Implement standard traits on C-unwind ABI function pointers

[lopopolo]

Proposal

Implement the standard set of core traits on C-unwind ABI function pointers:

• Add default trait implementations for "c-unwind" ABI function pointers rust#101263

Problem statement

I would like to stabilize RFC rust-lang/rfcs#2945 which has tracking Issue rust-lang/rust#74990. Implementing common traits like fmt::Debug on these function pointers is blocking stabilization of the c_unwind feature.

Motivation, use-cases

The lack of common traits like fmt::Debug on C-unwind ABI function pointers prevents them from being used with common tools like bindgen.

Solution sketches

rust-lang/rust#101263 has been filed and signed off on by the compiler team.

Links and related work

• Add default trait implementations for "c-unwind" ABI function pointers rust#101263
• Add default trait implementations for "c-unwind" ABI function pointers rust#101263 (comment)
• Implement Debug, Pointer, etc on function pointers for all calling conventions rust#92964
• builtin trait to abstract over function pointers rust#99531 (comment)

What happens now?

This issue is part of the libs-api team API change proposal process. Once this issue is filed the libs-api team will review open proposals in its weekly meeting. You should receive feedback within a week or two.

[lopopolo]

I was asked to file this ACP by @thomcc here: rust-lang/rust#101263 (comment).

[lopopolo]

Hi folks, checking in on this ACP since its been about 4 weeks since I opened it and the rustc dev guide and ticket template hinted that this would be looked at within a week or two.

This ACP is (I think) blocking the addition of some fmt traits as part of an already accepted RFC. Is there a part of the process I've missed?

I'm still not quite sure why this change (which is part of a larger, already-approved RFC) is blocked on an ACP. It looks like some API changes, like rust-lang/rust#101308, can make it to nightly without one.

@joshtriplett is this ACP something you can help me get some eyes on? (I saw you approved the new API addition I linked)

[lopopolo]

rust-lang/rust#101263 is approved and in the bors queue, which I think means this ACP is not required anymore.