Rollup merge of #138514 - compiler-errors:fake-borrow-ref-to-value, r=oli-obk

Remove fake borrows of refs that are converted into non-refs in `MakeByMoveBody`

Remove fake borrows of closure captures if that capture has been replaced with a by-move version of that capture.

For example, given an async closure that looks like:

```
let f: Foo;
let c = async move || {
    match f { ... }
};
```

... in this pair of coroutine-closure + coroutine, we capture `Foo` in the parent and `&Foo` in the child. We will emit two fake borrows like:

```
_2 = &fake shallow (*(_1.0: &Foo));
_3 = &fake shallow (_1.0: &Foo);
```

However, since the by-move-body transform is responsible for replacing `_1.0: &Foo` with `_1.0: Foo` (since the `AsyncFnOnce` coroutine will own `Foo` by value), that makes the second fake borrow obsolete since we never have an upvar of type `&Foo`, and we should replace it with a `nop`.

As a side-note, we don't actually even care about fake borrows here at all since they're fully a MIR borrowck artifact, and we don't need to borrowck by-move MIR bodies. But it's best to preserve as much as we can between these two bodies :)

Fixes #138501

r? oli-obk

0 files changed, 0 insertions, 0 deletions