Skip to content

1.95 beta regression: "temporary value dropped while borrowed" #153850

Closed
#154074
Closed
1.95 beta regression: "temporary value dropped while borrowed"#153850
#154074
Labels
A-destructorsArea: Destructors (`Drop`, …)A-fmtArea: `core::fmt`A-macrosArea: All kinds of macros (custom derive, macro_rules!, proc macros, ..)A-temporary-lifetime-extensionArea: temporary lifetime extensionC-bugCategory: This is a bug.P-highHigh priorityS-has-bisectionStatus: A bisection has been found for this issueS-has-mcveStatus: A Minimal Complete and Verifiable Example has been found for this issueT-libsRelevant to the library team, which will review and decide on the PR/issue.regression-from-stable-to-betaPerformance or correctness regression from stable to beta.
Milestone
1.95.0

Description

@theemathas
theemathas
opened on Mar 14, 2026

Regression found by the 1.95 beta crater run.

[INFO] [stdout] error[E0716]: temporary value dropped while borrowed
[INFO] [stdout]    --> src/lib.rs:229:34
[INFO] [stdout]     |
[INFO] [stdout] 227 | // ...                   dbg!(
[INFO] [stdout] 228 | || ...                       x.value().score / x.value().playouts as f32,
[INFO] [stdout] 229 | || ...                       &x.id(),
[INFO] [stdout]     | ||                            ^^^^^^ creates a temporary value which is freed while still in use
[INFO] [stdout] 230 | || ...                       x.value().playouts,
[INFO] [stdout] 231 | || ...                   )
[INFO] [stdout]     | ||_______________________- temporary value is freed at the end of this statement
[INFO] [stdout] 232 | |  ...                   .0,
[INFO] [stdout]     | |_________________________- borrow later used here
[INFO] [stdout]     |
[INFO] [stdout]     = note: consider using a `let` binding to create a longer lived value
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stderr] error: could not compile `monte_carlo` (lib) due to 1 previous error; 2 warnings emitted
[INFO] [stdout] For more information about this error, try `rustc --explain E0716`.

https://crater-reports.s3.amazonaws.com/beta-1.95-3/1.95.0-beta.3/reg/monte_carlo-0.1.1/log.txt

Activity

  1. theemathas
    added
    regression-from-stable-to-betaPerformance or correctness regression from stable to beta.
    C-bugCategory: This is a bug.
    E-needs-bisectionCall for participation: This issue needs bisection: https://github.com/rust-lang/cargo-bisect-rustc
    E-needs-mcveCall for participation: This issue has a repro, but needs a Minimal Complete and Verifiable Example
    on Mar 14, 2026
  2. rustbot
    added
    I-prioritizeIssue needs a team member to assess the impact. Will be replaced by P-{low,medium,high,critical}
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    on Mar 14, 2026
  3. theemathas
    added a parent issue on Mar 14, 2026
  4. jieyouxu
    added
    T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.
    on Mar 14, 2026

  5. theemathas commented on Mar 14, 2026

    @theemathas
    theemathas
    on Mar 14, 2026
    ContributorAuthor

    Minimal reproducer:

    fn one() -> i32 { 1 }

fn main() {
    dbg!(0, &one()).0;
}
    Error output on beta 
    error[E0716]: temporary value dropped while borrowed
 --> src/main.rs:4:14
  |
4 |     dbg!(0, &one()).0;
  |     ---------^^^^^---
  |     |        |
  |     |        creates a temporary value which is freed while still in use
  |     temporary value is freed at the end of this statement
  |     borrow later used here
  |
help: consider using a `let` binding to create a longer lived value
  |
4 ~     let binding = one();
5 ~     dbg!(0, &binding).0;
  |

For more information about this error, try `rustc --explain E0716`.
  6. theemathas
    added
    S-has-mcveStatus: A Minimal Complete and Verifiable Example has been found for this issue
    and removed
    E-needs-mcveCall for participation: This issue has a repro, but needs a Minimal Complete and Verifiable Example
    on Mar 14, 2026

  7. theemathas commented on Mar 14, 2026

    @theemathas
    theemathas
    on Mar 14, 2026
    ContributorAuthor

    Bisection result:

    ********************************************************************************
Regression in 4d38622e8bec00a9001264c4e9f4723fceca23cb
********************************************************************************

Attempting to search unrolled perf builds
Found commits ["a35802ec", "5d0accfe", "339ebba7", "cf4dd004", "51885a1e", "008d732c", "39ee306a", "299c6ea3", "87aa422a", "280da588"]
installing a35802ecf86de711020db33066f7968a9b1fd2c5
uninstalling a35802ecf86de711020db33066f7968a9b1fd2c5
installing 5d0accfebb901c0dc047ae0601dd31537af58908
uninstalling 5d0accfebb901c0dc047ae0601dd31537af58908
installing 339ebba77c0b673e31199d9792986008df623218
uninstalling 339ebba77c0b673e31199d9792986008df623218
installing cf4dd004bd807b783e6aeb2280dd40377935e04c
uninstalling cf4dd004bd807b783e6aeb2280dd40377935e04c
installing 51885a1eb22206f02abc1d457f338d943ccfc31d
uninstalling 51885a1eb22206f02abc1d457f338d943ccfc31d
installing 008d732cc606bd816317791b6bb258e2a7351471
uninstalling 008d732cc606bd816317791b6bb258e2a7351471
installing 39ee306a949b0f8eb7233e874f5cade6a399ed3c
uninstalling 39ee306a949b0f8eb7233e874f5cade6a399ed3c
installing 299c6ea372b0a1716cc5faab39c5530183cb2b15
uninstalling 299c6ea372b0a1716cc5faab39c5530183cb2b15
installing 87aa422a4eefb11c97a8cb99a49bdf0375e833a3
uninstalling 87aa422a4eefb11c97a8cb99a49bdf0375e833a3
installing 280da5887cb785378f7377d39726abc804049c9d
uninstalling 280da5887cb785378f7377d39726abc804049c9d
ERROR: none of the toolchains satisfied the predicate

    Presumably regressed in #149869. cc @joboet @Mark-Simulacrum

  8. theemathas
    added
    S-has-bisectionStatus: A bisection has been found for this issue
    and removed
    E-needs-bisectionCall for participation: This issue needs bisection: https://github.com/rust-lang/cargo-bisect-rustc
    T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.
    on Mar 14, 2026

  9. 21 remaining items

  10. github-actions
    added a commit that references this issue on Mar 30, 2026

    Rollup merge of #154074 - dianne:dbg-temp-scopes, r=Mark-Simulacrum

    f806c33
  11. flip1995
    added a commit that references this issue on Apr 2, 2026

    Rollup merge of #154074 - dianne:dbg-temp-scopes, r=Mark-Simulacrum

    4efda7a

  12. cuviper commented on Apr 4, 2026

    @cuviper
    cuviper
    on Apr 4, 2026
    Member

    Should be all set with #154725, 1.95.0-beta.7. The minimal reproducer passes with this beta on the playground.

  13. cuviper
    closed this as completedon Apr 4, 2026
  14. rust-bors
    added 2 commits that reference this issue on Apr 9, 2026

    Auto merge of #154999 - cuviper:beta-next, r=cuviper

    2eccf47

    Auto merge of #154999 - cuviper:beta-next, r=cuviper

    2c8c85d
  15. rust-bors
    added a commit that references this issue on May 19, 2026

    Auto merge of #156589 - cuviper:revert-dbg-tearing, r=the8472

    4b97926
  16. pull
    added a commit that references this issue on May 20, 2026

    Auto merge of #156589 - cuviper:revert-dbg-tearing, r=the8472

    eabe660
  17. flip1995
    added a commit that references this issue on May 28, 2026

    Auto merge of #156589 - cuviper:revert-dbg-tearing, r=the8472

    942dc28
  18. github-actions
    added a commit that references this issue on May 30, 2026

    Auto merge of #156589 - cuviper:revert-dbg-tearing, r=the8472

    0fb8669
  19. pull
    added a commit that references this issue on Jun 7, 2026

    Auto merge of #156589 - cuviper:revert-dbg-tearing, r=the8472

    9d5273a
  20. github-actions
    added a commit that references this issue on Jun 8, 2026

    Auto merge of #156589 - cuviper:revert-dbg-tearing, r=the8472

    96403ef
  21. ghaaj
    added a commit that references this issue on Aug 7, 2026

    Auto merge of #156589 - cuviper:revert-dbg-tearing, r=the8472

    cdd93bb
  22. flip1995
    added 2 commits that reference this issue on Aug 17, 2026

    Rollup merge of #154074 - dianne:dbg-temp-scopes, r=Mark-Simulacrum

    8f3c650

    Auto merge of #156589 - cuviper:revert-dbg-tearing, r=the8472

    1f738b8
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Metadata

Metadata

Assignees

No one assigned

    Labels

    A-destructorsArea: Destructors (`Drop`, …)A-fmtArea: `core::fmt`A-macrosArea: All kinds of macros (custom derive, macro_rules!, proc macros, ..)A-temporary-lifetime-extensionArea: temporary lifetime extensionC-bugCategory: This is a bug.P-highHigh priorityS-has-bisectionStatus: A bisection has been found for this issueS-has-mcveStatus: A Minimal Complete and Verifiable Example has been found for this issueT-libsRelevant to the library team, which will review and decide on the PR/issue.regression-from-stable-to-betaPerformance or correctness regression from stable to beta.

    Type

    No type

    Projects

    No projects

      Milestone

      Relationships

      None yet

      Development

      No branches or pull requests

      Issue actions