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constify TryFrom<Vec> for array#155616

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Lars-Schumann:const-array-try-from-vec
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constify TryFrom<Vec> for array#155616
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rust-lang:mainfrom
Lars-Schumann:const-array-try-from-vec

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@Lars-Schumann Lars-Schumann commented Apr 21, 2026 •
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Related issues #79597, #143773, #133214

this makes Vec const Destruct along the way.

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. 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 Apr 21, 2026
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r? @jackh726

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@Lars-Schumann Lars-Schumann marked this pull request as draft April 21, 2026 21:26
@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 21, 2026
@Lars-Schumann Lars-Schumann force-pushed the const-array-try-from-vec branch from 9c141c1 to f59366f Compare April 21, 2026 21:29
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@Lars-Schumann Lars-Schumann force-pushed the const-array-try-from-vec branch from f59366f to 8acdb36 Compare April 22, 2026 07:26
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Lars-Schumann commented Apr 22, 2026
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Comment thread library/alloc/src/vec/mod.rs
@Lars-Schumann Lars-Schumann marked this pull request as ready for review April 22, 2026 08:01
@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Apr 22, 2026
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jackh726 commented Apr 23, 2026

r? libs-api

@rustbot rustbot added the T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. label Apr 23, 2026
@rustbot rustbot assigned the8472 and unassigned jackh726 Apr 23, 2026
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Lars-Schumann commented Apr 24, 2026

assigned reviewer seems inactive atm
r? rust-lang/wg-const-eval

@rustbot rustbot assigned lcnr and unassigned the8472 Apr 24, 2026
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lcnr commented May 5, 2026

r? oli

is this blocked on figuring out std constification

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lcnr commented May 5, 2026

r? oli-obk

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rustbot commented May 5, 2026

Failed to set assignee to oli: invalid assignee

Note: Only org members with at least the repository "read" role, users with write permissions, or people who have commented on the PR may be assigned.

@rustbot rustbot assigned oli-obk and unassigned lcnr May 5, 2026
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oli-obk commented May 6, 2026

Huh why does this affect mir-opts?

I think this is fine under std constification, because it tests a very specific use case of a core type like Vec. At minimum we should have const Drop for Vec

@oli-obk oli-obk removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label May 6, 2026
@oli-obk oli-obk added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label May 6, 2026
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Lars-Schumann commented May 6, 2026 •
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At minimum we should have const Drop for Vec

@oli-obk do you want me to limit the scope of this PR to that and remove the const TryFrom ?

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oli-obk commented May 6, 2026

I think it's trivial enough, and ppl were more worried about random std types than core types. So it should be fine, and feels like a core use case for const code to push things to a vec but still produce an array

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Lars-Schumann commented May 6, 2026

So then @rustbot ready ?

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels May 6, 2026
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oli-obk commented May 6, 2026

why does this affect mir-opts?

This still baffles me. Can't merge it without knowing why.

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Comment thread tests/mir-opt/pre-codegen/slice_iter.range_loop.PreCodegen.after.panic-abort.mir
Comment on lines +75 to +79
StorageLive(_7);
_7 = copy _4;
_4 = AddUnchecked(copy _7, const 1_usize);
_8 = Option::<usize>::Some(copy _7);
StorageDead(_7);
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@oli-obk oli-obk May 7, 2026 •
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I mean, this is probably an improvement, but what causes it? Do we have mir-opts that are checking constness of functions out of some reason?

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@Lars-Schumann Lars-Schumann force-pushed the const-array-try-from-vec branch from 8acdb36 to 74c398b Compare May 17, 2026 19:43
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rustbot commented May 17, 2026

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

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