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Windows: Allow running processes whose path exceeds the legacy MAX_PATH #86406

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ChrisDenton
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On Windows Command currently fails when run using paths longer than the legacy MAX_PATH. This PR allows running such executables while leaving the behaviour of shorter paths unchanged.

This does not risk changing the behaviour of currently working code. It only allows something to work that would previously fail.

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r? @Mark-Simulacrum

(rust-highfive has picked a reviewer for you, use r? to override)

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 17, 2021
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ChrisDenton commented Jun 22, 2021 •
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It was pointed out to me that my previous implementation meant paths would have slightly different behaviours, depending only on the length, because of the way .exe is, or isn't, appended after being passed to CreateProcessW. For the sake of consistency I've unified long and short path handling.

Note that CreateProcessW has slightly weird rules here and Rust could certainly use a simpler strategy. However I'd rather not do that as a side effect of this change. So I've opted to maintain the existing behaviour for now.

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r? @joshtriplett perhaps? I'm not sure if we have anyone with close enough familiarity or knowledge of Windows primitives to review this, but I don't think I'm the right person.

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jyn514 commented Jul 8, 2021

Cc @retep998

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bors commented Jul 9, 2021

☔ The latest upstream changes (presumably #85832) made this pull request unmergeable. Please resolve the merge conflicts.

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Parse a Windows file name without normalization
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@ChrisDenton
Windows: Allow running processes whose path exceeds the legacy MAX_PATH
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Previously `Command` would simply fail when run using long paths.

This also implements the `CreateProcessW` rules for appending `.exe`. This is to ensure both backwards compatibility and consistent behaviour between both long and short paths. However, this could be changed (and hopefully simplified) in the future.
@JohnCSimon JohnCSimon added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 25, 2021
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I now minded to close this PR in favour of doing a bigger overhaul of how Command looks for executables on Windows. On the internals forum there seems (so far) to be consensus that it should only look in PATH. Doing that manually would make this unnecessary.

@ChrisDenton ChrisDenton closed this Aug 2, 2021
@ehuss ehuss mentioned this pull request Aug 6, 2021
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@ChrisDenton ChrisDenton deleted the long-path-command branch October 7, 2022 00:57
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