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[release-branch.go1.20] path/filepath: consider \\?\c: as a volume on Windows #64091

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[release-branch.go1.20] path/filepath: consider \\?\c: as a volume on Windows #64091

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15 changes: 10 additions & 5 deletions src/path/filepath/path_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -108,6 +108,8 @@ var wincleantests = []PathTest{
{`//abc`, `\\abc`},
{`///abc`, `\\\abc`},
{`//abc//`, `\\abc\\`},
{`\\?\C:\`, `\\?\C:\`},
{`\\?\C:\a`, `\\?\C:\a`},

// Don't allow cleaning to move an element with a colon to the start of the path.
{`a/../c:`, `.\c:`},
Expand Down Expand Up @@ -1472,10 +1474,13 @@ var volumenametests = []VolumeNameTest{
{`//.`, `\\.`},
{`//./`, `\\.\`},
{`//./NUL`, `\\.\NUL`},
{`//?/`, `\\?`},
{`//?`, `\\?`},
{`//?/`, `\\?\`},
{`//?/NUL`, `\\?\NUL`},
{`/??`, `\??`},
{`/??/`, `\??\`},
{`/??/NUL`, `\??\NUL`},
{`//./a/b`, `\\.\a`},
{`//?/`, `\\?`},
{`//?/`, `\\?`},
{`//./C:`, `\\.\C:`},
{`//./C:/`, `\\.\C:`},
{`//./C:/a/b/c`, `\\.\C:`},
Expand All @@ -1484,8 +1489,8 @@ var volumenametests = []VolumeNameTest{
{`//./UNC/host\`, `\\.\UNC\host\`},
{`//./UNC`, `\\.\UNC`},
{`//./UNC/`, `\\.\UNC\`},
{`\\?\x`, `\\?`},
{`\??\x`, `\??`},
{`\\?\x`, `\\?\x`},
{`\??\x`, `\??\x`},
}

func TestVolumeName(t *testing.T) {
Expand Down
20 changes: 7 additions & 13 deletions src/path/filepath/path_windows.go
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Original file line number Diff line number Diff line change
Expand Up @@ -102,12 +102,14 @@ func volumeNameLen(path string) int {
// \\.\unc\a\b\..\c into \\.\unc\a\c.
return uncLen(path, len(`\\.\UNC\`))

case pathHasPrefixFold(path, `\\.`):
// Path starts with \\., and is a Local Device path.
case pathHasPrefixFold(path, `\\.`) ||
pathHasPrefixFold(path, `\\?`) || pathHasPrefixFold(path, `\??`):
// Path starts with \\.\, and is a Local Device path; or
// path starts with \\?\ or \??\ and is a Root Local Device path.
//
// We currently treat the next component after the \\.\ prefix
// as part of the volume name, although there doesn't seem to be
// a principled reason to do this.
// We treat the next component after the \\.\ prefix as
// part of the volume name, which means Clean(`\\?\c:\`)
// won't remove the trailing \. (See #64028.)
if len(path) == 3 {
return 3 // exactly \\.
}
Expand All @@ -117,14 +119,6 @@ func volumeNameLen(path string) int {
}
return len(path) - len(rest) - 1

case pathHasPrefixFold(path, `\\?`) || pathHasPrefixFold(path, `\??`):
// Path starts with \\?\ or \??\, and is a Root Local Device path.
//
// While Windows usually treats / and \ as equivalent,
// /??/ does not seem to be recognized as a Root Local Device path.
// We treat it as one anyway here to be safe.
return 3

case len(path) >= 2 && isSlash(path[1]):
// Path starts with \\, and is a UNC path.
return uncLen(path, 2)
Expand Down