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, 14 insertions, 15 deletions

diff --git a/compiler/rustc_passes/src/stability.rs b/compiler/rustc_passes/src/stability.rs
index e50beb27d2a..34fa80228df 100644
--- a/compiler/rustc_passes/src/stability.rs
+++ b/compiler/rustc_passes/src/stability.rs
@@ -752,10 +752,8 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
                                 INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
                                 item.hir_id(),
                                 span,
-                                |lint| {lint
-                                    .build("an `#[unstable]` annotation here has no effect")
-                                    .note("see issue #55436 <https://github.com/rust-lang/rust/issues/55436> for more information")
-                                    .emit();}
+                                "an `#[unstable]` annotation here has no effect",
+                                |lint| lint.note("see issue #55436 <https://github.com/rust-lang/rust/issues/55436> for more information")
                             );
                         }
                     }
@@ -1081,11 +1079,16 @@ fn unnecessary_partially_stable_feature_lint(
     implies: Symbol,
     since: Symbol,
 ) {
-    tcx.struct_span_lint_hir(lint::builtin::STABLE_FEATURES, hir::CRATE_HIR_ID, span, |lint| {
-        lint.build(&format!(
+    tcx.struct_span_lint_hir(
+        lint::builtin::STABLE_FEATURES,
+        hir::CRATE_HIR_ID,
+        span,
+        format!(
             "the feature `{feature}` has been partially stabilized since {since} and is succeeded \
              by the feature `{implies}`"
-        ))
+        ),
+        |lint| {
+            lint
         .span_suggestion(
             span,
             &format!(
@@ -1100,8 +1103,8 @@ fn unnecessary_partially_stable_feature_lint(
             "",
             Applicability::MaybeIncorrect,
         )
-        .emit();
-    });
+        },
+    );
 }
 
 fn unnecessary_stable_feature_lint(
@@ -1113,12 +1116,8 @@ fn unnecessary_stable_feature_lint(
     if since.as_str() == VERSION_PLACEHOLDER {
         since = rust_version_symbol();
     }
-    tcx.struct_span_lint_hir(lint::builtin::STABLE_FEATURES, hir::CRATE_HIR_ID, span, |lint| {
-        lint.build(&format!(
-            "the feature `{feature}` has been stable since {since} and no longer requires an \
-             attribute to enable",
-        ))
-        .emit();
+    tcx.struct_span_lint_hir(lint::builtin::STABLE_FEATURES, hir::CRATE_HIR_ID, span, format!("the feature `{feature}` has been stable since {since} and no longer requires an attribute to enable"), |lint| {
+        lint
     });
 }