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"spawned process is not wait()ed on in all code paths" when ? used in chain call before spawn() #14911

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lyskov opened this issue May 28, 2025 · 2 comments · Fixed by #14912
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"spawned process is not wait()ed on in all code paths" when ? used in chain call before spawn() #14911

lyskov opened this issue May 28, 2025 · 2 comments · Fixed by #14912
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@samueltardieu
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C-bug Category: Clippy is not doing the correct thing I-false-positive Issue: The lint was triggered on code it shouldn't have

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@lyskov
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lyskov commented May 28, 2025 •
edited by rustbot
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Summary

Clippy flag command.spawn() code when ? used in daisy-chain calls before the spawn got called and .expect used on spawn invocation.

Interestingly, changing expect to ? on spawn() clear the the error:

fn test_1_passed() -> std::io::Result<String> {
    let (mut recv, send) = std::io::pipe()?;
    let mut command = Command::new("ls").stdout(send.try_clone()?).spawn()?;
    command.wait()?;
    Ok("".into())
}

Lint Name

clippy::zombie_processes

Reproducer

I tried this code:

fn test_1_flagged() -> std::io::Result<String> {
    let (mut recv, send) = std::io::pipe()?;
    let mut command = Command::new("ls")
    .stdout(send.try_clone()?)
    .spawn().expect("Could not spawn new process...");
    command.wait()?;
    Ok("".into())
}

I expected to see this happen: no issue

Instead, this happened: "spawned process is not wait()ed on in all code paths" highlighting send.try_clone()? as offending part.

Version

rustc 1.87.0 (17067e9ac 2025-05-09)
binary: rustc
commit-hash: 17067e9ac6d7ecb70e50f92c1944e545188d2359
commit-date: 2025-05-09
host: aarch64-apple-darwin
release: 1.87.0
LLVM version: 20.1.1
@lyskov lyskov added C-bug Category: Clippy is not doing the correct thing I-false-negative Issue: The lint should have been triggered on code, but wasn't labels May 28, 2025
@samueltardieu
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@rustbot label -I-false-negative +I-false-positive
@rustbot claim

@rustbot rustbot added I-false-positive Issue: The lint was triggered on code it shouldn't have and removed I-false-negative Issue: The lint should have been triggered on code, but wasn't labels May 28, 2025
@samueltardieu samueltardieu mentioned this issue May 28, 2025
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@lyskov
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lyskov commented May 28, 2025

Thank you for looking this up @samueltardieu !

github-merge-queue bot pushed a commit that referenced this issue Jun 3, 2025
@Jarcho
zombie_processes: do not complain about early early returns (#14912)
716eadf 
If an early return is found under the HIR local declaration node but
before the child process is created, it should not trigger the lint
because the child process has not yet been created.

changelog: [`zombie_process`]: do not complain about early early returns

Fixes #14911
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@samueltardieu samueltardieu

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C-bug Category: Clippy is not doing the correct thing I-false-positive Issue: The lint was triggered on code it shouldn't have
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zombie_processes: do not complain about early early returns samueltardieu/rust-clippy
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@samueltardieu @lyskov @rustbot