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Fix: Drop ZST elements properly in array::map and array::try_map - #152248

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TusharB-07:fix-zst-drop-array-map
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Fix: Drop ZST elements properly in array::map and array::try_map#152248
TusharB-07 wants to merge 2 commits into
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TusharB-07:fix-zst-drop-array-map

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@TusharB-07TusharB-07 commented Feb 6, 2026•
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Fixes#152211

Previously, the Drain::drop implementation would skip dropping zero-sized types entirely, causing Drop implementations on ZSTs to never run when a closure panicked or exited early.

This fix adds a zst_processed counter to track how many ZST elements have been processed, ensuring that remaining unprocessed ZSTs are properly dropped when the Drain is dropped.

For ZSTs, conjure_zst() creates new values rather than moving from the array, so all N original elements remain and must be accounted for.

TusharB-07
Fix: Drop ZST elements properly in array::map and array::try_map
6b23f12
Fixesrust-lang#152211
Previously, the Drain::drop implementation would skip dropping
zero-sized types entirely, causing Drop implementations on ZSTs
to never run when a closure panicked or exited early.
This fix adds a zst_processed counter to track how many ZST elements
have been processed, ensuring that remaining unprocessed ZSTs are
properly dropped when the Drain is dropped.
For ZSTs, conjure_zst() creates new values rather than moving from
the array, so all N original elements remain and must be accounted for.
@rustbotrustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Feb 6, 2026
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r? @scottmcm

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@scottmcm

scottmcm commented Feb 6, 2026

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Ah, I see, this got screwed up in the const hackery.

It originally used a slice::IterMut to not have to think about ZSTs

https://github.com/rust-lang/rust/pull/107634/changes#diff-d391813c2568a5afd0555e6224d5168993b6ada448c4f1397799cb98b5b8a18bR32

Until the bots and CI are happy,
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@rustbotrustbot 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 Feb 6, 2026
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Reminder, once the PR becomes ready for a review, use @rustbot ready.

@lqd

lqd commented Feb 6, 2026

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There also already is another PR for this issue, in #152220

@scottmcmscottmcm assigned joboet and unassigned scottmcmFeb 6, 2026
@TusharB-07

TusharB-07 commented Feb 8, 2026

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@rustbot ready

@rustbotrustbot 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 Feb 8, 2026
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TusharB-07 commented Feb 9, 2026

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@rustbot claim

@rustbotrustbot assigned TusharB-07 and unassigned joboetFeb 9, 2026
@theemathas

theemathas commented Feb 10, 2026

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@workingjubilee This PR is now assigned to nobody. Is this intended?

@joboetjoboet self-assigned this Feb 10, 2026
@joboetjoboet mentioned this pull request Feb 11, 2026
Merged
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request Apr 27, 2026
@JonathanBrouwer
Rollup merge ofrust-lang#152487- joboet:array_map_zst, r=oli-obk
6779e67
core: drop unmapped ZSTs in array `map`
Fixesrust-lang#152211.
Alternative to rust-lang#152220 and rust-lang#152248.
This makes the `Drain` type use the same ZST-handling strategy as `slice::IterMut`, which stores the remaining length instead of a one-past-the-end pointer when the type is a ZST. I've also removed the const-generic `N` parameter from `Drain` to avoid unnecessary monomorphizations.
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request Apr 27, 2026
@JonathanBrouwer
Rollup merge ofrust-lang#152487- joboet:array_map_zst, r=oli-obk
76347ce
core: drop unmapped ZSTs in array `map`
Fixesrust-lang#152211.
Alternative to rust-lang#152220 and rust-lang#152248.
This makes the `Drain` type use the same ZST-handling strategy as `slice::IterMut`, which stores the remaining length instead of a one-past-the-end pointer when the type is a ZST. I've also removed the const-generic `N` parameter from `Drain` to avoid unnecessary monomorphizations.
rust-borsBot pushed a commit that referenced this pull request Apr 27, 2026
@bors
Auto merge of#152487- joboet:array_map_zst, r=oli-obk
44ae6c2
core: drop unmapped ZSTs in array `map`
Fixes#152211.
Alternative to #152220 and #152248.
This makes the `Drain` type use the same ZST-handling strategy as `slice::IterMut`, which stores the remaining length instead of a one-past-the-end pointer when the type is a ZST. I've also removed the const-generic `N` parameter from `Drain` to avoid unnecessary monomorphizations.
GuillaumeGomez added a commit to GuillaumeGomez/rust that referenced this pull request May 1, 2026
@GuillaumeGomez
Rollup merge ofrust-lang#152487- joboet:array_map_zst, r=oli-obk
c389685
core: drop unmapped ZSTs in array `map`
Fixesrust-lang#152211.
Alternative to rust-lang#152220 and rust-lang#152248.
This makes the `Drain` type use the same ZST-handling strategy as `slice::IterMut`, which stores the remaining length instead of a one-past-the-end pointer when the type is a ZST. I've also removed the const-generic `N` parameter from `Drain` to avoid unnecessary monomorphizations.
@joboet

joboet commented May 7, 2026

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I do prefer my own approach in #152487 so I'm going to close this PR. But thank you for your work regardless!

@joboetjoboet closed this May 7, 2026
@rustbotrustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label May 7, 2026
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request May 7, 2026
@JonathanBrouwer
Rollup merge ofrust-lang#152487- joboet:array_map_zst, r=oli-obk
ddf9bfb
core: drop unmapped ZSTs in array `map`
Fixesrust-lang#152211.
Alternative to rust-lang#152220 and rust-lang#152248.
This makes the `Drain` type use the same ZST-handling strategy as `slice::IterMut`, which stores the remaining length instead of a one-past-the-end pointer when the type is a ZST. I've also removed the const-generic `N` parameter from `Drain` to avoid unnecessary monomorphizations.
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request May 7, 2026
@JonathanBrouwer
Rollup merge ofrust-lang#152487- joboet:array_map_zst, r=oli-obk
92dbb8a
core: drop unmapped ZSTs in array `map`
Fixesrust-lang#152211.
Alternative to rust-lang#152220 and rust-lang#152248.
This makes the `Drain` type use the same ZST-handling strategy as `slice::IterMut`, which stores the remaining length instead of a one-past-the-end pointer when the type is a ZST. I've also removed the const-generic `N` parameter from `Drain` to avoid unnecessary monomorphizations.
rust-timer added a commit that referenced this pull request May 8, 2026
@rust-timer
Unrolled build for#152487
188cf0d
Rollup merge of #152487 - joboet:array_map_zst, r=oli-obk
core: drop unmapped ZSTs in array `map`
Fixes#152211.
Alternative to #152220 and #152248.
This makes the `Drain` type use the same ZST-handling strategy as `slice::IterMut`, which stores the remaining length instead of a one-past-the-end pointer when the type is a ZST. I've also removed the const-generic `N` parameter from `Drain` to avoid unnecessary monomorphizations.
bjorn3 pushed a commit to rust-lang/rustc_codegen_cranelift that referenced this pull request May 11, 2026
@JonathanBrouwer
Rollup merge of #152487 - joboet:array_map_zst, r=oli-obk
8231456
core: drop unmapped ZSTs in array `map`
Fixesrust-lang/rust#152211.
Alternative to rust-lang/rust#152220 and rust-lang/rust#152248.
This makes the `Drain` type use the same ZST-handling strategy as `slice::IterMut`, which stores the remaining length instead of a one-past-the-end pointer when the type is a ZST. I've also removed the const-generic `N` parameter from `Drain` to avoid unnecessary monomorphizations.
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array::map and array::try_map do not drop ZSTs properly

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