Match ergonomics 2024: & matches &mut on old editions

Author: Jules-Bertholet

compiler/rustc_hir_typeck/src/pat.rs

@@ -2217,7 +2217,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 debug!("check_pat_ref: expected={:?}", expected);
                 match *expected.kind() {
                     ty::Ref(_, r_ty, r_mutbl)
-                        if (new_match_ergonomics && r_mutbl >= pat_mutbl)
+                        if (no_ref_mut_behind_and && r_mutbl >= pat_mutbl)
                             || r_mutbl == pat_mutbl =>
                     {
                         if no_ref_mut_behind_and && r_mutbl == Mutability::Not {

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2021.rs

@@ -0,0 +1,15 @@
+//@ run-pass
+//@ edition: 2021
+//@ revisions: classic structural both
+#![allow(incomplete_features)]
+#![cfg_attr(any(classic, both), feature(ref_pat_eat_one_layer_2024))]
+#![cfg_attr(any(structural, both), feature(ref_pat_eat_one_layer_2024_structural))]
+
+pub fn main() {
+    if let &Some(Some(x)) = &Some(&mut Some(0)) {
+        let _: &u32 = x;
+    }
+    if let Some(&x) = Some(&mut 0) {
+        let _: u32 = x;
+    }
+}