Include reference in lint diagnostic

Author: zachs18

compiler/rustc_lint/messages.ftl

@@ -215,7 +215,7 @@ lint_expectation = this lint expectation is unfulfilled
     .rationale = {$rationale}
 
 lint_for_loops_over_fallibles =
-    for loop over {$article} `{$ty}`. This is more readably written as an `if let` statement
+    for loop over {$article} `{$ref_prefix}{$ty}`. This is more readably written as an `if let` statement
     .suggestion = consider using `if let` to clear intent
     .remove_next = to iterate over `{$recv_snip}` remove the call to `next`
     .use_while_let = to check pattern in a loop use `while let`

compiler/rustc_lint/src/for_loops_over_fallibles.rs

@@ -52,8 +52,7 @@ impl<'tcx> LateLintPass<'tcx> for ForLoopsOverFallibles {
 
         let ty = cx.typeck_results().expr_ty(arg);
 
-        // let &ty::Adt(adt, args) = ty.kind() else { return };
-        let (adt, args, _) = match ty.kind() {
+        let (adt, args, ref_mutability) = match ty.kind() {
             &ty::Adt(adt, args) => (adt, args, None),
             &ty::Ref(_, ty, mutability) => match ty.kind() {
                 &ty::Adt(adt, args) => (adt, args, Some(mutability)),
@@ -68,6 +67,11 @@ impl<'tcx> LateLintPass<'tcx> for ForLoopsOverFallibles {
             _ => return,
         };
 
+        let ref_prefix = match ref_mutability {
+            None => "",
+            Some(ref_mutability) => ref_mutability.ref_prefix_str(),
+        };
+
         let sub = if let Some(recv) = extract_iterator_next_call(cx, arg)
             && let Ok(recv_snip) = cx.sess().source_map().span_to_snippet(recv.span)
         {
@@ -93,7 +97,7 @@ impl<'tcx> LateLintPass<'tcx> for ForLoopsOverFallibles {
         cx.emit_span_lint(
             FOR_LOOPS_OVER_FALLIBLES,
             arg.span,
-            ForLoopsOverFalliblesDiag { article, ty, sub, question_mark, suggestion },
+            ForLoopsOverFalliblesDiag { article, ref_prefix, ty, sub, question_mark, suggestion },
         );
     }
 }

compiler/rustc_lint/src/lints.rs

@@ -613,6 +613,7 @@ pub enum PtrNullChecksDiag<'a> {
 #[diag(lint_for_loops_over_fallibles)]
 pub struct ForLoopsOverFalliblesDiag<'a> {
     pub article: &'static str,
+    pub ref_prefix: &'static str,
     pub ty: &'static str,
     #[subdiagnostic]
     pub sub: ForLoopsOverFalliblesLoopSub<'a>,