Feature gate

9 files changed, 76 insertions, 9 deletions

diff --git a/compiler/rustc_ast_passes/src/feature_gate.rs b/compiler/rustc_ast_passes/src/feature_gate.rs
index bb83f4c0f0e..5912dd3f931 100644
--- a/compiler/rustc_ast_passes/src/feature_gate.rs
+++ b/compiler/rustc_ast_passes/src/feature_gate.rs
@@ -565,6 +565,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
     gate_all!(unnamed_fields, "unnamed fields are not yet fully implemented");
     gate_all!(fn_delegation, "functions delegation is not yet fully implemented");
     gate_all!(postfix_match, "postfix match is experimental");
+    gate_all!(mut_ref, "mutable by-reference bindings are experimental");
 
     if !visitor.features.never_patterns {
         if let Some(spans) = spans.get(&sym::never_patterns) {
diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
index 8d72f4924d6..4c975c7b9e0 100644
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@@ -529,6 +529,8 @@ declare_features! (
     (unstable, more_qualified_paths, "1.54.0", Some(86935)),
     /// Allows the `#[must_not_suspend]` attribute.
     (unstable, must_not_suspend, "1.57.0", Some(83310)),
+    /// Allows `mut ref` and `mut ref mut` identifier patterns.
+    (incomplete, mut_ref, "CURRENT_RUSTC_VERSION", Some(123076)),
     /// Allows using `#[naked]` on functions.
     (unstable, naked_functions, "1.9.0", Some(90957)),
     /// Allows specifying the as-needed link modifier
diff --git a/compiler/rustc_parse/src/parser/pat.rs b/compiler/rustc_parse/src/parser/pat.rs
index ead00c3f0d4..59e0cd92c4c 100644
--- a/compiler/rustc_parse/src/parser/pat.rs
+++ b/compiler/rustc_parse/src/parser/pat.rs
@@ -779,6 +779,10 @@ impl<'a> Parser<'a> {
             self.ban_mut_general_pat(mut_span, &pat, changed_any_binding);
         }
 
+        if matches!(pat.kind, PatKind::Ident(BindingAnnotation(ByRef::Yes(_), Mutability::Mut), ..))
+        {
+            self.psess.gated_spans.gate(sym::mut_ref, pat.span);
+        }
         Ok(pat.into_inner().kind)
     }
 
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 891ddb7af5b..15fba5645e2 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -1185,6 +1185,7 @@ symbols! {
         multiple_supertrait_upcastable,
         must_not_suspend,
         must_use,
+        mut_ref,
         naked,
         naked_functions,
         name,
diff --git a/tests/ui/feature-gates/feature-gate-mut-ref.rs b/tests/ui/feature-gates/feature-gate-mut-ref.rs
new file mode 100644
index 00000000000..806b25de66f
--- /dev/null
+++ b/tests/ui/feature-gates/feature-gate-mut-ref.rs
@@ -0,0 +1,13 @@
+fn main() {
+    let mut ref x = 10; //~  ERROR [E0658]
+    x = &11;
+    let ref mut y = 12;
+    *y = 13;
+    let mut ref mut z = 14; //~  ERROR [E0658]
+    z = &mut 15;
+
+    #[cfg(FALSE)]
+    let mut ref x = 10; //~  ERROR [E0658]
+    #[cfg(FALSE)]
+    let mut ref mut y = 10; //~  ERROR [E0658]
+}
diff --git a/tests/ui/feature-gates/feature-gate-mut-ref.stderr b/tests/ui/feature-gates/feature-gate-mut-ref.stderr
new file mode 100644
index 00000000000..d3eb674e92d
--- /dev/null
+++ b/tests/ui/feature-gates/feature-gate-mut-ref.stderr
@@ -0,0 +1,43 @@
+error[E0658]: mutable by-reference bindings are experimental
+  --> $DIR/feature-gate-mut-ref.rs:2:17
+   |
+LL |     let mut ref x = 10;
+   |                 ^
+   |
+   = 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[E0658]: mutable by-reference bindings are experimental
+  --> $DIR/feature-gate-mut-ref.rs:6:21
+   |
+LL |     let mut ref mut z = 14;
+   |                     ^
+   |
+   = 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[E0658]: mutable by-reference bindings are experimental
+  --> $DIR/feature-gate-mut-ref.rs:10:17
+   |
+LL |     let mut ref x = 10;
+   |                 ^
+   |
+   = 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[E0658]: mutable by-reference bindings are experimental
+  --> $DIR/feature-gate-mut-ref.rs:12:21
+   |
+LL |     let mut ref mut y = 10;
+   |                     ^
+   |
+   = 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 4 previous errors
+
+For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/mut/mut-ref.rs b/tests/ui/mut/mut-ref.rs
index 813c7f02df1..54630d95007 100644
--- a/tests/ui/mut/mut-ref.rs
+++ b/tests/ui/mut/mut-ref.rs
@@ -1,5 +1,6 @@
 //@ check-pass
-
+#![allow(incomplete_features)]
+#![feature(mut_ref)]
 fn main() {
     let mut ref x = 10;
     x = &11;
diff --git a/tests/ui/match/mut-ref-mut-2021.rs b/tests/ui/pattern/mut-ref-mut-2021.rs
index 48516350d4d..a3be40faeff 100644
--- a/tests/ui/match/mut-ref-mut-2021.rs
+++ b/tests/ui/pattern/mut-ref-mut-2021.rs
@@ -1,4 +1,6 @@
 //@ edition: 2021
+#![allow(incomplete_features)]
+#![feature(mut_ref)]
 
 struct Foo(u8);
 
diff --git a/tests/ui/match/mut-ref-mut-2021.stderr b/tests/ui/pattern/mut-ref-mut-2021.stderr
index 9210ce23784..eb31ffa0e30 100644
--- a/tests/ui/match/mut-ref-mut-2021.stderr
+++ b/tests/ui/pattern/mut-ref-mut-2021.stderr
@@ -1,5 +1,5 @@
 error[E0384]: cannot assign twice to immutable variable `a`
-  --> $DIR/mut-ref-mut-2021.rs:7:5
+  --> $DIR/mut-ref-mut-2021.rs:9:5
    |
 LL |     let Foo(a) = Foo(0);
    |             -
@@ -10,7 +10,7 @@ LL |     a = 42;
    |     ^^^^^^ cannot assign twice to immutable variable
 
 error[E0384]: cannot assign twice to immutable variable `a`
-  --> $DIR/mut-ref-mut-2021.rs:13:5
+  --> $DIR/mut-ref-mut-2021.rs:15:5
    |
 LL |     let Foo(ref a) = Foo(0);
    |             ----- first assignment to `a`
@@ -18,7 +18,7 @@ LL |     a = &42;
    |     ^^^^^^^ cannot assign twice to immutable variable
 
 error[E0384]: cannot assign twice to immutable variable `a`
-  --> $DIR/mut-ref-mut-2021.rs:19:5
+  --> $DIR/mut-ref-mut-2021.rs:21:5
    |
 LL |     let Foo(ref mut a) = Foo(0);
    |             --------- first assignment to `a`
@@ -26,7 +26,7 @@ LL |     a = &mut 42;
    |     ^^^^^^^^^^^ cannot assign twice to immutable variable
 
 error[E0384]: cannot assign twice to immutable variable `a`
-  --> $DIR/mut-ref-mut-2021.rs:25:5
+  --> $DIR/mut-ref-mut-2021.rs:27:5
    |
 LL |     let Foo(a) = &Foo(0);
    |             - first assignment to `a`
@@ -34,7 +34,7 @@ LL |     a = &42;
    |     ^^^^^^^ cannot assign twice to immutable variable
 
 error[E0384]: cannot assign twice to immutable variable `a`
-  --> $DIR/mut-ref-mut-2021.rs:31:5
+  --> $DIR/mut-ref-mut-2021.rs:33:5
    |
 LL |     let Foo(ref a) = &Foo(0);
    |             ----- first assignment to `a`
@@ -42,7 +42,7 @@ LL |     a = &42;
    |     ^^^^^^^ cannot assign twice to immutable variable
 
 error[E0384]: cannot assign twice to immutable variable `a`
-  --> $DIR/mut-ref-mut-2021.rs:37:5
+  --> $DIR/mut-ref-mut-2021.rs:39:5
    |
 LL |     let Foo(a) = &mut Foo(0);
    |             - first assignment to `a`
@@ -50,7 +50,7 @@ LL |     a = &mut 42;
    |     ^^^^^^^^^^^ cannot assign twice to immutable variable
 
 error[E0384]: cannot assign twice to immutable variable `a`
-  --> $DIR/mut-ref-mut-2021.rs:43:5
+  --> $DIR/mut-ref-mut-2021.rs:45:5
    |
 LL |     let Foo(ref a) = &mut Foo(0);
    |             ----- first assignment to `a`
@@ -58,7 +58,7 @@ LL |     a = &42;
    |     ^^^^^^^ cannot assign twice to immutable variable
 
 error[E0384]: cannot assign twice to immutable variable `a`
-  --> $DIR/mut-ref-mut-2021.rs:49:5
+  --> $DIR/mut-ref-mut-2021.rs:51:5
    |
 LL |     let Foo(ref mut a) = &mut Foo(0);
    |             --------- first assignment to `a`