pkg/archive: remove backward compat hack for go < 1.9

The fillGo18FileTypeBits func was added in 1a451d9
to keep the tar headers consistent with headers created with go1.8 and older.

go1.8 and older incorrectly preserved all file-mode bits, including file-type,
instead of stripping those bits and only preserving the _permission_ bits, as
defined in;

- the GNU tar spec: https://www.gnu.org/software/tar/manual/html_node/Standard.html
- and POSIX: http://pubs.opengroup.org/onlinepubs/009695399/basedefs/tar.h.html

We decided at the time to copy the "wrong" behavior to prevent a cache-bust and
to keep the archives identical, however:

- It's not matching the standards, which causes differences between our tar
  implementation and the standard tar implementations, as well as implementations
  in other languages, such as Python (see docker/compose#883).
- BuildKit does not implement this hack.
- We don't _need_ this extra information (as it's already preserved in the
  type header; https://pkg.go.dev/archive/tar#pkg-constants

In short; let's remove this hack.

This reverts commit 1a451d9.
This reverts commit 41eb61d.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

pkg/archive/archive.go

@@ -99,16 +99,6 @@ const (
 	OverlayWhiteoutFormat
 )
 
-const (
-	modeISDIR  = 040000  // Directory
-	modeISFIFO = 010000  // FIFO
-	modeISREG  = 0100000 // Regular file
-	modeISLNK  = 0120000 // Symbolic link
-	modeISBLK  = 060000  // Block special file
-	modeISCHR  = 020000  // Character special file
-	modeISSOCK = 0140000 // Socket
-)
-
 // IsArchivePath checks if the (possibly compressed) file at the given path
 // starts with a tar file header.
 func IsArchivePath(path string) bool {
@@ -458,9 +448,7 @@ func FileInfoHeaderNoLookups(fi os.FileInfo, link string) (*tar.Header, error) {
 // but is safe to call from a chrooted process. The AccessTime and ChangeTime
 // fields are not set in the returned header, ModTime is truncated to one-second
 // precision, and the Uname and Gname fields are only set when fi is a FileInfo
-// value returned from tar.Header.FileInfo(). Also, regardless of Go version,
-// this function fills file type bits (e.g. hdr.Mode |= modeISDIR), which have
-// been deleted since Go 1.9 archive/tar.
+// value returned from tar.Header.FileInfo().
 func FileInfoHeader(name string, fi os.FileInfo, link string) (*tar.Header, error) {
 	hdr, err := FileInfoHeaderNoLookups(fi, link)
 	if err != nil {
@@ -470,36 +458,11 @@ func FileInfoHeader(name string, fi os.FileInfo, link string) (*tar.Header, erro
 	hdr.ModTime = hdr.ModTime.Truncate(time.Second)
 	hdr.AccessTime = time.Time{}
 	hdr.ChangeTime = time.Time{}
-	hdr.Mode = fillGo18FileTypeBits(int64(chmodTarEntry(os.FileMode(hdr.Mode))), fi)
+	hdr.Mode = int64(chmodTarEntry(os.FileMode(hdr.Mode)))
 	hdr.Name = canonicalTarName(name, fi.IsDir())
 	return hdr, nil
 }
 
-// fillGo18FileTypeBits fills type bits which have been removed on Go 1.9 archive/tar
-// https://github.com/golang/go/commit/66b5a2f
-func fillGo18FileTypeBits(mode int64, fi os.FileInfo) int64 {
-	fm := fi.Mode()
-	switch {
-	case fm.IsRegular():
-		mode |= modeISREG
-	case fi.IsDir():
-		mode |= modeISDIR
-	case fm&os.ModeSymlink != 0:
-		mode |= modeISLNK
-	case fm&os.ModeDevice != 0:
-		if fm&os.ModeCharDevice != 0 {
-			mode |= modeISCHR
-		} else {
-			mode |= modeISBLK
-		}
-	case fm&os.ModeNamedPipe != 0:
-		mode |= modeISFIFO
-	case fm&os.ModeSocket != 0:
-		mode |= modeISSOCK
-	}
-	return mode
-}
-
 // ReadSecurityXattrToTarHeader reads security.capability xattr from filesystem
 // to a tar header
 func ReadSecurityXattrToTarHeader(path string, hdr *tar.Header) error {

pkg/archive/archive_windows.go

@@ -31,14 +31,8 @@ func CanonicalTarNameForPath(p string) string {
 // chmodTarEntry is used to adjust the file permissions used in tar header based
 // on the platform the archival is done.
 func chmodTarEntry(perm os.FileMode) os.FileMode {
-	// perm &= 0755 // this 0-ed out tar flags (like link, regular file, directory marker etc.)
-	permPart := perm & os.ModePerm
-	noPermPart := perm &^ os.ModePerm
-	// Add the x bit: make everything +x from windows
-	permPart |= 0111
-	permPart &= 0755
-
-	return noPermPart | permPart
+	// Add the x bit: make everything +x on Windows
+	return perm | 0111
 }
 
 func setHeaderForSpecialDevice(hdr *tar.Header, name string, stat interface{}) (err error) {

pkg/archive/archive_windows_test.go

@@ -71,12 +71,10 @@ func TestChmodTarEntry(t *testing.T) {
 		in, expected os.FileMode
 	}{
 		{0000, 0111},
-		{0777, 0755},
+		{0777, 0777},
 		{0644, 0755},
 		{0755, 0755},
 		{0444, 0555},
-		{0755 | os.ModeDir, 0755 | os.ModeDir},
-		{0755 | os.ModeSymlink, 0755 | os.ModeSymlink},
 	}
 	for _, v := range cases {
 		if out := chmodTarEntry(v.in); out != v.expected {