Rollup merge of rust-lang#149329 - Jarcho:for_question_ctxt, r=davidtwco

JonathanBrouwer · web-flow · commit b2344865b44c · 2026-02-05T22:25:11.000+01:00
Mark match arms in try and for as being from desugarings.

Some of the arms created by these desugarings have an expression which isn't marked as coming from the desugaring. e.g. try generates `Continue(val) =&gt; val` where the expression has the span of the original parameter (done for diagnostic purposes). Since the arm created just used that span they end up without a desugaring mark unnecessarily.

This is only a minor annoyance with some work I'm doing in clippy.
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
@@ -966,14 +966,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     hir::ExprKind::Break(this.lower_loop_destination(None), Some(x_expr));
                 this.arena.alloc(this.expr(gen_future_span, expr_break))
             });
-            self.arm(ready_pat, break_x)
+            self.arm(ready_pat, break_x, span)
         };
 
         // `::std::task::Poll::Pending => {}`
         let pending_arm = {
             let pending_pat = self.pat_lang_item_variant(span, hir::LangItem::PollPending, &[]);
             let empty_block = self.expr_block_empty(span);
-            self.arm(pending_pat, empty_block)
+            self.arm(pending_pat, empty_block, span)
         };
 
         let inner_match_stmt = {
@@ -1027,7 +1027,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         });
 
         // mut __awaitee => loop { ... }
-        let awaitee_arm = self.arm(awaitee_pat, loop_expr);
+        let awaitee_arm = self.arm(awaitee_pat, loop_expr, span);
 
         // `match ::std::future::IntoFuture::into_future(<expr>) { ... }`
         let into_future_expr = match await_kind {
@@ -1817,7 +1817,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             let break_expr =
                 self.with_loop_scope(loop_hir_id, |this| this.expr_break_alloc(for_span));
             let pat = self.pat_none(for_span);
-            self.arm(pat, break_expr)
+            self.arm(pat, break_expr, for_span)
         };
 
         // Some(<pat>) => <body>,
@@ -1826,7 +1826,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             let body_block =
                 self.with_loop_scope(loop_hir_id, |this| this.lower_block(body, false));
             let body_expr = self.arena.alloc(self.expr_block(body_block));
-            self.arm(some_pat, body_expr)
+            self.arm(some_pat, body_expr, for_span)
         };
 
         // `mut iter`
@@ -1885,7 +1885,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let loop_expr = self.arena.alloc(hir::Expr { hir_id: loop_hir_id, kind, span: for_span });
 
         // `mut iter => { ... }`
-        let iter_arm = self.arm(iter_pat, loop_expr);
+        let iter_arm = self.arm(iter_pat, loop_expr, for_span);
 
         let match_expr = match loop_kind {
             ForLoopKind::For => {
@@ -1930,7 +1930,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     hir::LangItem::IntoAsyncIterIntoIter,
                     arena_vec![self; head],
                 );
-                let iter_arm = self.arm(async_iter_pat, inner_match_expr);
+                let iter_arm = self.arm(async_iter_pat, inner_match_expr, for_span);
                 self.arena.alloc(self.expr_match(
                     for_span,
                     iter,
@@ -1997,7 +1997,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             let val_expr = self.expr_ident(span, val_ident, val_pat_nid);
             self.lower_attrs(val_expr.hir_id, &attrs, span, Target::Expression);
             let continue_pat = self.pat_cf_continue(unstable_span, val_pat);
-            self.arm(continue_pat, val_expr)
+            self.arm(continue_pat, val_expr, try_span)
         };
 
         // `ControlFlow::Break(residual) =>
@@ -2040,7 +2040,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             self.lower_attrs(ret_expr.hir_id, &attrs, span, Target::Expression);
 
             let break_pat = self.pat_cf_break(try_span, residual_local);
-            self.arm(break_pat, ret_expr)
+            self.arm(break_pat, ret_expr, try_span)
         };
 
         hir::ExprKind::Match(
@@ -2368,12 +2368,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
         &mut self,
         pat: &'hir hir::Pat<'hir>,
         expr: &'hir hir::Expr<'hir>,
+        span: Span,
     ) -> hir::Arm<'hir> {
         hir::Arm {
             hir_id: self.next_id(),
             pat,
             guard: None,
-            span: self.lower_span(expr.span),
+            span: self.lower_span(span),
             body: expr,
         }
     }
