Make NonZero<char> possible

[hkBst]

I'd like to use NonZero<char> for representing units of CStr in https://github.com/rust-lang/literal-escaper

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[hanna-kruppe]

It’s not clear from the diff, but I guess since NonZero<T> works by trait impls on T, this can’t be feature-gated and would immediately allow NonZero<char> on stable?

[jieyouxu]

r? libs-api

[hkBst]

It’s not clear from the diff, but I guess since NonZero<T> works by trait impls on T, this can’t be feature-gated and would immediately allow NonZero<char> on stable?

That's a good point I hadn't considered. I'll look into whether a feature gate is possible.

[tgross35]

Could you add a test so we don't accidentally regress this? library/coretests/tests/num/niche_types.rs doesn't exist yet but probably would be the place.

[hkBst]

Could you add a test so we don't accidentally regress this? library/coretests/tests/num/niche_types.rs doesn't exist yet but probably would be the place.

Do you mean a test that just uses all the possible NonZero-able types as NonZeros? Meaning they are tested for being possible. Or is there another thing you meant?

[tgross35]

I did only mean something to check basic usage of the type, and was only thinking of char since the other types are covered by the NonZeroUxx doctests. It wouldn't be bad to just add the same kind of test for all the types, though.