Rollup merge of #127369 - Jules-Bertholet:match-ergonomics-2021, r=Nadrieril

Match ergonomics 2024: align with RFC again

- `&` matches `&mut` on old editions
- Add some more tests

r? ``@Nadrieril``

cc https://github.com/rust-lang/rust/issues/123076

``@rustbot`` label A-edition-2024 A-patterns

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

@@ -1,37 +1,15 @@
+//@ run-pass
 //@ edition: 2021
+//@ revisions: classic structural both
 #![allow(incomplete_features)]
-#![feature(ref_pat_eat_one_layer_2024)]
+#![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(&Some(0)) {
-        //~^ ERROR: mismatched types
-        let _: u32 = x;
-    }
-    if let Some(Some(&x)) = &Some(Some(&0)) {
+    if let &Some(Some(x)) = &Some(&mut Some(0)) {
         let _: &u32 = x;
-        //~^ ERROR: mismatched types
     }
-    if let Some(Some(&&x)) = &Some(Some(&0)) {
-        //~^ ERROR: mismatched types
-        let _: u32 = x;
-    }
-    if let Some(&Some(x)) = &Some(Some(0)) {
-        //~^ ERROR: mismatched types
-        let _: u32 = x;
-    }
-    if let Some(Some(&mut x)) = &mut Some(&mut Some(0)) {
-        //~^ ERROR: mismatched types
-        let _: u32 = x;
-    }
-    if let Some(Some(&x)) = &Some(&Some(0)) {
-        //~^ ERROR: mismatched types
-        let _: u32 = x;
-    }
-    if let Some(&mut Some(&x)) = &Some(&mut Some(0)) {
-        //~^ ERROR: mismatched types
-        let _: u32 = x;
-    }
-    if let Some(&Some(&mut x)) = &mut Some(&Some(0)) {
-        //~^ ERROR: mismatched types
+    if let Some(&x) = Some(&mut 0) {
         let _: u32 = x;
     }
 }

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2021_fail.rs

@@ -0,0 +1,37 @@
+//@ edition: 2021
+#![allow(incomplete_features)]
+#![feature(ref_pat_eat_one_layer_2024)]
+pub fn main() {
+    if let Some(Some(&x)) = &Some(&Some(0)) {
+        //~^ ERROR: mismatched types
+        let _: u32 = x;
+    }
+    if let Some(Some(&x)) = &Some(Some(&0)) {
+        let _: &u32 = x;
+        //~^ ERROR: mismatched types
+    }
+    if let Some(Some(&&x)) = &Some(Some(&0)) {
+        //~^ ERROR: mismatched types
+        let _: u32 = x;
+    }
+    if let Some(&Some(x)) = &Some(Some(0)) {
+        //~^ ERROR: mismatched types
+        let _: u32 = x;
+    }
+    if let Some(Some(&mut x)) = &mut Some(&mut Some(0)) {
+        //~^ ERROR: mismatched types
+        let _: u32 = x;
+    }
+    if let Some(Some(&x)) = &Some(&Some(0)) {
+        //~^ ERROR: mismatched types
+        let _: u32 = x;
+    }
+    if let Some(&mut Some(&x)) = &Some(&mut Some(0)) {
+        //~^ ERROR: mismatched types
+        let _: u32 = x;
+    }
+    if let Some(&Some(&mut x)) = &mut Some(&Some(0)) {
+        //~^ ERROR: mismatched types
+        let _: u32 = x;
+    }
+}

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2021_fail.stderr

@@ -1,5 +1,5 @@
 error[E0308]: mismatched types
-  --> $DIR/ref_pat_eat_one_layer_2021.rs:5:22
+  --> $DIR/ref_pat_eat_one_layer_2021_fail.rs:5:22
    |
 LL |     if let Some(Some(&x)) = &Some(&Some(0)) {
    |                      ^^     --------------- this expression has type `&Option<&Option<{integer}>>`
@@ -14,7 +14,7 @@ LL |     if let Some(Some(x)) = &Some(&Some(0)) {
    |                      ~
 
 error[E0308]: mismatched types
-  --> $DIR/ref_pat_eat_one_layer_2021.rs:10:23
+  --> $DIR/ref_pat_eat_one_layer_2021_fail.rs:10:23
    |
 LL |         let _: &u32 = x;
    |                ----   ^ expected `&u32`, found integer
@@ -27,7 +27,7 @@ LL |         let _: &u32 = &x;
    |                       +
 
 error[E0308]: mismatched types
-  --> $DIR/ref_pat_eat_one_layer_2021.rs:13:23
+  --> $DIR/ref_pat_eat_one_layer_2021_fail.rs:13:23
    |
 LL |     if let Some(Some(&&x)) = &Some(Some(&0)) {
    |                       ^^     --------------- this expression has type `&Option<Option<&{integer}>>`
@@ -43,7 +43,7 @@ LL +     if let Some(Some(&x)) = &Some(Some(&0)) {
    |
 
 error[E0308]: mismatched types
-  --> $DIR/ref_pat_eat_one_layer_2021.rs:17:17
+  --> $DIR/ref_pat_eat_one_layer_2021_fail.rs:17:17
    |
 LL |     if let Some(&Some(x)) = &Some(Some(0)) {
    |                 ^^^^^^^^    -------------- this expression has type `&Option<Option<{integer}>>`
@@ -54,7 +54,7 @@ LL |     if let Some(&Some(x)) = &Some(Some(0)) {
            found reference `&_`
 
 error[E0308]: mismatched types
-  --> $DIR/ref_pat_eat_one_layer_2021.rs:21:22
+  --> $DIR/ref_pat_eat_one_layer_2021_fail.rs:21:22
    |
 LL |     if let Some(Some(&mut x)) = &mut Some(&mut Some(0)) {
    |                      ^^^^^^     ----------------------- this expression has type `&mut Option<&mut Option<{integer}>>`
@@ -64,7 +64,7 @@ LL |     if let Some(Some(&mut x)) = &mut Some(&mut Some(0)) {
    = note:           expected type `{integer}`
            found mutable reference `&mut _`
 note: to declare a mutable binding use: `mut x`
-  --> $DIR/ref_pat_eat_one_layer_2021.rs:21:22
+  --> $DIR/ref_pat_eat_one_layer_2021_fail.rs:21:22
    |
 LL |     if let Some(Some(&mut x)) = &mut Some(&mut Some(0)) {
    |                      ^^^^^^
@@ -74,7 +74,7 @@ LL |     if let Some(Some(x)) = &mut Some(&mut Some(0)) {
    |                      ~
 
 error[E0308]: mismatched types
-  --> $DIR/ref_pat_eat_one_layer_2021.rs:25:22
+  --> $DIR/ref_pat_eat_one_layer_2021_fail.rs:25:22
    |
 LL |     if let Some(Some(&x)) = &Some(&Some(0)) {
    |                      ^^     --------------- this expression has type `&Option<&Option<{integer}>>`
@@ -89,7 +89,7 @@ LL |     if let Some(Some(x)) = &Some(&Some(0)) {
    |                      ~
 
 error[E0308]: mismatched types
-  --> $DIR/ref_pat_eat_one_layer_2021.rs:29:27
+  --> $DIR/ref_pat_eat_one_layer_2021_fail.rs:29:27
    |
 LL |     if let Some(&mut Some(&x)) = &Some(&mut Some(0)) {
    |                           ^^     ------------------- this expression has type `&Option<&mut Option<{integer}>>`
@@ -104,7 +104,7 @@ LL |     if let Some(&mut Some(x)) = &Some(&mut Some(0)) {
    |                           ~
 
 error[E0308]: mismatched types
-  --> $DIR/ref_pat_eat_one_layer_2021.rs:33:23
+  --> $DIR/ref_pat_eat_one_layer_2021_fail.rs:33:23
    |
 LL |     if let Some(&Some(&mut x)) = &mut Some(&Some(0)) {
    |                       ^^^^^^     ------------------- this expression has type `&mut Option<&Option<{integer}>>`
@@ -114,7 +114,7 @@ LL |     if let Some(&Some(&mut x)) = &mut Some(&Some(0)) {
    = note:           expected type `{integer}`
            found mutable reference `&mut _`
 note: to declare a mutable binding use: `mut x`
-  --> $DIR/ref_pat_eat_one_layer_2021.rs:33:23
+  --> $DIR/ref_pat_eat_one_layer_2021_fail.rs:33:23
    |
 LL |     if let Some(&Some(&mut x)) = &mut Some(&Some(0)) {
    |                       ^^^^^^

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024.rs

@@ -63,4 +63,27 @@ pub fn main() {
     if let Some(&mut x) = &Some(&mut 0) {
         let _: &u32 = x;
     }
+
+    fn generic<R: Ref>() -> (R, bool) {
+        R::meow()
+    }
+
+    trait Ref: Sized {
+        fn meow() -> (Self, bool);
+    }
+
+    impl Ref for &'static [(); 0] {
+        fn meow() -> (Self, bool) {
+            (&[], false)
+        }
+    }
+
+    impl Ref for &'static mut [(); 0] {
+        fn meow() -> (Self, bool) {
+            (&mut [], true)
+        }
+    }
+
+    let (&_, b) = generic();
+    assert!(!b);
 }

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_fail.both.stderr

@@ -150,7 +150,20 @@ LL |     let Foo(mut a) = &mut Foo(0);
    = 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 14 previous errors
+error[E0277]: the trait bound `&_: main::Ref` is not satisfied
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:83:14
+   |
+LL |     let &_ = generic();
+   |              ^^^^^^^^^ the trait `main::Ref` is not implemented for `&_`
+   |
+   = help: the trait `main::Ref` is implemented for `&'static mut [(); 0]`
+note: required by a bound in `generic`
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:69:19
+   |
+LL |     fn generic<R: Ref>() -> R {
+   |                   ^^^ required by this bound in `generic`
 
-Some errors have detailed explanations: E0308, E0658.
-For more information about an error, try `rustc --explain E0308`.
+error: aborting due to 15 previous errors
+
+Some errors have detailed explanations: E0277, E0308, E0658.
+For more information about an error, try `rustc --explain E0277`.

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_fail.classic.stderr

@@ -180,7 +180,20 @@ LL |     let Foo(mut a) = &mut Foo(0);
    = 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
+error[E0277]: the trait bound `&_: main::Ref` is not satisfied
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:83:14
+   |
+LL |     let &_ = generic();
+   |              ^^^^^^^^^ the trait `main::Ref` is not implemented for `&_`
+   |
+   = help: the trait `main::Ref` is implemented for `&'static mut [(); 0]`
+note: required by a bound in `generic`
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:69:19
+   |
+LL |     fn generic<R: Ref>() -> R {
+   |                   ^^^ required by this bound in `generic`
 
-Some errors have detailed explanations: E0308, E0658.
-For more information about an error, try `rustc --explain E0308`.
+error: aborting due to 17 previous errors
+
+Some errors have detailed explanations: E0277, E0308, E0658.
+For more information about an error, try `rustc --explain E0277`.

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_fail.rs

@@ -65,4 +65,20 @@ pub fn main() {
     let Foo(mut a) = &mut Foo(0);
     //~^ ERROR: binding cannot be both mutable and by-reference
     a = &mut 42;
+
+    fn generic<R: Ref>() -> R {
+        R::meow()
+    }
+
+    trait Ref: Sized {
+        fn meow() -> Self;
+    }
+
+    impl Ref for &'static mut [(); 0] {
+        fn meow() -> Self {
+            &mut []
+        }
+    }
+
+    let &_ = generic(); //~ERROR: the trait bound `&_: main::Ref` is not satisfied [E0277]
 }

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_fail.structural.stderr

@@ -161,7 +161,20 @@ LL |     let Foo(mut a) = &mut Foo(0);
    = 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 15 previous errors
+error[E0277]: the trait bound `&_: main::Ref` is not satisfied
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:83:14
+   |
+LL |     let &_ = generic();
+   |              ^^^^^^^^^ the trait `main::Ref` is not implemented for `&_`
+   |
+   = help: the trait `main::Ref` is implemented for `&'static mut [(); 0]`
+note: required by a bound in `generic`
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:69:19
+   |
+LL |     fn generic<R: Ref>() -> R {
+   |                   ^^^ required by this bound in `generic`
 
-Some errors have detailed explanations: E0308, E0658.
-For more information about an error, try `rustc --explain E0308`.
+error: aborting due to 16 previous errors
+
+Some errors have detailed explanations: E0277, E0308, E0658.
+For more information about an error, try `rustc --explain E0277`.