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, 11 insertions, 7 deletions

diff --git a/compiler/rustc_hir_analysis/src/check/check.rs b/compiler/rustc_hir_analysis/src/check/check.rs
index 4bbe9abaf98..824144aeac0 100644
--- a/compiler/rustc_hir_analysis/src/check/check.rs
+++ b/compiler/rustc_hir_analysis/src/check/check.rs
@@ -48,9 +48,13 @@ pub(super) fn check_abi(tcx: TyCtxt<'_>, hir_id: hir::HirId, span: Span, abi: Ab
             .emit();
         }
         None => {
-            tcx.struct_span_lint_hir(UNSUPPORTED_CALLING_CONVENTIONS, hir_id, span, |lint| {
-                lint.build("use of calling convention not supported on this target").emit();
-            });
+            tcx.struct_span_lint_hir(
+                UNSUPPORTED_CALLING_CONVENTIONS,
+                hir_id,
+                span,
+                "use of calling convention not supported on this target",
+                |lint| lint,
+            );
         }
     }
 
@@ -510,10 +514,10 @@ fn check_static_inhabited<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) {
             UNINHABITED_STATIC,
             tcx.hir().local_def_id_to_hir_id(def_id),
             span,
+            "static of uninhabited type",
             |lint| {
-                lint.build("static of uninhabited type")
+                lint
                 .note("uninhabited statics cannot be initialized, and any access would be an immediate error")
-                .emit();
             },
         );
     }
@@ -1437,6 +1441,7 @@ pub(super) fn check_transparent<'tcx>(tcx: TyCtxt<'tcx>, sp: Span, adt: ty::AdtD
                 REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS,
                 tcx.hir().local_def_id_to_hir_id(adt.did().expect_local()),
                 span,
+                "zero-sized fields in `repr(transparent)` cannot contain external non-exhaustive types",
                 |lint| {
                     let note = if non_exhaustive {
                         "is marked with `#[non_exhaustive]`"
@@ -1444,10 +1449,9 @@ pub(super) fn check_transparent<'tcx>(tcx: TyCtxt<'tcx>, sp: Span, adt: ty::AdtD
                         "contains private fields"
                     };
                     let field_ty = tcx.def_path_str_with_substs(def_id, substs);
-                    lint.build("zero-sized fields in repr(transparent) cannot contain external non-exhaustive types")
+                    lint
                         .note(format!("this {descr} contains `{field_ty}`, which {note}, \
                             and makes it not a breaking change to become non-zero-sized in the future."))
-                        .emit();
                 },
             )
         }