`vec::IntoIter<T>: UnwindSafe` should not require `T: RefUnwindSafe`

[SabrinaJewson]

Currently, vec::IntoIter<T> is only UnwindSafe if T is RefUnwindSafe. It probably inherits this implementation from NonNull, but I don’t think it makes much sense. I really don’t think you can cause state corruption with a vec::IntoIter<RefCell<T>> in scope for example, since they’d all be dropped.

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rustc --version --verbose:

rustc 1.88.0 (6b00bc388 2025-06-23)
binary: rustc
commit-hash: 6b00bc3880198600130e1cf62b8f8a93494488cc
commit-date: 2025-06-23
host: x86_64-unknown-linux-gnu
release: 1.88.0
LLVM version: 20.1.5

[bjorn3]

Changing the bound to T: UnwindSafe would make sense to me, but I don't know if we can do so in a backwards compatible way.

[SabrinaJewson]

It already requires T: UnwindSafe, so I don’t think it should be a problem.