fix: avoid panic in malformed async closures

[YUZHEthefool]

I don’t know why formatting swallows my ai translated content marked with <> :(
So I express the repair content in my own words:
Original implementation skipped the number of parameters capture . So I fix to determine capture ownership based on the binding owner.

Fix: #22821

[ChayimFriedman2]

I don’t know why formatting swallows my ai translated content marked with <>

Probably GitHub got confused thinking they're HTML tags. You can replace them with < and >.

[ChayimFriedman2]

This code is copied from rustc so I heavily doubt it's where the bug is. The bug is probably is some other code that this code consumes its output.

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[rustbot]

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.

[YUZHEthefool]

I found synthetic moves (e.g. let b = b;) in async closure lowering cause HIR paths (resolved by name only) to mismatch formal bindings, breaking child capture vs num_args check.Maybe this is the root cause of the problem.

[ChayimFriedman2]

No, the code is still incorrect. The synthetic names should be there.

View changes since this review

[YUZHEthefool]

Paths generated by async closure lowering can only be resolved by name and hygiene. When parameters have the same name, the generated let b = b may resolve to the wrong binding, destroying the parameter order of coroutine capture.
Im not sure if this is the real way,maybe I should think about this tomorrow

[ChayimFriedman2]

No, let b = b shadows an existing b and resolves to it. This is normal in Rust.

[YUZHEthefool]

Now it only creates internal unique names for subsequent conflicting parameters when rust-analyzer performs error recovery on illegal duplicate async-closure parameters to avoid capture/type inference panics due to misaligned binding identities.
I did confuse the issue in yesterday's commit.