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path/filepath: Clean changed in Go 1.20 #58348

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bep opened this issue Feb 6, 2023 · 6 comments
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path/filepath: Clean changed in Go 1.20 #58348

bep opened this issue Feb 6, 2023 · 6 comments
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Documentation FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
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Go1.21

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@bep
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bep commented Feb 6, 2023

I have some GitHub action tests that started to fail on Windows after I bumped the build matrix to Go 1.20.

I have distilled the issue into this small repo: https://github.com/bep/go120winpathregression

--- FAIL: TestTo (0.00s)
    lib_test.go:12: 
        error:
          values are not equal
        got:
          "\\\\\\\\post"
        want:
          "\\post"
        stack:
          D:/a/go[12](https://github.com/bep/go120winpathregression/actions/runs/4102512994/jobs/7075566395#step:11:13)0winpathregression/go120winpathregression/lib_test.go:12
            c.Assert(Clean("////post/////"), qt.Equals, filepath.FromSlash("/post"))

I have looked closely in the release notes for Go 1.20 about this, but that does not mention this change. Also, the GoDoc for filepath.Clean is pretty clear about what happens to "multiple Separator elements":

  1. Replace multiple Separator elements with a single one.
@bep bep mentioned this issue Feb 6, 2023
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@seankhliao
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cc @neild regression from #56336 ?

@seankhliao seankhliao changed the title filepath: Clean changed in Go 1.20 path/filepath: Clean changed in Go 1.20 Feb 6, 2023
@seankhliao seankhliao added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Feb 6, 2023
@bep
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bep commented Feb 6, 2023

Looking back at the original failing test, I don't see why that should not use path.Clean, so I'm going to fix that, but I still think the above test case looks like a regression (esp. considering the documentation).

@neild
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neild commented Feb 6, 2023

filepath.Clean doesn't clean the volume name component of Windows paths. This is longstanding behavior:

filepath.Clean(`\\a\b\\c`) = `\\a\b\c`

I see that this isn't documented, however. It should be.

As of Go 1.20, we do a better job of identifying volume names, and we're more lax about accepting invalid volume names. \\\\post is not a valid Windows path, because it contains empty host and share components (the first two path components after a leading \\). Previously, filepath considered this to have a zero-length volume name component; it now considers it to have the (invalid) volume name \\\\.

I don't think this is a regression, since filepath.Clean has always (or at least long) preserved a \\ prefix in valid Windows filenames.

But we should fix the docs.

@bcmills bcmills added Documentation NeedsFix The path to resolution is known, but the work has not been done. labels Feb 6, 2023
@bcmills bcmills added this to the Go1.21 milestone Feb 6, 2023
@gopherbot gopherbot removed the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Feb 6, 2023
@bhavyastar
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Hey @bep @bcmills , Can I work on this issue?

@ianlancetaylor
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@bhavyastar Better documentation is always welcome. Thanks.

@antichris antichris mentioned this issue Feb 21, 2023
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@gopherbot
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Change https://go.dev/cl/469955 mentions this issue: path/filepath: document that Clean does not change Windows volume names

johanbrandhorst pushed a commit to Pryz/go that referenced this issue Feb 22, 2023
@neild @johanbrandhorst
path/filepath: document that Clean does not change Windows volume names
14174b7 
Fixes golang#58348

Change-Id: I4aac0285f11618a45aca6b13c2da2a10a803a9b5
Reviewed-on: https://go-review.googlesource.com/c/go/+/469955
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Damien Neil <dneil@google.com>
@imiric imiric mentioned this issue Feb 22, 2023
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