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, 13 deletions

diff --git a/compiler/rustc_hir_analysis/src/check/method/probe.rs b/compiler/rustc_hir_analysis/src/check/method/probe.rs
index 6cd7ced01a3..a761a93dea4 100644
--- a/compiler/rustc_hir_analysis/src/check/method/probe.rs
+++ b/compiler/rustc_hir_analysis/src/check/method/probe.rs
@@ -409,9 +409,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         lint::builtin::TYVAR_BEHIND_RAW_POINTER,
                         scope_expr_id,
                         span,
-                        |lint| {
-                            lint.build("type annotations needed").emit();
-                        },
+                        "type annotations needed",
+                        |lint| lint,
                     );
                 }
             } else {
@@ -1358,24 +1357,24 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         stable_pick: &Pick<'_>,
         unstable_candidates: &[(Candidate<'tcx>, Symbol)],
     ) {
+        let def_kind = stable_pick.item.kind.as_def_kind();
         self.tcx.struct_span_lint_hir(
             lint::builtin::UNSTABLE_NAME_COLLISIONS,
             self.scope_expr_id,
             self.span,
+            format!(
+                "{} {} with this name may be added to the standard library in the future",
+                def_kind.article(),
+                def_kind.descr(stable_pick.item.def_id),
+            ),
             |lint| {
-                let def_kind = stable_pick.item.kind.as_def_kind();
-                let mut diag = lint.build(&format!(
-                    "{} {} with this name may be added to the standard library in the future",
-                    def_kind.article(),
-                    def_kind.descr(stable_pick.item.def_id),
-                ));
                 match (stable_pick.item.kind, stable_pick.item.container) {
                     (ty::AssocKind::Fn, _) => {
                         // FIXME: This should be a `span_suggestion` instead of `help`
                         // However `self.span` only
                         // highlights the method name, so we can't use it. Also consider reusing
                         // the code from `report_method_error()`.
-                        diag.help(&format!(
+                        lint.help(&format!(
                             "call with fully qualified syntax `{}(...)` to keep using the current \
                              method",
                             self.tcx.def_path_str(stable_pick.item.def_id),
@@ -1383,7 +1382,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                     }
                     (ty::AssocKind::Const, ty::AssocItemContainer::TraitContainer) => {
                         let def_id = stable_pick.item.container_id(self.tcx);
-                        diag.span_suggestion(
+                        lint.span_suggestion(
                             self.span,
                             "use the fully qualified path to the associated const",
                             format!(
@@ -1399,7 +1398,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 }
                 if self.tcx.sess.is_nightly_build() {
                     for (candidate, feature) in unstable_candidates {
-                        diag.help(&format!(
+                        lint.help(&format!(
                             "add `#![feature({})]` to the crate attributes to enable `{}`",
                             feature,
                             self.tcx.def_path_str(candidate.item.def_id),
@@ -1407,7 +1406,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                     }
                 }
 
-                diag.emit();
+                lint
             },
         );
     }