Missing tests for #92630

[steffahn]

Right.. #92630 is my own PR; I'm noting this as an issue, mainly so I won't forget this, because I won't do this myself right now / today. Or someone else can do this if they want.

I'm not 100% certain where the best place for such a test to go is, and/or whether it makes sense to have them in one place or separated and more close to the respective type's definition.

A test to prevent any future regression removing the new auto trait implementations introduced by #92630 can look about as follows

// does not need to run, just tests by whether or not this compiles
fn _test<'a>() {
    use std::marker::PhantomData;
    use std::panic::{RefUnwindSafe, UnwindSafe};

    trait Trait {}
    type NoAutoTraits<'a> = PhantomData<dyn Trait + 'a>;
    fn all_auto_traits<T: Send + Sync + Unpin + UnwindSafe + RefUnwindSafe>() {}

    all_auto_traits::<std::iter::Empty<NoAutoTraits<'a>>>();
    all_auto_traits::<std::hash::BuildHasherDefault<NoAutoTraits<'a>>>();
    all_auto_traits::<std::future::Pending<NoAutoTraits<'a>>>();
}

Edit: This code is needlessly complicated, see my comment below.

@rustbot label C-enhancement, A-testsuite, E-easy, E-needs-test, T-libs

[tamaroning]

@rustbot claim

[steffahn]

@tamaroning

FYI, somehow I missed the more straightforward way of writing these.

// does not need to run, just tests by whether or not this compiles
fn _test<T>() {
    use std::panic::{RefUnwindSafe, UnwindSafe};

    fn all_auto_traits<T: Send + Sync + Unpin + UnwindSafe + RefUnwindSafe>() {}

    all_auto_traits::<std::iter::Empty<T>>();
    all_auto_traits::<std::hash::BuildHasherDefault<T>>();
    all_auto_traits::<std::future::Pending<T>>();
}