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Stabilize const ptr::write* and mem::replace #130954

Merged
merged 3 commits into from
Oct 12, 2024
Merged

Stabilize const ptr::write* and mem::replace #130954

merged 3 commits into from
Oct 12, 2024

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@workingjubilee workingjubilee commented Sep 27, 2024 •
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Since const_mut_refs and const_refs_to_cell have been stabilized, we may now also stabilize the ability to write to places during const evaluation inside our library API. So, we now propose the const fn version of ptr::write and its variants. This allows us to also stabilize mem::replace and ptr::replace.

Their implementation requires an additional internal stabilization of const_intrinsic_forget, which is required for *::write* and thus *::replace. Thus we const-stabilize the internal intrinsics forget, write_bytes, and write_via_move.

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rustbot commented Sep 27, 2024

r? @Mark-Simulacrum

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@rustbot rustbot added A-testsuite Area: The testsuite used to check the correctness of rustc S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-bootstrap Relevant to the bootstrap subteam: Rust's build system (x.py and src/bootstrap) T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Sep 27, 2024
@workingjubilee workingjubilee changed the title Stabilize Stabilize const_mut_refs-dependent API Sep 27, 2024
@workingjubilee workingjubilee added the S-waiting-on-fcp Status: PR is in FCP and is awaiting for FCP to complete. label Sep 27, 2024
@workingjubilee workingjubilee changed the title Stabilize const_mut_refs-dependent API Stabilize 7 const_mut_refs-dependent API Sep 27, 2024
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Note that because the replace stabilization requires the write stabilization in its current implementation, these cannot really land sooner than "all together" even though mem::replace entered FCP earlier, on the 21st.

Also note that there are already existing PRs for most of the slice-related API, so I did not attempt to include any of them except the one that can be expressed via slice syntax: the rest have even harsher dependency orderings.

I will revise this PR appropriately if any of the FCPs garners objections.

@workingjubilee workingjubilee added F-const_mut_refs `#![feature(const_mut_refs)]` WG-const-eval Working group: Const evaluation F-const_refs_to_cell `#[feature(const_refs_to_cell)]` T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. A-const-fn Area: const fn foo(..) {..}. Pure functions which can be applied at compile time. A-const-eval Area: Constant evaluation (MIR interpretation) and removed T-libs Relevant to the library team, which will review and decide on the PR/issue. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-bootstrap Relevant to the bootstrap subteam: Rust's build system (x.py and src/bootstrap) labels Sep 27, 2024
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workingjubilee commented Sep 27, 2024 •
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cc @rust-lang/wg-const-eval As described in the PR message, the const_intrinsic_forget stabilization is part of the dependency chain for const_ptr_write and thus const_replace, and I believe this requires your approval. It's internal-only so it should not exactly be a big deal here.

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RalfJung commented Sep 28, 2024 •
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There's in fact 3 intrinsics marked as const-stable here (meaning they are indirectly exposed to stable const code), which needs wg-const-eval approval, and t-lang should be in the loop as well:

  • forget
  • write_via_move
  • write_bytes

None of them do anything odd. In fact forget does nothing at all; the other two just copy some bytes around -- basic stuff we can confidently commit const-eval to support. The implementation of these has been battle-tested in Miri.

@rust-lang/lang this should be an easy one.

@RalfJung RalfJung added the I-lang-nominated Nominated for discussion during a lang team meeting. label Sep 28, 2024
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Ah, I figured the const_ptr_write ones went without saying.

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It's not clear at all from the stable library surface whether new intrinsics are involved. :)

@workingjubilee workingjubilee added the I-lang-easy-decision Issue: The decision needed by the team is conjectured to be easy. label Sep 28, 2024
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bors commented Sep 28, 2024

☔ The latest upstream changes (presumably #130964) made this pull request unmergeable. Please resolve the merge conflicts.

@workingjubilee workingjubilee force-pushed the stabilize-const-mut-fn branch 2 times, most recently from a377b36 to 5f72cba Compare September 28, 2024 19:02
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@workingjubilee is there a reason #111774 is not included in this PR?

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@rustbot labels -I-lang-nominated

We discussed this in the meeting today... and it's now in FCP.

@rustbot rustbot removed the I-lang-nominated Nominated for discussion during a lang team meeting. label Oct 2, 2024
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workingjubilee commented Oct 2, 2024 •
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Pursuant to my original remarks about modifying this PR if necessary as the FCPs it depends on develops, and to @tgross35's concern, I am going to chop this down to "stabilizations that depend on this T-lang FCP" and extract the quotient into a new PR: #131177

@workingjubilee workingjubilee changed the title Stabilize 7 const_mut_refs-dependent API Stabilize const ptr::write* and mem::replace Oct 2, 2024
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bors commented Oct 5, 2024

☔ The latest upstream changes (presumably #131269) made this pull request unmergeable. Please resolve the merge conflicts.

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bors commented Oct 5, 2024

☔ The latest upstream changes (presumably #131275) made this pull request unmergeable. Please resolve the merge conflicts.

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bors commented Oct 12, 2024

☔ The latest upstream changes (presumably #131573) made this pull request unmergeable. Please resolve the merge conflicts.

@workingjubilee
library: Stabilize const_intrinsic_forget
9a52300 
This is an implicit requirement of stabilizing `const_ptr_write`.

Const-stabilizes the internal `core::intrinsics`:
- `forget`
@workingjubilee
library: Stabilize const_ptr_write
ddc367d 
Const-stabilizes:
- `write`
- `write_bytes`
- `write_unaligned`

In the following paths:
- `core::ptr`
- `core::ptr::NonNull`
- pointer `<*mut T>`

Const-stabilizes the internal `core::intrinsics`:
- `write_bytes`
- `write_via_move`
@workingjubilee
library: Stabilize const_replace
187c8b0 
Depends on stabilizing `const_ptr_write`.

Const-stabilizes:
- `core::mem::replace`
- `core::ptr::replace`
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r=me once FCP is officially over

@rfcbot rfcbot added finished-final-comment-period The final comment period is finished for this PR / Issue. and removed final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. labels Oct 12, 2024
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rfcbot commented Oct 12, 2024

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.

@rfcbot rfcbot added the to-announce Announce this issue on triage meeting label Oct 12, 2024
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@bors r=RalfJung

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bors commented Oct 12, 2024

📌 Commit 187c8b0 has been approved by RalfJung

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 12, 2024
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bors added a commit to rust-lang-ci/rust that referenced this pull request Oct 12, 2024
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Auto merge of rust-lang#131612 - tgross35:rollup-zy3yg4p, r=tgross35
6b9676b 
Rollup of 7 pull requests

Successful merges:

 - rust-lang#130870 (Add suggestion for removing invalid path sep `::` in fn def)
 - rust-lang#130954 (Stabilize const `ptr::write*` and `mem::replace`)
 - rust-lang#131233 (std: fix stdout-before-main)
 - rust-lang#131590 (yeet some clones)
 - rust-lang#131596 (mark InterpResult as must_use)
 - rust-lang#131597 (Take a display name for `tool_check_step!`)
 - rust-lang#131605 (`LLVMConstInt` only allows integer types)

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 8a86f1d into rust-lang:master Oct 12, 2024
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@rustbot rustbot added this to the 1.83.0 milestone Oct 12, 2024
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Oct 12, 2024
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Unrolled build for rust-lang#130954
c8df3ff 
Rollup merge of rust-lang#130954 - workingjubilee:stabilize-const-mut-fn, r=RalfJung

Stabilize const `ptr::write*` and `mem::replace`

Since `const_mut_refs` and `const_refs_to_cell` have been stabilized, we may now also stabilize the ability to write to places during const evaluation inside our library API. So, we now propose the `const fn` version of `ptr::write` and its variants. This allows us to also stabilize `mem::replace` and `ptr::replace`.
- const `mem::replace`: rust-lang#83164 (comment)
- const `ptr::write{,_bytes,_unaligned}`: rust-lang#86302 (comment)

Their implementation requires an additional internal stabilization of `const_intrinsic_forget`, which is required for `*::write*` and thus `*::replace`. Thus we const-stabilize the internal intrinsics `forget`, `write_bytes`, and `write_via_move`.
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A-const-eval Area: Constant evaluation (MIR interpretation) A-const-fn Area: const fn foo(..) {..}. Pure functions which can be applied at compile time. A-testsuite Area: The testsuite used to check the correctness of rustc disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. F-const_mut_refs `#![feature(const_mut_refs)]` F-const_refs_to_cell `#[feature(const_refs_to_cell)]` finished-final-comment-period The final comment period is finished for this PR / Issue. I-lang-easy-decision Issue: The decision needed by the team is conjectured to be easy. S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. S-waiting-on-fcp Status: PR is in FCP and is awaiting for FCP to complete. T-lang Relevant to the language team, which will review and decide on the PR/issue. to-announce Announce this issue on triage meeting WG-const-eval Working group: Const evaluation
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Tracking Issue for const_ptr_write Tracking Issue for const_replace