[libcxx-commits] [libcxx] [libc++][unique_ptr] Implement LWG 4144: Disallow unique_ptr<T&, D> (PR #209018)

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emmett2020 wrote:

> > Implement [LWG 4144](https://cplusplus.github.io/LWG/issue4144) by explicitly rejecting `unique_ptr<T, D>` when `T*` is not a valid type.
> > This adds a pointability check and tests reference and abominable function types. It also includes a minor formatting cleanup for `unique_ptr`'s `nullptr` comparison operator.
> > Fixes #118359
> 
> Formatting updates are considered unrelated changes usually. If necessary they need to be submitted as NFC separately. Please revert those changes.

Thanks for the review. I've reverted unrelated format changes. 

https://github.com/llvm/llvm-project/pull/209018