Match ergonomics 2024: test type inference

Author: Jules-Bertholet

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    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date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`
+
+error: aborting due to 15 previous errors
 
-Some errors have detailed explanations: E0308, E0658.
-For more information about an error, try `rustc --explain E0308`.
+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    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date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`
+
+error: aborting due to 17 previous errors
 
-Some errors have detailed explanations: E0308, E0658.
-For more information about an error, try `rustc --explain E0308`.
+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`
+
+error: aborting due to 16 previous errors
 
-Some errors have detailed explanations: E0308, E0658.
-For more information about an error, try `rustc --explain E0308`.
+Some errors have detailed explanations: E0277, E0308, E0658.
+For more information about an error, try `rustc --explain E0277`.