Auto merge of #117661 - TheLazyDutchman:point_out_shadowed_associated_types, r=petrochenkov

Browse source

Added shadowed hint for overlapping associated types

Previously, when you tried to set an associated type that is shadowed by an associated type in a subtrait, like this:

```rust
trait A {
    type X;
}

trait B: A {
    type X; // note: this is legal
}

impl<Y> Clone for Box<dyn B<X=Y, X=Y>> {
    fn clone(&self) -> Self {
        todo!()
    }
}

you got a confusing error message, that says nothing about the shadowing:

error[E0719]: the value of the associated type `X` (from trait `B`) is already specified
 --> test.rs:9:34
  |
9 | impl<Y> Clone for Box<dyn B<X=Y, X=Y>> {
  |                             ---  ^^^ re-bound here
  |                             |
  |                             `X` bound here first

error[E0191]: the value of the associated type `X` (from trait `A`) must be specified
 --> test.rs:9:27
  |
2 |     type X;
  |     ------ `X` defined here
...
9 | impl<Y> Clone for Box<dyn B<X=Y, X=Y>> {
  |                           ^^^^^^^^^^^ help: specify the associated type: `B<X=Y, X=Y, X = Type>`

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0191, E0719.
For more information about an error, try `rustc --explain E0191`.
```

Now instead, the error shows that the associated type is shadowed, and suggests renaming as a potential fix.

```rust
error[E0719]: the value of the associated type `X` in trait `B` is already specified
 --> test.rs:9:34
  |
9 | impl<Y> Clone for Box<dyn B<X=Y, X=Y>> {
  |                             ---  ^^^ re-bound here
  |                             |
  |                             `X` bound here first

error[E0191]: the value of the associated type `X` in `A` must be specified
 --> test.rs:9:27
  |
2 |     type X;
  |     ------ `A::X` defined here
...
6 |     type X; // note: this is legal
  |     ------ `A::X` shadowed here
...
9 | impl<Y> Clone for Box<dyn B<X=Y, X=Y>> {
  |                           ^^^^^^^^^^^ associated type `X` must be specified
  |
help: consider renaming this associated type
 --> test.rs:2:5
  |
2 |     type X;
  |     ^^^^^^
help: consider renaming this associated type
 --> test.rs:6:5
  |
6 |     type X; // note: this is legal
  |     ^^^^^^
```

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0191, E0719.
For more information about an error, try `rustc --explain E0191`.

The rename help message is only emitted when the trait is local. This is true both for the supertrait as for the subtrait.

There might be cases where you can use the fully qualified path (for instance, in a where clause), but this PR currently does not deal with that.

fixes #100109

(continues from #117642, because I didn't know renaming the branch would close the PR)

...

This commit is contained in:

bors 2023-12-06 10:59:24 +00:00

parent 1d2db92987 e550422130

commit 1064316e72

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Show stats Download patch file Download diff file Expand all files Collapse all files

Diff content is not available