Add support for Chmod on billy.Filesystem

The billy package contains a `Change` interface type, which seems to
have gone unused for several years now, presumably due to the difficulty
of implementing most of the required methods for all supported
platforms.

This commit reduces the `Change` interface to a `Chmod` interface, which
is supported on all platforms. The interface is added to the main
`Filesystem` interface and implemented in all applicable abstractions.

Supporting `chmod` in billy would help with issues such as
go-git/go-git#588 (which was closed as stale,
but is unfortunately still a real issue for some folks).

Signed-off-by: Conrad Hoffmann <ch@bitfehler.net>

Author: bitfehler

embedfs/embed.go

@@ -92,6 +92,13 @@ func (fs *Embed) ReadDir(path string) ([]fs.DirEntry, error) {
 	return fs.underlying.ReadDir(path)
 }
 
+// Chmod is not supported.
+//
+// Calls will always return billy.ErrNotSupported.
+func (fs *Embed) Chmod(path string, mode fs.FileMode) error {
+	return billy.ErrNotSupported
+}
+
 // Chroot is not supported.
 //
 // Calls will always return billy.ErrNotSupported.

fs.go

@@ -4,7 +4,6 @@ import (
 	"errors"
 	"io"
 	"io/fs"
-	"time"
 )
 
 var (
@@ -58,6 +57,7 @@ type Filesystem interface {
 	TempFile
 	Dir
 	Symlink
+	Chmod
 	Chroot
 }
 
@@ -132,24 +132,12 @@ type Symlink interface {
 	Readlink(link string) (string, error)
 }
 
-// Change abstract the FileInfo change related operations in a storage-agnostic
+// Chmod abstract the FileInfo change related operations in a storage-agnostic
 // interface as an extension to the Basic interface
-type Change interface {
+type Chmod interface {
 	// Chmod changes the mode of the named file to mode. If the file is a
 	// symbolic link, it changes the mode of the link's target.
 	Chmod(name string, mode fs.FileMode) error
-	// Lchown changes the numeric uid and gid of the named file. If the file is
-	// a symbolic link, it changes the uid and gid of the link itself.
-	Lchown(name string, uid, gid int) error
-	// Chown changes the numeric uid and gid of the named file. If the file is a
-	// symbolic link, it changes the uid and gid of the link's target.
-	Chown(name string, uid, gid int) error
-	// Chtimes changes the access and modification times of the named file,
-	// similar to the Unix utime() or utimes() functions.
-	//
-	// The underlying filesystem may truncate or round the values to a less
-	// precise time unit.
-	Chtimes(name string, atime time.Time, mtime time.Time) error
 }
 
 // Chroot abstract the chroot related operations in a storage-agnostic interface

helper/chroot/chroot.go

@@ -201,6 +201,15 @@ func (fs *ChrootHelper) Readlink(link string) (string, error) {
 	return string(os.PathSeparator) + target, nil
 }
 
+func (fs *ChrootHelper) Chmod(path string, mode fs.FileMode) error {
+	fullpath, err := fs.underlyingPath(path)
+	if err != nil {
+		return err
+	}
+
+	return fs.underlying.(billy.Chmod).Chmod(fullpath, mode)
+}
+
 func (fs *ChrootHelper) Chroot(path string) (billy.Filesystem, error) {
 	fullpath, err := fs.underlyingPath(path)
 	if err != nil {

helper/polyfill/polyfill.go

@@ -14,7 +14,7 @@ type Polyfill struct {
 	c capabilities
 }
 
-type capabilities struct{ tempfile, dir, symlink, chroot bool }
+type capabilities struct{ tempfile, dir, symlink, chmod, chroot bool }
 
 // New creates a new filesystem wrapping up 'fs' the intercepts all the calls
 // made and errors if fs doesn't implement any of the billy interfaces.
@@ -28,6 +28,7 @@ func New(fs billy.Basic) billy.Filesystem {
 	_, h.c.tempfile = h.Basic.(billy.TempFile)
 	_, h.c.dir = h.Basic.(billy.Dir)
 	_, h.c.symlink = h.Basic.(billy.Symlink)
+	_, h.c.chmod = h.Basic.(billy.Chmod)
 	_, h.c.chroot = h.Basic.(billy.Chroot)
 	return h
 }
@@ -80,6 +81,14 @@ func (h *Polyfill) Lstat(path string) (os.FileInfo, error) {
 	return h.Basic.(billy.Symlink).Lstat(path)
 }
 
+func (h *Polyfill) Chmod(path string, mode fs.FileMode) error {
+	if !h.c.chmod {
+		return billy.ErrNotSupported
+	}
+
+	return h.Basic.(billy.Chmod).Chmod(path, mode)
+}
+
 func (h *Polyfill) Chroot(path string) (billy.Filesystem, error) {
 	if !h.c.chroot {
 		return nil, billy.ErrNotSupported

memfs/memory.go

@@ -177,6 +177,10 @@ func (fs *Memory) Remove(filename string) error {
 	return fs.s.Remove(filename)
 }
 
+func (fs *Memory) Chmod(path string, mode gofs.FileMode) error {
+	return fs.s.Chmod(path, mode)
+}
+
 // Falls back to Go's filepath.Join, which works differently depending on the
 // OS where the code is being executed.
 func (fs *Memory) Join(elem ...string) string {

memfs/storage.go

@@ -222,6 +222,18 @@ func (s *storage) Remove(path string) error {
 	return nil
 }
 
+func (s *storage) Chmod(path string, mode fs.FileMode) error {
+	path = clean(path)
+
+	f, has := s.Get(path)
+	if !has {
+		return os.ErrNotExist
+	}
+
+	f.mode = mode
+	return nil
+}
+
 func clean(path string) string {
 	return filepath.Clean(filepath.FromSlash(path))
 }

osfs/os_bound.go

@@ -226,6 +226,14 @@ func (fs *BoundOS) Readlink(link string) (string, error) {
 	return os.Readlink(link)
 }
 
+func (fs *BoundOS) Chmod(path string, mode fs.FileMode) error {
+	abspath, err := fs.abs(path)
+	if err != nil {
+		return err
+	}
+	return os.Chmod(abspath, mode)
+}
+
 // Chroot returns a new BoundOS filesystem, with the base dir set to the
 // result of joining the provided path with the underlying base dir.
 func (fs *BoundOS) Chroot(path string) (billy.Filesystem, error) {

osfs/os_chroot.go

@@ -80,6 +80,10 @@ func (fs *ChrootOS) Remove(filename string) error {
 	return os.Remove(filename)
 }
 
+func (fs *ChrootOS) Chmod(path string, mode fs.FileMode) error {
+	return os.Chmod(path, mode)
+}
+
 func (fs *ChrootOS) TempFile(dir, prefix string) (billy.File, error) {
 	if err := fs.createDir(dir + string(os.PathSeparator)); err != nil {
 		return nil, err