Rollup merge of #65977 - ohadravid:fix-incorrect-diagnostics-with-an-associated-type, r=estebank

Fix incorrect diagnostics for expected type in E0271 with an associated type

With code like the following code:

```rust
#[derive(Debug)]
struct Data {}

fn do_stuff<'a>(iterator: impl Iterator<Item = &'a Data>) {
    for item in iterator {
        println!("{:?}", item)
    }
}

fn main() {
    let v = vec![Data {}];

    do_stuff(v.into_iter());
}
```

the diagnostic (in nightly & stable) wrongly complains about the expected type:

```
error[E0271]: type mismatch resolving `<std::vec::IntoIter<Data> as std::iter::Iterator>::Item == &Data`
  --> src/main.rs:15:5
   |
5  | fn do_stuff<'a>(iterator: impl Iterator<Item = &'a Data>) {
   |    --------                             --------------- required by this bound in `do_stuff`
...
15 |     do_stuff(v.into_iter());
   |     ^^^^^^^^ expected struct `Data`, found &Data
   |
   = note: expected type `Data`
              found type `&Data`
```

This PR fixes this issue by flipping the expected/actual values where appropriate, so it looks like this:

```
error[E0271]: type mismatch resolving `<std::vec::IntoIter<Data> as std::iter::Iterator>::Item == &Data`
  --> main.rs:15:5
   |
5  | fn do_stuff<'a>(iterator: impl Iterator<Item = &'a Data>) {
   |    --------                             --------------- required by this bound in `do_stuff`
...
15 |     do_stuff(v.into_iter());
   |     ^^^^^^^^ expected &Data, found struct `Data`
   |
   = note: expected type `&Data`
              found type `Data`
```

This improves the output of a lot of existing tests (check out `associated-types-binding-to-type-defined-in-supertrait`!).

The only change which I wasn't too sure about is in the test `associated-types-overridden-binding-2`, but I think it's an improvement and the underlying problem is with handling of `trait_alias`.

Fix #57226, fix #64760, fix #58092.

0 files changed, 0 insertions, 0 deletions