[6.2] Reset the working directory of child processes we spawn on Windows. #1219
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grynspan
commented
Jul 10, 2025
grynspan
commented
- Explanation: Works around a behavioural difference on Windows where a process prevents the deletion of its CWD which means exit tests can cause Foundation unit tests to fail.
- Scope: Windows exit tests.
- Issues: Exit tests crash main process on Windows (testing fails) #1209
- Original PRs: Reset the working directory of child processes we spawn on Windows. #1212
- Risk: Low, but it is a Windows-specific behavioural change so non-zero?
- Testing: Existing CI jobs and a new unit test.
- Reviewers: @stmontgomery @jmschonfeld @briancroom
…1212) This PR modifies the Windows implementation of `spawnProcess()` so that it sets the working directory of the new process to "C:\" (or thereabouts). This prevents a race condition on Windows because that system won't let you delete a directory if it's the working directory of any process. See [The Old New Thing](https://devblogs.microsoft.com/oldnewthing/20101109-00/?p=12323) for a very on-the-nose blog post. Note that we do not specify the value of the working directory in an exit test body. A test should generally not rely on it anyway because it is global state and any thread could change its value at any time. I haven't written a unit test for this change because it's unclear what I could write that would be easily verifiable, and because I don't know what state I might perturb outside such a test by calling `SetCurrentDirectory()`. Resolves #1209. (This is a speculative fix.) ### Checklist: - [x] Code and documentation should follow the style of the [Style Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md). - [x] If public symbols are renamed or modified, DocC references should be updated.
grynspan
requested review from
briancroom,
stmontgomery and
suzannaratcliff
as code owners
grynspan
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briancroom
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Jul 11, 2025
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