Extend ptr::null and null_mut to all thin (including extern) types by SimonSapin...
source link: https://github.com/rust-lang/rust/pull/94954
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Contributor
SimonSapin
commented
on Mar 15
Fixes #93959
This change was accepted in https://rust-lang.github.io/rfcs/2580-ptr-meta.html
Note that this changes the signature of stable functions. The change should be backward-compatible, but it is insta-stable since it cannot (easily, at all?) be made available only through a #![feature(…)] opt-in.
The RFC also proposed the same change for NonNull::dangling, which makes sense it terms of its signature but not in terms of its implementation. dangling uses align_of() as an address. But what align_of() should be for extern types or whether it should be allowed at all remains an open question.
This commit depends on #93977, which is not yet part of the bootstrap compiler. So #[cfg] is used to only apply the change in stage 1+. As far a I know bounds cannot be made conditional with #[cfg], so the entire functions are duplicated. This is unfortunate but temporary.
Since this duplication makes it less obvious in the diff, the new definitions differ in:
- More permissive bounds (
Thininstead of impliedSized) - Different implementation
- Having
rustc_allow_const_fn_unstable(const_fn_trait_bound) - Having
rustc_allow_const_fn_unstable(ptr_metadata)
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