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, 12 insertions, 11 deletions

diff --git a/compiler/rustc_hir_analysis/src/coherence/orphan.rs b/compiler/rustc_hir_analysis/src/coherence/orphan.rs
index 7d15e5a7f3c..1307f74f210 100644
--- a/compiler/rustc_hir_analysis/src/coherence/orphan.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/orphan.rs
@@ -2,7 +2,7 @@
 //! crate or pertains to a type defined in this crate.
 
 use rustc_data_structures::fx::FxHashSet;
-use rustc_errors::struct_span_err;
+use rustc_errors::{struct_span_err, DelayDm};
 use rustc_errors::{Diagnostic, ErrorGuaranteed};
 use rustc_hir as hir;
 use rustc_middle::ty::subst::GenericArgKind;
@@ -412,30 +412,31 @@ fn lint_auto_trait_impl<'tcx>(
         lint::builtin::SUSPICIOUS_AUTO_TRAIT_IMPLS,
         tcx.hir().local_def_id_to_hir_id(impl_def_id),
         tcx.def_span(impl_def_id),
-        |err| {
-            let item_span = tcx.def_span(self_type_did);
-            let self_descr = tcx.def_kind(self_type_did).descr(self_type_did);
-            let mut err = err.build(&format!(
+        DelayDm(|| {
+            format!(
                 "cross-crate traits with a default impl, like `{}`, \
                          should not be specialized",
                 tcx.def_path_str(trait_ref.def_id),
-            ));
+            )
+        }),
+        |lint| {
+            let item_span = tcx.def_span(self_type_did);
+            let self_descr = tcx.def_kind(self_type_did).descr(self_type_did);
             match arg {
                 ty::util::NotUniqueParam::DuplicateParam(arg) => {
-                    err.note(&format!("`{}` is mentioned multiple times", arg));
+                    lint.note(&format!("`{}` is mentioned multiple times", arg));
                 }
                 ty::util::NotUniqueParam::NotParam(arg) => {
-                    err.note(&format!("`{}` is not a generic parameter", arg));
+                    lint.note(&format!("`{}` is not a generic parameter", arg));
                 }
             }
-            err.span_note(
+            lint.span_note(
                 item_span,
                 &format!(
                     "try using the same sequence of generic parameters as the {} definition",
                     self_descr,
                 ),
-            );
-            err.emit();
+            )
         },
     );
 }