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fix: normalize stdin path to be relative to tree root #682

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fix: normalize stdin path to be relative to tree root #682

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36 changes: 36 additions & 0 deletions cmd/root_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2117,6 +2117,42 @@ func TestStdin(t *testing.T) {
}),
)

// verify that absolute paths work
absPath, err := filepath.Abs("test.nix")
as.NoError(err)
os.Stdin = test.TempFile(t, "", "stdin", &contents)

treefmt(t,
withArgs("--stdin", absPath),
withNoError(t),
withStats(t, map[stats.Type]int{
stats.Traversed: 1,
stats.Matched: 1,
stats.Formatted: 1,
stats.Changed: 1,
}),
withStdout(func(out []byte) {
as.Equal(`{ ...}: "hello"
`, string(out))
}),
)

// verify that absolute paths in subdirectories work with glob patterns
absPathInSubdir, err := filepath.Abs(filepath.Join("go", "main.go"))
as.NoError(err)
goContents := "package main\n"
os.Stdin = test.TempFile(t, "", "stdin", &goContents)

treefmt(t,
withArgs("--stdin", absPathInSubdir),
withNoError(t),
withStats(t, map[stats.Type]int{
stats.Traversed: 1,
stats.Matched: 1,
stats.Formatted: 1,
}),
)

// the nix formatters should have reduced the example to the following

// try a file that's outside of the project root
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20 changes: 17 additions & 3 deletions walk/walk.go
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Original file line number Diff line number Diff line change
Expand Up @@ -283,12 +283,26 @@ func NewCompositeReader(
}

path := paths[0]
resolvedPath, err := resolvePath(path)
if err != nil {
// If the path doesn't exist, we still want to make it relative to the root if possible.
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@jfly jfly Apr 5, 2026

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This smells weird to me. Could we just make do without trying to call resolvePath at all?

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@adrian-gierakowski adrian-gierakowski Apr 5, 2026

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I use resolvePath to match existing behaviour when used without --stdin. IMHO the behaviour should be the same between these 2 cases when main.go is a symlink to another file which matches a different formatter than the path of the symlink iself:

treefmt ./main.go
cat main.go | treefmt --stdin ./main.go

the first command (before and after this PR) follows the symlink and dispatches to formatter based on the path the symlink is pointing at

if we don't use resolvePath here, the second command would format based on the location of the symlink, not the file it is pointing at

The fallback is in case the path provided to --stdin is simply a hint, and does not point at an existing file.

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@adrian-gierakowski adrian-gierakowski Apr 5, 2026

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here's an implementation without the symlink resolution in case you want to try it for yourself:

adrian-gierakowski@9f74345

NOTE: I based this PR on last commit for which CI was green (CI failure here must be due to main being broken and github merging main into PR branch before running CI)

// We use the absolute path without resolving symlinks.
resolvedPath, err = filepath.Abs(path)
if err != nil {
return nil, fmt.Errorf("error computing absolute path of %s: %w", path, err)
}
}

relativePath, err := filepath.Rel(root, resolvedPath)
if err != nil {
return nil, fmt.Errorf("error computing relative path from %s to %s: %w", root, resolvedPath, err)
}

if strings.HasPrefix(path, "..") {
return nil, fmt.Errorf("path %s not inside the tree root %s", path, root)
if strings.HasPrefix(relativePath, "..") {
return nil, fmt.Errorf("path %s not inside the tree root %s (relative path: %s)", path, root, relativePath)
}

return NewStdinReader(root, path, statz), nil
return NewStdinReader(root, relativePath, statz), nil
}

// create a reader for each provided path
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