Auto merge of #88214 - notriddle:notriddle/for-loop-span-drop-temps-mut, r=nagisa

rustc: use more correct span data in for loop desugaring

Fixes #82462

Before:

      help: consider adding semicolon after the expression so its temporaries are dropped sooner, before the local variables declared by the block are dropped
         |
      LL |     for x in DroppingSlice(&*v).iter(); {
         |                                       +

After:

      help: consider adding semicolon after the expression so its temporaries are dropped sooner, before the local variables declared by the block are dropped
         |
      LL |     };
         |      +

This seems like a reasonable fix: since the desugared "expr_drop_temps_mut" contains the entire desugared loop construct, its span should contain the entire loop construct as well.

1 files changed, 7 insertions, 2 deletions

diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index 16cd7a0bcdd..26b1052e0de 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -1450,8 +1450,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
             )
         };
 
+        // #82462: to correctly diagnose borrow errors, the block that contains
+        // the iter expr needs to have a span that covers the loop body.
+        let desugared_full_span =
+            self.mark_span_with_reason(DesugaringKind::ForLoop(ForLoopLoc::Head), e.span, None);
+
         let match_expr = self.arena.alloc(self.expr_match(
-            desugared_span,
+            desugared_full_span,
             into_iter_expr,
             arena_vec![self; iter_arm],
             hir::MatchSource::ForLoopDesugar,
@@ -1465,7 +1470,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         // surrounding scope of the `match` since the `match` is not a terminating scope.
         //
         // Also, add the attributes to the outer returned expr node.
-        self.expr_drop_temps_mut(desugared_span, match_expr, attrs.into())
+        self.expr_drop_temps_mut(desugared_full_span, match_expr, attrs.into())
     }
 
     /// Desugar `ExprKind::Try` from: `<expr>?` into: