contenthash: clear ModeIrregular before sending to archive/tar

Clears ModeIrregular from the checksum generation. This may be sent by
the client when the version of Go used is post Go 1.23. The behavior of
`os.Stat` was modified in Go 1.23 to set `ModeIrregular` on reparse
points in Windows. This clears `ModeIrregular` when any mode is set
which was the previous behavior of `os.Stat`.

Signed-off-by: Jonathan A. Sternberg <[email protected]>

Author: jsternberg

cache/contenthash/filehash.go

@@ -43,6 +43,14 @@ func NewFileHash(path string, fi os.FileInfo) (hash.Hash, error) {
 func NewFromStat(stat *fstypes.Stat) (hash.Hash, error) {
 	// Clear the socket bit since archive/tar.FileInfoHeader does not handle it
 	stat.Mode &^= uint32(os.ModeSocket)
+	if stat.Mode&uint32(os.ModeType) != 0 {
+		// Pre-Go 1.23 the mode of unknown reparse points on Windows would be set to
+		// zero and treated as a normal file. The behavior has changed so any reparse
+		// point that is not a unix socket, symlink, or dedup will cause ModeIrregular
+		// to be set. This restores the previous behavior to avoid an error from
+		// archive/tar.
+		stat.Mode &^= uint32(os.ModeIrregular)
+	}
 
 	fi := &statInfo{stat}
 	hdr, err := tar.FileInfoHeader(fi, stat.Linkname)