Re-export f16 and f128 into core::primitive.

[bjoernager]

Tracking issue: #116909.

This PR re-exports f16 and f128 into core::primitive.

IIRC we already have unstable re-exports in other places of the standard library.

C.c. @joseluis.

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[bjoernager]

@rustbot label +T-libs-api -T-libs

r? libs-api

[dtolnay]

Thanks!

View changes since this review

[dtolnay]

@bors r+

[bors]

📌 Commit 3981f98 has been approved by dtolnay

It is now in the queue for this repository.

[tgross35]

Did you double check that this doesn't allow escaping the feature gates? That was the reason we didn't do this at one point #116909 (comment)

[bjoernager]

I assumed that this would behave like the unstable re-exports that we already have (from a quick search I can find BorrowedBuf as one example). I did verify those, but not this one directly, no.

[dtolnay]

Yeah, sure enough. Good catch. This surprisingly compiles:

use core::primitive::f16;

fn main() {
    let _: f16;
}

It would be good to instead add a placeholder comment in library/core/src/primitive.rs indicating that we know we want this re-export but cannot have it until the type is stable (or the stability checking is fixed).

@bors r-

[bjoernager]

I suppose that this will have to wait in the meantime.