Fix `LazyLock` poison panic message #145307

connortsui20 · 2025-08-12T12:27:09Z

Fixes the issue raised in #144872 (comment)

library/std/src/sync/lazy_lock.rs

library/std/tests/sync/lazy_lock.rs

bors · 2025-08-19T00:32:42Z

☔ The latest upstream changes (presumably #145489) made this pull request unmergeable. Please resolve the merge conflicts.

connortsui20 · 2025-08-19T02:41:32Z

@bjorn3 just a bump on my question in #145307 (comment), do you think it makes sense to add an argument to every implementation's call_once and wait functions for this? It's not a super difficult change, but I'm worried that it will make everything more complicated for what is probably not too much benefit.

Though I might be misunderstanding something: My understanding of the issue here is just that catch_unwind doesn't prevent the first message being printed. Is something else happening as well that is not obvious? I don't fully understand the foreign exception thing either and why that is important.

bjorn3 · 2025-08-19T08:34:32Z

I don't fully understand the foreign exception thing either and why that is important.

A foreign exception would be for example a C++ exception that unwinds though Rust code. Foreign exceptions can't be safely catched and rethrown. For example for C++ this would require calling a C++ runtime function to link the exception from the list of exceptions and later relink it. We can't do this in Rust as we can't depend on any particular C++ runtime or even any C++ runtime existing at all. For this reason trying to catch a foreign exception currently aborts the entire process.

rustbot · 2025-08-21T21:13:40Z

This PR was rebased onto a different master 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.

library/std/src/sys/sync/once/mod.rs

library/std/src/sync/lazy_lock.rs

Fixes an issue where if the underlying `Once` panics because it is poisoned, the panic displays the wrong message. Signed-off-by: Connor Tsui <[email protected]>

connortsui20 · 2025-08-22T19:05:35Z

library/std/tests/sync/lazy_lock.rs

-#[test]
-#[should_panic = "has previously been poisoned"]
-fn lazy_force_mut_panic() {
-    let mut lazy = LazyLock::<String>::new(|| panic!());
-    panic::catch_unwind(panic::AssertUnwindSafe(|| {
-        let _ = LazyLock::force_mut(&mut lazy);
-    }))
-    .unwrap_err();
-    let _ = &*lazy;
-}


This is moved down and renamed to lazy_deref_mut_panic

Amanieu · 2025-08-22T20:54:54Z

@bors r+

bors · 2025-08-22T20:54:57Z

📌 Commit 06eb782 has been approved by Amanieu

It is now in the queue for this repository.

…r=Amanieu Fix `LazyLock` poison panic message Fixes the issue raised in rust-lang#144872 (comment) r? `@Amanieu`

Rollup of 7 pull requests Successful merges: - #144452 (std/sys/fd: Relax `READ_LIMIT` on Darwin) - #145307 (Fix `LazyLock` poison panic message) - #145515 (Optimize `char::encode_utf8`) - #145540 (interpret/allocation: get_range on ProvenanceMap) - #145774 (Remove default opts from config) - #145780 (Do not warn about missing change ID in tarball builds) - #145781 (Remove profile section from Clippy) r? `@ghost` `@rustbot` modify labels: rollup

…r=Amanieu Fix `LazyLock` poison panic message Fixes the issue raised in rust-lang#144872 (comment) r? ``@Amanieu``

…r=Amanieu Fix `LazyLock` poison panic message Fixes the issue raised in rust-lang#144872 (comment) r? `@Amanieu`

…r=Amanieu Fix `LazyLock` poison panic message Fixes the issue raised in rust-lang#144872 (comment) r? ``@Amanieu``

Rollup of 6 pull requests Successful merges: - #144531 (Add lint against integer to pointer transmutes) - #144885 (Implement some more checks in `ptr_guaranteed_cmp`. ) - #145307 (Fix `LazyLock` poison panic message) - #145554 (rustc-dev-guide subtree update) - #145798 (Use unnamed lifetime spans as primary spans for `MISMATCHED_LIFETIME_SYNTAXES`) - #145799 (std/src/lib.rs: mention "search button" instead of "search bar") r? `@ghost` `@rustbot` modify labels: rollup

Rollup of 5 pull requests Successful merges: - #144531 (Add lint against integer to pointer transmutes) - #145307 (Fix `LazyLock` poison panic message) - #145554 (rustc-dev-guide subtree update) - #145798 (Use unnamed lifetime spans as primary spans for `MISMATCHED_LIFETIME_SYNTAXES`) - #145799 (std/src/lib.rs: mention "search button" instead of "search bar") r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #145307 - connortsui20:lazylock-poison-msg, r=Amanieu Fix `LazyLock` poison panic message Fixes the issue raised in #144872 (comment) r? ```@Amanieu```

jhpratt · 2025-08-24T07:09:16Z

still in queue

@bors r-

bors · 2025-08-24T07:09:58Z

⌛ Testing commit 06eb782 with merge 4eedad3...

jhpratt · 2025-08-24T07:11:03Z

@bors r- retry

Rollup of 5 pull requests Successful merges: - rust-lang/rust#144531 (Add lint against integer to pointer transmutes) - rust-lang/rust#145307 (Fix `LazyLock` poison panic message) - rust-lang/rust#145554 (rustc-dev-guide subtree update) - rust-lang/rust#145798 (Use unnamed lifetime spans as primary spans for `MISMATCHED_LIFETIME_SYNTAXES`) - rust-lang/rust#145799 (std/src/lib.rs: mention "search button" instead of "search bar") r? `@ghost` `@rustbot` modify labels: rollup

rustbot assigned Amanieu Aug 12, 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 Aug 12, 2025

connortsui20 force-pushed the lazylock-poison-msg branch 2 times, most recently from 2aea6c2 to e77c6fc Compare August 12, 2025 12:40

bjorn3 reviewed Aug 12, 2025

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connortsui20 force-pushed the lazylock-poison-msg branch from e77c6fc to 3ead751 Compare August 19, 2025 02:34

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connortsui20 force-pushed the lazylock-poison-msg branch from 3ead751 to 8e848c0 Compare August 21, 2025 21:13

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connortsui20 force-pushed the lazylock-poison-msg branch from 8e848c0 to d1f2324 Compare August 22, 2025 16:53

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Amanieu reviewed Aug 22, 2025

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modify LazyLock poison panic message

06eb782

Fixes an issue where if the underlying `Once` panics because it is poisoned, the panic displays the wrong message. Signed-off-by: Connor Tsui <[email protected]>

connortsui20 force-pushed the lazylock-poison-msg branch from d1f2324 to 06eb782 Compare August 22, 2025 19:00

connortsui20 commented Aug 22, 2025

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connortsui20 requested review from Amanieu and bjorn3 August 22, 2025 20:22

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 Aug 22, 2025

samueltardieu mentioned this pull request Aug 23, 2025

Rollup of 7 pull requests #145785

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jhpratt added a commit to jhpratt/rust that referenced this pull request Aug 23, 2025

Rollup merge of rust-lang#145307 - connortsui20:lazylock-poison-msg, …

0ece83f

…r=Amanieu Fix `LazyLock` poison panic message Fixes the issue raised in rust-lang#144872 (comment) r? ``@Amanieu``

jhpratt mentioned this pull request Aug 23, 2025

Rollup of 6 pull requests #145802

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Zalathar added a commit to Zalathar/rust that referenced this pull request Aug 24, 2025

Rollup merge of rust-lang#145307 - connortsui20:lazylock-poison-msg, …

fa990f4

…r=Amanieu Fix `LazyLock` poison panic message Fixes the issue raised in rust-lang#144872 (comment) r? `@Amanieu`

Zalathar mentioned this pull request Aug 24, 2025

Rollup of 14 pull requests #145803

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Zalathar added a commit to Zalathar/rust that referenced this pull request Aug 24, 2025

Rollup merge of rust-lang#145307 - connortsui20:lazylock-poison-msg, …

9636f98

…r=Amanieu Fix `LazyLock` poison panic message Fixes the issue raised in rust-lang#144872 (comment) r? ``@Amanieu``

Zalathar mentioned this pull request Aug 24, 2025

Rollup of 6 pull requests #145804

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jhpratt mentioned this pull request Aug 24, 2025

Rollup of 5 pull requests #145805

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bors merged commit d5340c2 into rust-lang:master Aug 24, 2025
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rustbot added this to the 1.91.0 milestone Aug 24, 2025

rust-timer added a commit that referenced this pull request Aug 24, 2025

Unrolled build for #145307

762d21b

Rollup merge of #145307 - connortsui20:lazylock-poison-msg, r=Amanieu Fix `LazyLock` poison panic message Fixes the issue raised in #144872 (comment) r? ```@Amanieu```

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Fix `LazyLock` poison panic message #145307

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