Tracking issue for const `Pin` methods

[CDirkx]

Constify methods of core::pin::Pin under the feature const_pin.

Implementation: #76655

Methods in const_pin (stable since https://github.com/rust-lang/rust/pull/130136):

• new
• new_unchecked
• get_ref
• into_ref
• get_mut
• get_unchecked_mut
• static_ref
• static_mut

Methods in const_pin2:

• into_inner
• into_inner_unchecked

The const_pin2 methods will need #[rustc_allow_const_fn_unstable(const_precise_live_drops)] but that has been approved here.

[ecstatic-morse]

As you mention in #76655 PR, the implementation of some of these methods depends on the unstable const_precise_live_drops feature. Future readers should check the status of that feature before attempting to stabilize these. #76618 will ensure that this does not happen by accident.

[RalfJung]

@dtolnay wrote

I'd be happy to take a separate PR for the const-stabilizing of into_inner + into_inner_unchecked. Procedurally I think a fresh FCP would be required.

So, let's get that train rolling -- @rust-lang/libs-api can we const-stabilize the const_pin2 feature gate, which guards Pin::into_inner and Pin::into_inner_unchecked (already stable outside const)?

[dtolnay]

@rfcbot fcp merge

[rfcbot]

Team member @dtolnay has proposed to merge this. The next step is review by the rest of the tagged team members:

• [x] @Amanieu
• [x] @BurntSushi
• [x] @dtolnay
• [x] @joshtriplett
• [x] @m-ou-se

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[tgross35]

can we const-stabilize the const_pin2 feature gate, which guards Pin::into_inner and Pin::into_inner_unchecked

Since this will likely be the same release cycle, the const_pin2 items can probably just be grouped back into const_pin.

[tgross35]

@Amanieu @BurntSushi @m-ou-se could this get one more check? So we avoid splitting const_pin if fcp doesn't make the next branch.

[rfcbot]

:bell: This is now entering its final comment period, as per the review above. :bell:

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

[RalfJung]

Stabilization PR is up at https://github.com/rust-lang/rust/pull/133127