Avoid lowering a MacArgs::Eq twice.

Fixes #96847.

Author: nnethercote

compiler/rustc_ast_lowering/src/expr.rs

@@ -1534,15 +1534,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
             hir::MatchSource::ForLoopDesugar,
         ));
 
-        let attrs: Vec<_> = e.attrs.iter().map(|a| self.lower_attr(a)).collect();
-
         // This is effectively `{ let _result = ...; _result }`.
         // The construct was introduced in #21984 and is necessary to make sure that
         // temporaries in the `head` expression are dropped and do not leak to the
         // 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(for_span, match_expr, attrs.into())
+        self.expr_drop_temps_mut(for_span, match_expr, e.attrs.clone())
     }
 
     /// Desugar `ExprKind::Try` from: `<expr>?` into:

src/test/ui/lowering/issue-96847.rs

@@ -0,0 +1,14 @@
+// run-pass
+
+// Test that this doesn't abort during AST lowering. In #96847 it did abort
+// because the attribute was being lowered twice.
+
+#![feature(stmt_expr_attributes)]
+#![feature(lang_items)]
+
+fn main() {
+    for _ in [1,2,3] {
+        #![lang="foo"]
+        println!("foo");
+    }
+}