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matklad / once_cell

Rust library for single assignment cells and lazy statics without macros
Apache License 2.0
1.84k stars 110 forks source link

enable some thread-using tests on Miri #112

Closed RalfJung closed 4 years ago

matklad commented 4 years ago

Ah, missed those, thanks!

bors r+

And, as you are going to be bugged by a notification anyway, you might want to look at completely unrelated https://github.com/matklad/once_cell/pull/110/commits/d5295146e2fa80f4e7ad455fd97d21e3002ec885 which exposed an interesting API quirk of MaybeUninit. If you use MaybeUninit, you have to write your Drop impl, which requires an (unstable) may_dangle to be dropck transparent. Am I correct that there's no way to simulate ManyallyDrop + may_dangle on stable, other than just using Option instead of MaybeUninit?

bors[bot] commented 4 years ago

Build succeeded:

RalfJung commented 4 years ago

Presumably you need the Drop impl because the field is not always initialized when the container is dropped -- so even if the UB rules were different and MaybeUninit was not necessary, that still wouldn't help, it would just be wrong to always drop?

Yeah that is an interesting quirk that I have not seen yet. Might be worth bringing up in the rust-lang/rust repo in case it hasn't already.