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Missing "unused variable" warning when using a match guard #151983

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#151990
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Missing "unused variable" warning when using a match guard#151983
#151990
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eggyal
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A-lintsArea: Lints (warnings about flaws in source code) such as unused_mut.C-bugCategory: This is a bug.L-unused_variablesLint: unused_variablesP-mediumMedium priorityT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.regression-from-stable-to-stablePerformance or correctness regression from one stable version to another.

Description

@nstoddard
nstoddard
opened on Feb 2, 2026

I tried this code:

fn main() {
    match Some(42) {
        Some(unused) if true => (),
        _ => (),
    }
}

I expected to see this happen: the compiler should warn that unused is unused.

Instead, this happened: the code compiles without any warnings, unless the if true part is removed.

Meta

rustc --version --verbose:

rustc 1.93.0 (254b59607 2026-01-19)
binary: rustc
commit-hash: 254b59607d4417e9dffbc307138ae5c86280fe4c
commit-date: 2026-01-19
host: x86_64-unknown-linux-gnu
release: 1.93.0
LLVM version: 21.1.8

Activity

  1. nstoddard
    added
    C-bugCategory: This is a bug.
    on Feb 2, 2026
  2. rustbot
    added
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    on Feb 2, 2026

  3. eggyal commented on Feb 2, 2026

    @eggyal
    eggyal
    on Feb 2, 2026
    Contributor

    @rustbot claim

  4. rustbot
    assigned
    eggyal
    on Feb 2, 2026

  5. theemathas commented on Feb 2, 2026

    @theemathas
    theemathas
    on Feb 2, 2026
    Contributor

    This emitted a warning in 1.91.0, but not 1.92.0.

  6. theemathas
    added
    A-lintsArea: Lints (warnings about flaws in source code) such as unused_mut.
    regression-from-stable-to-stablePerformance or correctness regression from one stable version to another.
    L-unused_variablesLint: unused_variables
    on Feb 2, 2026
  7. rustbot
    added
    I-prioritizeIssue needs a team member to assess the impact. Will be replaced by P-{low,medium,high,critical}
    on Feb 2, 2026
  8. theemathas
    added
    T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.
    and removed
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    on Feb 2, 2026

  9. mu001999 commented on Feb 2, 2026

    @mu001999
    mu001999
    on Feb 2, 2026
    Member

    Regression in ff6dc92, #142390

  10. apiraino commented on Feb 2, 2026

    @apiraino
    apiraino
    on Feb 2, 2026
    Contributor

    Assigning priority (discussion on Zulip).

    @rustbot label -I-prioritize +P-medium

  11. rustbot
    added
    P-mediumMedium priority
    and removed
    I-prioritizeIssue needs a team member to assess the impact. Will be replaced by P-{low,medium,high,critical}
    on Feb 2, 2026
  12. jhpratt
    added a commit that references this issue on Feb 3, 2026

    Rollup merge of rust-lang#151990 - eggyal:unused-in-match-with-guard,…

    b73b822
  13. rust-bors
    closed this as completedin b73b822on Feb 3, 2026
  14. rust-timer
    added a commit that references this issue on Feb 3, 2026

    Unrolled build for #151990

    6e45695
  15. github-actions
    added a commit that references this issue on Feb 5, 2026

    Rollup merge of #151990 - eggyal:unused-in-match-with-guard, r=nnethe…

    5834cb3
  16. flip1995
    added a commit that references this issue on Aug 17, 2026

    Rollup merge of #151990 - eggyal:unused-in-match-with-guard, r=nnethe…

    66b5e06
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A-lintsArea: Lints (warnings about flaws in source code) such as unused_mut.C-bugCategory: This is a bug.L-unused_variablesLint: unused_variablesP-mediumMedium priorityT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.regression-from-stable-to-stablePerformance or correctness regression from one stable version to another.

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