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Auto merge of #89633 - rhysd:issue-65230, r=petrochenkov

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Show detailed expected/found types in error message when trait paths are the same

Fixes #65230.

### Issue solved by this PR

```rust
trait T {
    type U;
    fn f(&self) -> Self::U;
}

struct X<'a>(&'a mut i32);

impl<'a> T for X<'a> {
    type U = &'a i32;
    fn f(&self) -> Self::U {
        self.0
    }
}

fn main() {}
```

Compiler generates the following note:

```
note: ...so that the types are compatible
  --> test.rs:10:28
   |
10 |       fn f(&self) -> Self::U {
   |  ____________________________^
11 | |         self.0
12 | |     }
   | |_____^
   = note: expected `T`
              found `T`
```

This note is not useful since the expected type and the found type are the same.

### How this PR solve the issue

When the expected type and the found type are exactly the same in string representation, the note falls back to the detailed string representation of trait ref:

```
note: ...so that the types are compatible
  --> test.rs:10:28
   |
10 |       fn f(&self) -> Self::U {
   |  ____________________________^
11 | |         self.0
12 | |     }
   | |_____^
   = note: expected `<X<'a> as T>`
              found `<X<'_> as T>`
```

So that a user can notice what was different between the expected one and the found one.
This commit is contained in:
bors 2021-10-10 15:59:28 +00:00
commit 68dfa07e3b
9 changed files with 59 additions and 20 deletions
Download patch file Download diff file Expand all files Collapse all files

14
compiler/rustc_infer/src/infer/error_reporting/mod.rs
View file

@ -2060,14 +2060,24 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
expected: exp_found.expected.print_only_trait_path(),
found: exp_found.found.print_only_trait_path(),
};
self.expected_found_str(pretty_exp_found)
match self.expected_found_str(pretty_exp_found) {
Some((expected, found)) if expected == found => {
self.expected_found_str(exp_found)
}
ret => ret,
}
}
infer::PolyTraitRefs(exp_found) => {
let pretty_exp_found = ty::error::ExpectedFound {
expected: exp_found.expected.print_only_trait_path(),
found: exp_found.found.print_only_trait_path(),
};
self.expected_found_str(pretty_exp_found)
match self.expected_found_str(pretty_exp_found) {
Some((expected, found)) if expected == found => {
self.expected_found_str(exp_found)
}
ret => ret,
}
}
}
}

4
src/test/ui/error-codes/E0308-2.stderr
View file

@ -4,8 +4,8 @@ error[E0308]: mismatched types
LL | impl Eq for &dyn DynEq {}
| ^^ lifetime mismatch
|
= note: expected trait `PartialEq`
found trait `PartialEq`
= note: expected trait `<&dyn DynEq as PartialEq>`
found trait `<&(dyn DynEq + 'static) as PartialEq>`
note: the lifetime `'_` as defined on the impl at 9:13...
--> $DIR/E0308-2.rs:9:13
|

4
src/test/ui/issues/issue-20831-debruijn.stderr
View file

@ -19,8 +19,8 @@ note: ...so that the types are compatible
|
LL | fn subscribe(&mut self, t : Box<dyn Subscriber<Input=<Self as Publisher>::Output> + 'a>) {
| ^^^^^^^^^
= note: expected `Publisher<'_>`
found `Publisher<'_>`
= note: expected `<MyStruct<'a> as Publisher<'_>>`
found `<MyStruct<'_> as Publisher<'_>>`
error: aborting due to previous error

11
src/test/ui/issues/issue-65230.rs Normal file
View file

@ -0,0 +1,11 @@
trait T0 {}
trait T1: T0 {}
trait T2 {}
impl<'a> T0 for &'a (dyn T2 + 'static) {}
impl T1 for &dyn T2 {}
//~^ ERROR mismatched types
fn main() {}

18
src/test/ui/issues/issue-65230.stderr Normal file
View file

@ -0,0 +1,18 @@
error[E0308]: mismatched types
--> $DIR/issue-65230.rs:8:6
|
LL | impl T1 for &dyn T2 {}
| ^^ lifetime mismatch
|
= note: expected trait `<&dyn T2 as T0>`
found trait `<&(dyn T2 + 'static) as T0>`
note: the lifetime `'_` as defined on the impl at 8:13...
--> $DIR/issue-65230.rs:8:13
|
LL | impl T1 for &dyn T2 {}
| ^
= note: ...does not necessarily outlive the static lifetime
error: aborting due to previous error
For more information about this error, try `rustc --explain E0308`.

4
src/test/ui/nll/issue-50716.stderr
View file

@ -4,8 +4,8 @@ error[E0308]: mismatched types
LL | let _x = *s;
| ^^ lifetime mismatch
|
= note: expected type `Sized`
found type `Sized`
= note: expected type `<<&'a T as A>::X as Sized>`
found type `<<&'static T as A>::X as Sized>`
note: the lifetime `'a` as defined on the function body at 9:8...
--> $DIR/issue-50716.rs:9:8
|

8
src/test/ui/variance/variance-contravariant-self-trait-match.stderr
View file

@ -4,8 +4,8 @@ error[E0308]: mismatched types
LL | impls_get::<&'min G>();
| ^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
|
= note: expected type `Get`
found type `Get`
= note: expected type `<&'min G as Get>`
found type `<&'max G as Get>`
note: the lifetime `'min` as defined on the function body at 10:21...
--> $DIR/variance-contravariant-self-trait-match.rs:10:21
|
@ -23,8 +23,8 @@ error[E0308]: mismatched types
LL | impls_get::<&'max G>();
| ^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
|
= note: expected type `Get`
found type `Get`
= note: expected type `<&'max G as Get>`
found type `<&'min G as Get>`
note: the lifetime `'min` as defined on the function body at 16:21...
--> $DIR/variance-contravariant-self-trait-match.rs:16:21
|

8
src/test/ui/variance/variance-covariant-self-trait-match.stderr
View file

@ -4,8 +4,8 @@ error[E0308]: mismatched types
LL | impls_get::<&'min G>();
| ^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
|
= note: expected type `Get`
found type `Get`
= note: expected type `<&'min G as Get>`
found type `<&'max G as Get>`
note: the lifetime `'min` as defined on the function body at 10:21...
--> $DIR/variance-covariant-self-trait-match.rs:10:21
|
@ -23,8 +23,8 @@ error[E0308]: mismatched types
LL | impls_get::<&'max G>();
| ^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
|
= note: expected type `Get`
found type `Get`
= note: expected type `<&'max G as Get>`
found type `<&'min G as Get>`
note: the lifetime `'min` as defined on the function body at 17:21...
--> $DIR/variance-covariant-self-trait-match.rs:17:21
|

8
src/test/ui/variance/variance-invariant-self-trait-match.stderr
View file

@ -4,8 +4,8 @@ error[E0308]: mismatched types
LL | impls_get::<&'min G>();
| ^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
|
= note: expected type `Get`
found type `Get`
= note: expected type `<&'min G as Get>`
found type `<&'max G as Get>`
note: the lifetime `'min` as defined on the function body at 7:21...
--> $DIR/variance-invariant-self-trait-match.rs:7:21
|
@ -23,8 +23,8 @@ error[E0308]: mismatched types
LL | impls_get::<&'max G>();
| ^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
|
= note: expected type `Get`
found type `Get`
= note: expected type `<&'max G as Get>`
found type `<&'min G as Get>`
note: the lifetime `'min` as defined on the function body at 13:21...
--> $DIR/variance-invariant-self-trait-match.rs:13:21
|