Tracking Issue for const_intrinsic_copy

[usbalbin]

Feature gate: #![feature(const_intrinsic_copy)]

This is a tracking issue for making the functions ptr::copy and ptr::copy_nonoverlapping as well as some related functions const fn.

Public API

mod ptr {
    pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
    pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize);
}

impl *const T {
    pub const unsafe fn copy_to(self, dest: *mut T, count: usize);
    pub const unsafe fn copy_to_nonoverlapping(self, dest: *mut T, count: usize);
}

impl *mut T {
    pub const unsafe fn copy_to(self, dest: *mut T, count: usize);
    pub const unsafe fn copy_to_nonoverlapping(self, dest: *mut T, count: usize);

    pub const unsafe fn copy_from(self, src: *const T, count: usize);
    pub const unsafe fn copy_from_nonoverlapping(self, src: *const T, count: usize);
}

Steps / History

• Implementation of ptr::copy and ptr::copy_nonoverlapping as const fn: Make copy[_nonoverlapping] const #79684
  • Link to this issue in feature gate: const_intrinsic_copy - Add Reference to tracking issue #80699
• Also constify copy_to, copy_from and friends : Constify copy related functions #83091
• Final commenting period (FCP)
• Stabilization PR: Stabilize const_intrinsic_copy #97276
• De-stabilization PR: revert stabilization of const_intrinsic_copy #117905
• TODO: new stabilization PR, once Tracking issue for &mut T in const contexts (const_mut_refs) #57349 is stable

[usbalbin]

@RalfJung with #81238 merged, is the concern about "bringing back debug assertions" resolved as - we won't bring them back?

[RalfJung]

Yeah I guess for now we won't bring them back.

[RalfJung]

This got partially reverted again by #86003, but hopefully we can re-land it soon.

[RalfJung]

Sorry, I misread, this feature gate is not affected (but some others are).

[joshtriplett]

Seems reasonable, assuming that @rust-lang/wg-const-eval is fine with it.

@rfcbot merge
@rfcbot concern confirm-with-wg-const-eval

[rfcbot]

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

• @Amanieu
• @BurntSushi
• @dtolnay
• @joshtriplett
• @m-ou-se
• @yaahc

Concerns:

• confirm-with-wg-const-eval resolved by Tracking Issue for const_intrinsic_copy #80697 (comment)

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.

[RalfJung]

Fine from my side -- these are all conceptually simple functions and their implementation has been battle-tested a lot in Miri.

[joshtriplett]

@rfcbot resolve confirm-with-wg-const-eval