Gate implicit mutable by-reference bindings behind mut ref

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_fail.rs

@@ -49,4 +49,14 @@ pub fn main() {
 
     let &mut &mut &mut &mut _ = &mut &&&&mut &&&mut &mut 0;
     //~^ ERROR: mismatched types
+
+    struct Foo(u8);
+
+    let Foo(mut a) = &Foo(0);
+    //~^ ERROR: binding cannot be both mutable and by-reference
+    a = &42;
+
+    let Foo(mut a) = &mut Foo(0);
+    //~^ ERROR: binding cannot be both mutable and by-reference
+    a = &mut 42;
 }

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_fail.stderr

@@ -152,6 +152,27 @@ LL |     let &mut &mut &mut &mut _ = &mut &&&&mut &&&mut &mut 0;
    = note:      expected reference `&&&&mut &&&mut &mut {integer}`
            found mutable reference `&mut _`
 
-error: aborting due to 14 previous errors
+error[E0658]: binding cannot be both mutable and by-reference
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:55:13
+   |
+LL |     let Foo(mut a) = &Foo(0);
+   |             ^^^^
+   |
+   = note: see issue #123076 <https://github.com/rust-lang/rust/issues/123076> for more information
+   = help: add `#![feature(mut_ref)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-For more information about this error, try `rustc --explain E0308`.
+error[E0658]: binding cannot be both mutable and by-reference
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:59:13
+   |
+LL |     let Foo(mut a) = &mut Foo(0);
+   |             ^^^^
+   |
+   = note: see issue #123076 <https://github.com/rust-lang/rust/issues/123076> for more information
+   = help: add `#![feature(mut_ref)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: aborting due to 16 previous errors
+
+Some errors have detailed explanations: E0308, E0658.
+For more information about an error, try `rustc --explain E0308`.

tests/ui/pattern/feature-gate-mut_preserve_binding_mode_2024.rs

@@ -1,14 +0,0 @@
-//@ edition: 2024
-//@ compile-flags: -Zunstable-options
-
-struct Foo(u8);
-
-fn main() {
-    let Foo(mut a) = &Foo(0);
-    a = &42;
-    //~^ ERROR: mismatched types
-
-    let Foo(mut a) = &mut Foo(0);
-    a = &mut 42;
-    //~^ ERROR: mismatched types
-}

tests/ui/pattern/feature-gate-mut_preserve_binding_mode_2024.stderr

@@ -1,31 +0,0 @@
-error[E0308]: mismatched types
-  --> $DIR/feature-gate-mut_preserve_binding_mode_2024.rs:8:9
-   |
-LL |     let Foo(mut a) = &Foo(0);
-   |             ----- expected due to the type of this binding
-LL |     a = &42;
-   |         ^^^ expected `u8`, found `&{integer}`
-   |
-help: consider removing the borrow
-   |
-LL -     a = &42;
-LL +     a = 42;
-   |
-
-error[E0308]: mismatched types
-  --> $DIR/feature-gate-mut_preserve_binding_mode_2024.rs:12:9
-   |
-LL |     let Foo(mut a) = &mut Foo(0);
-   |             ----- expected due to the type of this binding
-LL |     a = &mut 42;
-   |         ^^^^^^^ expected `u8`, found `&mut {integer}`
-   |
-help: consider removing the borrow
-   |
-LL -     a = &mut 42;
-LL +     a = 42;
-   |
-
-error: aborting due to 2 previous errors
-
-For more information about this error, try `rustc --explain E0308`.

tests/ui/pattern/match_ergonomics_2024.fixed

@@ -2,7 +2,7 @@
 //@ run-rustfix
 //@ rustfix-only-machine-applicable
 //@ aux-build:match_ergonomics_2024_macros.rs
-#![feature(mut_preserve_binding_mode_2024, ref_pat_eat_one_layer_2024)]
+#![feature(mut_ref, ref_pat_eat_one_layer_2024)]
 #![allow(incomplete_features, unused)]
 #![deny(rust_2024_incompatible_pat)]
 

tests/ui/pattern/match_ergonomics_2024.rs

@@ -2,7 +2,7 @@
 //@ run-rustfix
 //@ rustfix-only-machine-applicable
 //@ aux-build:match_ergonomics_2024_macros.rs
-#![feature(mut_preserve_binding_mode_2024, ref_pat_eat_one_layer_2024)]
+#![feature(mut_ref, ref_pat_eat_one_layer_2024)]
 #![allow(incomplete_features, unused)]
 #![deny(rust_2024_incompatible_pat)]
 

tests/ui/pattern/mut_preserve_binding_mode_2021.rs

@@ -1,6 +1,6 @@
 //@ edition: 2021
 //@ compile-flags: -Zunstable-options
-#![feature(mut_preserve_binding_mode_2024)]
+#![feature(ref_pat_eat_one_layer_2024)]
 #![allow(incomplete_features)]
 
 struct Foo(u8);

tests/ui/pattern/mut_preserve_binding_mode_2024.rs

@@ -1,7 +1,7 @@
 //@ run-pass
 //@ edition: 2024
 //@ compile-flags: -Zunstable-options
-#![feature(mut_preserve_binding_mode_2024)]
+#![feature(mut_ref, ref_pat_eat_one_layer_2024)]
 #![allow(incomplete_features, unused)]
 
 struct Foo(u8);