Fix tests

io/fs/disk.go

@@ -553,6 +553,51 @@ func (fs *diskFilesystem) List(path, pattern string) []FileInfo {
 	return files
 }
 
+func (fs *diskFilesystem) LookPath(file string) (string, error) {
+	if strings.Contains(file, "/") {
+		file = fs.cleanPath(file)
+		err := fs.findExecutable(file)
+		if err == nil {
+			return file, nil
+		}
+		return "", os.ErrNotExist
+	}
+	path := os.Getenv("PATH")
+	for _, dir := range filepath.SplitList(path) {
+		if dir == "" {
+			// Unix shell semantics: path element "" means "."
+			dir = "."
+		}
+		path := filepath.Join(dir, file)
+		path = fs.cleanPath(path)
+		if err := fs.findExecutable(path); err == nil {
+			if !filepath.IsAbs(path) {
+				return path, os.ErrNotExist
+			}
+			return path, nil
+		}
+	}
+	return "", os.ErrNotExist
+}
+
+func (fs *diskFilesystem) findExecutable(file string) error {
+	d, err := fs.Stat(file)
+	if err != nil {
+		return err
+	}
+
+	m := d.Mode()
+	if m.IsDir() {
+		return fmt.Errorf("is a directory")
+	}
+
+	if m&0111 != 0 {
+		return nil
+	}
+
+	return os.ErrPermission
+}
+
 func (fs *diskFilesystem) walk(path string, walkfn func(path string, info os.FileInfo)) {
 	filepath.Walk(path, func(path string, info os.FileInfo, err error) error {
 		if err != nil {

io/fs/fs.go

@@ -66,6 +66,12 @@ type ReadFilesystem interface {
 
 	// List lists all files that are currently on the filesystem.
 	List(path, pattern string) []FileInfo
+
+	// LookPath searches for an executable named file in the directories named by the PATH environment
+	// variable. If file contains a slash, it is tried directly and the PATH is not consulted. Otherwise,
+	// on success, the result is an absolute path. On non-disk filesystems. Only the mere existence
+	// of that file is verfied.
+	LookPath(file string) (string, error)
 }
 
 type WriteFilesystem interface {

io/fs/mem.go

@@ -697,6 +697,39 @@ func (fs *memFilesystem) List(path, pattern string) []FileInfo {
 	return files
 }
 
+func (fs *memFilesystem) LookPath(file string) (string, error) {
+	if strings.Contains(file, "/") {
+		file = fs.cleanPath(file)
+		info, err := fs.Stat(file)
+		if err == nil {
+			if !info.Mode().IsRegular() {
+				return file, os.ErrNotExist
+			}
+			return file, nil
+		}
+		return "", os.ErrNotExist
+	}
+	path := os.Getenv("PATH")
+	for _, dir := range filepath.SplitList(path) {
+		if dir == "" {
+			// Unix shell semantics: path element "" means "."
+			dir = "."
+		}
+		path := filepath.Join(dir, file)
+		path = fs.cleanPath(path)
+		if info, err := fs.Stat(path); err == nil {
+			if !filepath.IsAbs(path) {
+				return path, os.ErrNotExist
+			}
+			if !info.Mode().IsRegular() {
+				return path, os.ErrNotExist
+			}
+			return path, nil
+		}
+	}
+	return "", os.ErrNotExist
+}
+
 func (fs *memFilesystem) cleanPath(path string) string {
 	if !filepath.IsAbs(path) {
 		path = filepath.Join("/", path)

io/fs/s3.go

@@ -511,6 +511,39 @@ func (fs *s3Filesystem) List(path, pattern string) []FileInfo {
 	return files
 }
 
+func (fs *s3Filesystem) LookPath(file string) (string, error) {
+	if strings.Contains(file, "/") {
+		file = fs.cleanPath(file)
+		info, err := fs.Stat(file)
+		if err == nil {
+			if !info.Mode().IsRegular() {
+				return file, os.ErrNotExist
+			}
+			return file, nil
+		}
+		return "", os.ErrNotExist
+	}
+	path := os.Getenv("PATH")
+	for _, dir := range filepath.SplitList(path) {
+		if dir == "" {
+			// Unix shell semantics: path element "" means "."
+			dir = "."
+		}
+		path := filepath.Join(dir, file)
+		path = fs.cleanPath(path)
+		if info, err := fs.Stat(path); err == nil {
+			if !filepath.IsAbs(path) {
+				return path, os.ErrNotExist
+			}
+			if !info.Mode().IsRegular() {
+				return path, os.ErrNotExist
+			}
+			return path, nil
+		}
+	}
+	return "", os.ErrNotExist
+}
+
 func (fs *s3Filesystem) isDir(path string) bool {
 	if !strings.HasSuffix(path, "/") {
 		path = path + "/"