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When a trait isn't implemented, but another similar impl is found, point at it #145640

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error[E0277]: the trait bound `u32: Trait` is not satisfied
  --> $DIR/trait_objects_fail.rs:26:9
   |
LL |     foo(&10_u32);
   |         ^^^^^^^ the trait `Trait` is not implemented for `u32`
   |
help: the trait `Trait<12>` is not implemented for `u32`
      but trait `Trait<2>` is implemented for it
  --> $DIR/trait_objects_fail.rs:7:1
   |
LL | impl Trait<2> for u32 {}
   | ^^^^^^^^^^^^^^^^^^^^^
   = note: required for the cast from `&u32` to `&dyn Trait`

Pointing at the impl definition that could apply given a different self type is particularly useful when it has a blanket self type, as it might not be obvious and is not trivially greppable:

error[E0277]: the trait bound `RawImpl<_>: Raw<_>` is not satisfied
  --> $DIR/issue-62742.rs:4:5
   |
LL |     WrongImpl::foo(0i32);
   |     ^^^^^^^^^ unsatisfied trait bound
   |
help: the trait `Raw<_>` is not implemented for `RawImpl<_>`
      but trait `Raw<[_]>` is implemented for it
  --> $DIR/issue-62742.rs:29:1
   |
LL | impl<T> Raw<[T]> for RawImpl<T> {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: required by a bound in `SafeImpl`
  --> $DIR/issue-62742.rs:33:35
   |
LL | pub struct SafeImpl<T: ?Sized, A: Raw<T>>(PhantomData<(A, T)>);
   |                                   ^^^^^^ required by this bound in `SafeImpl`

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rustbot commented Aug 20, 2025

r? @nnethercote

rustbot has assigned @nnethercote.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Aug 20, 2025
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rustbot commented Aug 20, 2025

rustc_errors::emitter was changed

cc @Muscraft

This PR modifies tests/ui/issues/. If this PR is adding new tests to tests/ui/issues/,
please refrain from doing so, and instead add it to more descriptive subdirectories.

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@estebank estebank force-pushed the point-at-impl-e0277 branch from 3967b4e to c6c62f4 Compare August 20, 2025 17:59
@rustbot rustbot added the WG-trait-system-refactor The Rustc Trait System Refactor Initiative (-Znext-solver) label Aug 20, 2025
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Looks fine, r=me once everything is green.

@nnethercote nnethercote added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 22, 2025
@estebank estebank force-pushed the point-at-impl-e0277 branch from c6c62f4 to a05bf52 Compare August 22, 2025 18:59
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@estebank estebank force-pushed the point-at-impl-e0277 branch from a05bf52 to 3f07cda Compare August 23, 2025 16:12
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@bors r=nnethercote

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bors commented Aug 23, 2025

📌 Commit 3f07cda has been approved by nnethercote

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Aug 23, 2025
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jhpratt commented Aug 23, 2025

@bors r- (has merge conflicts)

@bors bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Aug 23, 2025
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bors commented Aug 24, 2025

☔ The latest upstream changes (presumably #145706) made this pull request unmergeable. Please resolve the merge conflicts.

@estebank estebank force-pushed the point-at-impl-e0277 branch from 3f07cda to 898ddc3 Compare August 24, 2025 16:55
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@bors r=nnethercote rollup=never

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bors commented Aug 24, 2025

📌 Commit 898ddc3 has been approved by nnethercote

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Aug 24, 2025
bors added a commit that referenced this pull request Aug 25, 2025
@bors
Auto merge of #145640 - estebank:point-at-impl-e0277, r=nnethercote
6bdc49a 
When a trait isn't implemented, but another similar impl is found, point at it

```
error[E0277]: the trait bound `u32: Trait` is not satisfied
  --> $DIR/trait_objects_fail.rs:26:9
   |
LL |     foo(&10_u32);
   |         ^^^^^^^ the trait `Trait` is not implemented for `u32`
   |
help: the trait `Trait<12>` is not implemented for `u32`
      but trait `Trait<2>` is implemented for it
  --> $DIR/trait_objects_fail.rs:7:1
   |
LL | impl Trait<2> for u32 {}
   | ^^^^^^^^^^^^^^^^^^^^^
   = note: required for the cast from `&u32` to `&dyn Trait`
```

Pointing at the `impl` definition that *could* apply given a different self type is *particularly* useful when it has a blanket self type, as it might not be obvious and is not trivially greppable:

```
error[E0277]: the trait bound `RawImpl<_>: Raw<_>` is not satisfied
  --> $DIR/issue-62742.rs:4:5
   |
LL |     WrongImpl::foo(0i32);
   |     ^^^^^^^^^ unsatisfied trait bound
   |
help: the trait `Raw<_>` is not implemented for `RawImpl<_>`
      but trait `Raw<[_]>` is implemented for it
  --> $DIR/issue-62742.rs:29:1
   |
LL | impl<T> Raw<[T]> for RawImpl<T> {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: required by a bound in `SafeImpl`
  --> $DIR/issue-62742.rs:33:35
   |
LL | pub struct SafeImpl<T: ?Sized, A: Raw<T>>(PhantomData<(A, T)>);
   |                                   ^^^^^^ required by this bound in `SafeImpl`
```
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bors commented Aug 25, 2025

⌛ Testing commit 898ddc3 with merge 6bdc49a...

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bors commented Aug 25, 2025

💔 Test failed - checks-actions

@bors bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Aug 25, 2025
@estebank estebank force-pushed the point-at-impl-e0277 branch from 898ddc3 to c22331f Compare August 25, 2025 15:32
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@bors r=nnethercote

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bors commented Aug 25, 2025

📌 Commit c22331f has been approved by nnethercote

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 25, 2025
bors added a commit that referenced this pull request Aug 25, 2025
@bors
Auto merge of #145640 - estebank:point-at-impl-e0277, r=nnethercote
85abb89 
When a trait isn't implemented, but another similar impl is found, point at it

```
error[E0277]: the trait bound `u32: Trait` is not satisfied
  --> $DIR/trait_objects_fail.rs:26:9
   |
LL |     foo(&10_u32);
   |         ^^^^^^^ the trait `Trait` is not implemented for `u32`
   |
help: the trait `Trait<12>` is not implemented for `u32`
      but trait `Trait<2>` is implemented for it
  --> $DIR/trait_objects_fail.rs:7:1
   |
LL | impl Trait<2> for u32 {}
   | ^^^^^^^^^^^^^^^^^^^^^
   = note: required for the cast from `&u32` to `&dyn Trait`
```

Pointing at the `impl` definition that *could* apply given a different self type is *particularly* useful when it has a blanket self type, as it might not be obvious and is not trivially greppable:

```
error[E0277]: the trait bound `RawImpl<_>: Raw<_>` is not satisfied
  --> $DIR/issue-62742.rs:4:5
   |
LL |     WrongImpl::foo(0i32);
   |     ^^^^^^^^^ unsatisfied trait bound
   |
help: the trait `Raw<_>` is not implemented for `RawImpl<_>`
      but trait `Raw<[_]>` is implemented for it
  --> $DIR/issue-62742.rs:29:1
   |
LL | impl<T> Raw<[T]> for RawImpl<T> {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: required by a bound in `SafeImpl`
  --> $DIR/issue-62742.rs:33:35
   |
LL | pub struct SafeImpl<T: ?Sized, A: Raw<T>>(PhantomData<(A, T)>);
   |                                   ^^^^^^ required by this bound in `SafeImpl`
```
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bors commented Aug 25, 2025

⌛ Testing commit c22331f with merge 85abb89...

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bors commented Aug 25, 2025

💔 Test failed - checks-actions

@bors bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Aug 25, 2025
@nnethercote nnethercote added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 28, 2025
@estebank
When a trait isn't implemented, but another similar impl is found, po…
c7915e8 
…int at it:

```
error[E0277]: the trait bound `u32: Trait` is not satisfied
  --> $DIR/trait_objects_fail.rs:26:9
   |
LL |     foo(&10_u32);
   |         ^^^^^^^ the trait `Trait` is not implemented for `u32`
   |
help: the trait `Trait<12>` is not implemented for `u32`
      but trait `Trait<2>` is implemented for it
  --> $DIR/trait_objects_fail.rs:7:1
   |
LL | impl Trait<2> for u32 {}
   | ^^^^^^^^^^^^^^^^^^^^^
   = note: required for the cast from `&u32` to `&dyn Trait`
```

Pointing at the `impl` definition that *could* apply given a different self type is particularly useful when it has a blanket self type, as it might not be obvious and is not trivially greppable:

```
error[E0277]: the trait bound `RawImpl<_>: Raw<_>` is not satisfied
  --> $DIR/issue-62742.rs:4:5
   |
LL |     WrongImpl::foo(0i32);
   |     ^^^^^^^^^ unsatisfied trait bound
   |
help: the trait `Raw<_>` is not implemented for `RawImpl<_>`
      but trait `Raw<[_]>` is implemented for it
  --> $DIR/issue-62742.rs:29:1
   |
LL | impl<T> Raw<[T]> for RawImpl<T> {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: required by a bound in `SafeImpl`
  --> $DIR/issue-62742.rs:33:35
   |
LL | pub struct SafeImpl<T: ?Sized, A: Raw<T>>(PhantomData<(A, T)>);
   |                                   ^^^^^^ required by this bound in `SafeImpl`
```
@estebank
When more than a single impl and less than 4 could apply, point at …
473078e 
…them

```
error[E0277]: the trait bound `[[u16; 3]; 2]: Bar` is not satisfied
  --> $DIR/issue-67185-2.rs:21:6
   |
LL | impl Foo for FooImpl {}
   |      ^^^ the trait `Bar` is not implemented for `[[u16; 3]; 2]`
   |
help: the following other types implement trait `Bar`
  --> $DIR/issue-67185-2.rs:9:1
   |
LL | impl Bar for [u16; 4] {}
   | ^^^^^^^^^^^^^^^^^^^^^ `[u16; 4]`
LL | impl Bar for [[u16; 3]; 3] {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ `[[u16; 3]; 3]`
note: required by a bound in `Foo`
  --> $DIR/issue-67185-2.rs:14:30
   |
LL | trait Foo
   |       --- required by a bound in this trait
LL | where
LL |     [<u8 as Baz>::Quaks; 2]: Bar,
   |                              ^^^ required by this bound in `Foo`
```
@estebank estebank force-pushed the point-at-impl-e0277 branch from c22331f to 473078e Compare August 28, 2025 16:11
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rustbot commented Aug 28, 2025

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

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