In `Option::get_or_insert_with()`, forget the `None` instead of dropping it. by kpreid · Pull Request #148562 · rust-lang/rust

kpreid · 2025-11-06T04:03:55Z

In Option::get_or_insert_with(), after replacing the None with Some, forget the None instead of dropping it.

This allows eliminating the T: [const] Destruct bounds, making the functions more flexible in (unstable) const contexts, and avoids generating an implicit drop_in_place::<Option<T>>() that will never do anything (and which might even persist after optimization).

rustbot · 2025-11-06T04:03:59Z

r? @ibraheemdev

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kpreid · 2025-11-06T04:06:17Z

cc @cyb0124 (this change is based on their idea)

library/coretests/tests/option.rs

library/core/src/option.rs

hkBst

Thanks! Looks good to me.

View changes since this review

library/core/src/option.rs

…ing it. This allows eliminating the `T: [const] Destruct` bounds and avoids generating an implicit `drop_in_place::<Option<T>>()` that will never do anything. Ideally, the compiler would prove that that drop is not necessary itself, but it currently doesn't, even with `const_precise_live_drops` enabled.

ibraheemdev · 2026-02-09T22:50:12Z

The implementation looks good to me. r? libs-api for the unstable API change.

kpreid · 2026-03-09T18:15:18Z

Per advice:

@rustbot label -S-waiting-on-review +S-waiting-on-t-libs-api

rustbot · 2026-03-09T18:15:21Z

Error: Unknown labels: S-waiting-on-libs-api

Please file an issue on GitHub at triagebot if there's a problem with this bot, or reach out on #triagebot on Zulip.

oli-obk · 2026-03-09T19:01:16Z

Can you check the final optimized runtime MIR before and after your change? I'm not sure we're optimizing the new code properly.

Also wondering about this pattern in general. Seems like sth const precise live drops could also handle, haven't looked at that in forever so I don't remember the details of it.

Anyway, if the final runtime MIR looks good, let's merge this

kpreid · 2026-03-09T19:37:35Z

Can you check the final optimized runtime MIR before and after your change? I'm not sure we're optimizing the new code properly.

I’m not familiar with how to do that, but I will look into it.

Seems like sth const precise live drops could also handle,

See prior discussion #148562 (comment) — in brief, having const_precise_live_drops would mean we are having the compiler doing static checking on how control flow affects values (whether the option is None), which is something that we generally only do for lint (e.g. if false {} is not counted as unreachable code).

kpreid · 2026-03-09T21:15:31Z

oli-obk and I have looked at the MIR through dropping both implementations into Compiler Explorer and it seems generally similar, but also not very optimized either before or after.

@rustbot label +const-hack

rustbot · 2026-03-09T21:15:34Z

Error: Unknown labels: const-hack

Please file an issue on GitHub at triagebot if there's a problem with this bot, or reach out on #triagebot on Zulip.

oli-obk · 2026-03-09T21:39:44Z

@bors r+ rollup

r? @oli-obk

rust-bors · 2026-03-09T21:39:47Z

📋 This PR cannot be approved because it currently has the following label: S-waiting-on-t-libs-api.

In `Option::get_or_insert_with()`, forget the `None` instead of dropping it. Per #148486 (comment) In `Option::get_or_insert_with()`, after replacing the `None` with `Some`, forget the `None` instead of dropping it. This allows eliminating the `T: [const] Destruct` bounds, making the functions more flexible in (unstable) const contexts, and avoids generating an implicit `drop_in_place::<Option<T>>()` that will never do anything (and which might even persist after optimization).

In `Option::get_or_insert_with()`, forget the `None` instead of dropping it. Per rust-lang#148486 (comment) In `Option::get_or_insert_with()`, after replacing the `None` with `Some`, forget the `None` instead of dropping it. This allows eliminating the `T: [const] Destruct` bounds, making the functions more flexible in (unstable) const contexts, and avoids generating an implicit `drop_in_place::<Option<T>>()` that will never do anything (and which might even persist after optimization).

matthiaskrgr · 2026-03-09T21:52:05Z

@bors yield

rust-bors · 2026-03-09T21:52:08Z

Auto build was cancelled. Cancelled workflows:

https://github.com/rust-lang/rust/actions/runs/22876376170

The next pull request likely to be tested is #153628.

Rollup of 8 pull requests Successful merges: - #148562 (In `Option::get_or_insert_with()`, forget the `None` instead of dropping it.) - #149931 (rustdoc: don't give depreciation notes special handling) - #153608 (ast_passes: unsupported arch w/ scalable vectors) - #153609 (Add missing `Diag::with_span_suggestion_with_style` method) - #153610 (Only lint unused features if they are unstable) - #153616 (Update `sysinfo` version to `0.38.4`) - #153619 (Update books) - #153624 (Ping fmease on parser modifications)

In `Option::get_or_insert_with()`, forget the `None` instead of dropping it. Per #148486 (comment) In `Option::get_or_insert_with()`, after replacing the `None` with `Some`, forget the `None` instead of dropping it. This allows eliminating the `T: [const] Destruct` bounds, making the functions more flexible in (unstable) const contexts, and avoids generating an implicit `drop_in_place::<Option<T>>()` that will never do anything (and which might even persist after optimization).

Zalathar · 2026-03-10T03:12:13Z

The dist-x86_64-linux job is stuck.

@bors yield

rust-bors · 2026-03-10T03:12:15Z

Auto build was cancelled. Cancelled workflows:

https://github.com/rust-lang/rust/actions/runs/22877728575

The next pull request likely to be tested is #153631.

Rollup of 4 pull requests Successful merges: - #148562 (In `Option::get_or_insert_with()`, forget the `None` instead of dropping it.) - #153325 (tests/ui/cfg: add annotations for reference rules) - #153621 (Remove `TyCtxt::node_span_lint` method) - #153627 (rustdoc-json: Improve docs for `ItemEnum::item_kind`)

In `Option::get_or_insert_with()`, forget the `None` instead of dropping it. Per #148486 (comment) In `Option::get_or_insert_with()`, after replacing the `None` with `Some`, forget the `None` instead of dropping it. This allows eliminating the `T: [const] Destruct` bounds, making the functions more flexible in (unstable) const contexts, and avoids generating an implicit `drop_in_place::<Option<T>>()` that will never do anything (and which might even persist after optimization).

rust-bors · 2026-03-10T09:35:26Z

💔 Test for 8744ff0 failed: CI. Failed job:

auto - x86_64-gnu-gcc (web logs, enhanced plaintext logs)

Zalathar · 2026-03-10T09:50:00Z

@bors retry (network failure)

Rollup of 4 pull requests Successful merges: - #148562 (In `Option::get_or_insert_with()`, forget the `None` instead of dropping it.) - #153325 (tests/ui/cfg: add annotations for reference rules) - #153621 (Remove `TyCtxt::node_span_lint` method) - #153627 (rustdoc-json: Improve docs for `ItemEnum::item_kind`)

rust-log-analyzer · 2026-03-10T10:05:42Z

A job failed! Check out the build log: (web) (plain enhanced) (plain)

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/dev/sda15      105M  6.2M   99M   6% /boot/efi
tmpfs           1.6G   12K  1.6G   1% /run/user/1001
================================================================================

Sufficient disk space available (95001912KB >= 52428800KB). Skipping cleanup.
##[group]Run src/ci/scripts/setup-environment.sh
src/ci/scripts/setup-environment.sh
shell: /usr/bin/bash --noprofile --norc -e -o pipefail {0}

Rollup of 4 pull requests Successful merges: - #148562 (In `Option::get_or_insert_with()`, forget the `None` instead of dropping it.) - #153325 (tests/ui/cfg: add annotations for reference rules) - #153621 (Remove `TyCtxt::node_span_lint` method) - #153627 (rustdoc-json: Improve docs for `ItemEnum::item_kind`)

Rollup merge of #148562 - kpreid:get-init-drop, r=oli-obk In `Option::get_or_insert_with()`, forget the `None` instead of dropping it. Per #148486 (comment) In `Option::get_or_insert_with()`, after replacing the `None` with `Some`, forget the `None` instead of dropping it. This allows eliminating the `T: [const] Destruct` bounds, making the functions more flexible in (unstable) const contexts, and avoids generating an implicit `drop_in_place::<Option<T>>()` that will never do anything (and which might even persist after optimization).

rustbot assigned ibraheemdev Nov 6, 2025

rustbot 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 Nov 6, 2025

hkBst suggested changes Nov 6, 2025

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kpreid force-pushed the get-init-drop branch 2 times, most recently from ecc05f4 to 2e71187 Compare November 6, 2025 23:31

hkBst approved these changes Nov 7, 2025

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clarfonthey reviewed Nov 23, 2025

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kpreid force-pushed the get-init-drop branch from 2e71187 to cbc408f Compare November 23, 2025 22:46

kpreid force-pushed the get-init-drop branch from cbc408f to c1b51dd Compare November 23, 2025 23:00

rustbot added the T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. label Feb 9, 2026

rustbot assigned the8472 and unassigned ibraheemdev Feb 9, 2026

rustbot added S-waiting-on-t-libs-api Status: Awaiting decision from T-libs-api and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 9, 2026

rustbot assigned oli-obk and unassigned the8472 Mar 9, 2026

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rust-bors bot added the S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. label Mar 9, 2026

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matthiaskrgr mentioned this pull request Mar 9, 2026

Rollup of 8 pull requests #153628

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matthiaskrgr mentioned this pull request Mar 10, 2026

Rollup of 4 pull requests #153642

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rust-bors bot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Mar 10, 2026

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rustdoc-json: Improve docs for ItemEnum::item_kind #153627

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rust-bors bot merged commit ce97229 into rust-lang:main Mar 10, 2026
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rustbot added this to the 1.96.0 milestone Mar 10, 2026

kpreid deleted the get-init-drop branch March 10, 2026 20:40

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