a> FnOnce(LintDiagnosticBuilder<'a, ()>) -> DiagnosticBuilder<'a, ()>` altough I don't _really_ see reasons to do `let lint = lint.build(message)` everywhere.

## Subtle problem

By moving the message outside of the closure (that may not be called if the lint is disabled) `format!(...)` is executed earlier, possibly formatting `Ty` which may call a query that trims paths that crashes the compiler if there were no warnings...

I don't think it's that big of a deal, considering that we move from `format!(...)` to `fluent` (which is lazy by-default) anyway, however this required adding a workaround which is unfortunate.

## P.S.

I'm sorry, I do not how to make this PR smaller/easier to review. Changes to the lint API affect SO MUCH 😢

1 files changed, 4 insertions, 7 deletions

diff --git a/compiler/rustc_middle/src/middle/stability.rs b/compiler/rustc_middle/src/middle/stability.rs
index d182929c400..61bc089e431 100644
--- a/compiler/rustc_middle/src/middle/stability.rs
+++ b/compiler/rustc_middle/src/middle/stability.rs
@@ -253,13 +253,12 @@ fn late_report_deprecation(
         return;
     }
     let method_span = method_span.unwrap_or(span);
-    tcx.struct_span_lint_hir(lint, hir_id, method_span, |lint| {
-        let mut diag = lint.build(message);
+    tcx.struct_span_lint_hir(lint, hir_id, method_span, message, |diag| {
         if let hir::Node::Expr(_) = tcx.hir().get(hir_id) {
             let kind = tcx.def_kind(def_id).descr(def_id);
-            deprecation_suggestion(&mut diag, kind, suggestion, method_span);
+            deprecation_suggestion(diag, kind, suggestion, method_span);
         }
-        diag.emit();
+        diag
     });
 }
 
@@ -621,9 +620,7 @@ impl<'tcx> TyCtxt<'tcx> {
         unmarked: impl FnOnce(Span, DefId),
     ) -> bool {
         let soft_handler = |lint, span, msg: &_| {
-            self.struct_span_lint_hir(lint, id.unwrap_or(hir::CRATE_HIR_ID), span, |lint| {
-                lint.build(msg).emit();
-            })
+            self.struct_span_lint_hir(lint, id.unwrap_or(hir::CRATE_HIR_ID), span, msg, |lint| lint)
         };
         let eval_result =
             self.eval_stability_allow_unstable(def_id, id, span, method_span, allow_unstable);