Tracking Issue for `#[track_caller]` on closures

[Aaron1011]

This is a tracking issue for the RFC "XXX" (rust-lang/rfcs#NNN).
The feature gate for the issue is #![feature(closure_track_caller)].

About tracking issues

Tracking issues are used to record the overall progress of implementation.
They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions.
A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.

Steps

• Implement the RFC
• Adjust documentation (see instructions on rustc-dev-guide)
• Stabilization PR (see instructions on rustc-dev-guide)

Unresolved Questions

XXX --- list all the "unresolved questions" found in the RFC to ensure they are
not forgotten

• Should async {}, etc support track caller on their lowered closures?

Implementation history

• Initial implementation in Support #[track_caller] on closures and generators #87064

[kartva]

What's the status of this issue? I'd be happy to try and pursue stabilization if it's ready.

[Aaron1011]

Even if this is stabilized, you'll still need the unstable stmt_expr_attributes to actually write it on a closure expression: #15701

[mpfaff]

Even if this is stabilized, you'll still need the unstable stmt_expr_attributes to actually write it on a closure expression: #15701

That seems to be the case only if the closure is not passed immediately as a function argument:

// This works
let x = std::convert::identity(#[track_caller] || {});
// But this does not
let x = #[track_caller] || {};

Maybe I'm misunderstanding the terminology, but in the case that does work, the closure is still an expression, no?

[Aaron1011]

You're right - this seems like a bug in the stmt_expr_attributes feature gate (or maybe an intentional partial stabilization).