Add adapter to allow afero.Fs usage as io/fs.FS

It will not affect users of go older than 1.16 because files with `io/fs` import marked with build constraints

.travis.yml

@@ -7,6 +7,7 @@ arch:
 go:
   - "1.14"
   - "1.15"
+  - "1.16"
   - tip
 
 os:

README.md

@@ -33,7 +33,7 @@ filesystem for full interoperability.
 * Support for compositional (union) file systems by combining multiple file systems acting as one
 * Specialized backends which modify existing filesystems (Read Only, Regexp filtered)
 * A set of utility functions ported from io, ioutil & hugo to be afero aware
-
+* Wrapper for go 1.16 filesystem abstraction `io/fs.FS`
 
 # Using Afero
 

iofs.go

@@ -0,0 +1,138 @@
+// +build go1.16
+
+package afero
+
+import (
+	"io/fs"
+	"path"
+)
+
+// IOFS adopts afero.Fs to stdlib io/fs.FS
+type IOFS struct {
+	Fs
+}
+
+func NewIOFS(fs Fs) IOFS {
+	return IOFS{Fs: fs}
+}
+
+var (
+	_ fs.FS         = IOFS{}
+	_ fs.GlobFS     = IOFS{}
+	_ fs.ReadDirFS  = IOFS{}
+	_ fs.ReadFileFS = IOFS{}
+	_ fs.StatFS     = IOFS{}
+	_ fs.SubFS      = IOFS{}
+)
+
+func (iofs IOFS) Open(name string) (fs.File, error) {
+	const op = "open"
+
+	// by convention for fs.FS implementations we should perform this check
+	if !fs.ValidPath(name) {
+		return nil, iofs.wrapError(op, name, fs.ErrInvalid)
+	}
+
+	file, err := iofs.Fs.Open(name)
+	if err != nil {
+		return nil, iofs.wrapError(op, name, err)
+	}
+
+	// file should implement fs.ReadDirFile
+	if _, ok := file.(fs.ReadDirFile); !ok {
+		file = readDirFile{file}
+	}
+
+	return file, nil
+}
+
+func (iofs IOFS) Glob(pattern string) ([]string, error) {
+	const op = "glob"
+
+	// afero.Glob does not perform this check but it's required for implementations
+	if _, err := path.Match(pattern, ""); err != nil {
+		return nil, iofs.wrapError(op, pattern, err)
+	}
+
+	items, err := Glob(iofs.Fs, pattern)
+	if err != nil {
+		return nil, iofs.wrapError(op, pattern, err)
+	}
+
+	return items, nil
+}
+
+func (iofs IOFS) ReadDir(name string) ([]fs.DirEntry, error) {
+	items, err := ReadDir(iofs.Fs, name)
+	if err != nil {
+		return nil, iofs.wrapError("readdir", name, err)
+	}
+
+	ret := make([]fs.DirEntry, len(items))
+	for i := range items {
+		ret[i] = dirEntry{items[i]}
+	}
+
+	return ret, nil
+}
+
+func (iofs IOFS) ReadFile(name string) ([]byte, error) {
+	const op = "readfile"
+
+	if !fs.ValidPath(name) {
+		return nil, iofs.wrapError(op, name, fs.ErrInvalid)
+	}
+
+	bytes, err := ReadFile(iofs.Fs, name)
+	if err != nil {
+		return nil, iofs.wrapError(op, name, err)
+	}
+
+	return bytes, nil
+}
+
+func (iofs IOFS) Sub(dir string) (fs.FS, error) { return IOFS{NewBasePathFs(iofs.Fs, dir)}, nil }
+
+func (IOFS) wrapError(op, path string, err error) error {
+	if _, ok := err.(*fs.PathError); ok {
+		return err // don't need to wrap again
+	}
+
+	return &fs.PathError{
+		Op:   op,
+		Path: path,
+		Err:  err,
+	}
+}
+
+// dirEntry provides adapter from os.FileInfo to fs.DirEntry
+type dirEntry struct {
+	fs.FileInfo
+}
+
+var _ fs.DirEntry = dirEntry{}
+
+func (d dirEntry) Type() fs.FileMode { return d.FileInfo.Mode().Type() }
+
+func (d dirEntry) Info() (fs.FileInfo, error) { return d.FileInfo, nil }
+
+// readDirFile provides adapter from afero.File to fs.ReadDirFile needed for correct Open
+type readDirFile struct {
+	File
+}
+
+var _ fs.ReadDirFile = readDirFile{}
+
+func (r readDirFile) ReadDir(n int) ([]fs.DirEntry, error) {
+	items, err := r.File.Readdir(n)
+	if err != nil {
+		return nil, err
+	}
+
+	ret := make([]fs.DirEntry, len(items))
+	for i := range items {
+		ret[i] = dirEntry{items[i]}
+	}
+
+	return ret, nil
+}

iofs_test.go

@@ -0,0 +1,53 @@
+// +build go1.16
+
+package afero
+
+import (
+	"os"
+	"testing"
+	"testing/fstest"
+)
+
+func TestIOFS(t *testing.T) {
+	t.Parallel()
+
+	t.Run("use MemMapFs", func(t *testing.T) {
+		mmfs := NewMemMapFs()
+
+		err := mmfs.MkdirAll("dir1/dir2", os.ModePerm)
+		if err != nil {
+			t.Fatal("MkdirAll failed:", err)
+		}
+
+		f, err := mmfs.OpenFile("dir1/dir2/test.txt", os.O_RDWR|os.O_CREATE, os.ModePerm)
+		if err != nil {
+			t.Fatal("OpenFile (O_CREATE) failed:", err)
+		}
+
+		f.Close()
+
+		if err := fstest.TestFS(NewIOFS(mmfs), "dir1/dir2/test.txt"); err != nil {
+			t.Error(err)
+		}
+	})
+
+	t.Run("use OsFs", func(t *testing.T) {
+		osfs := NewBasePathFs(NewOsFs(), t.TempDir())
+
+		err := osfs.MkdirAll("dir1/dir2", os.ModePerm)
+		if err != nil {
+			t.Fatal("MkdirAll failed:", err)
+		}
+
+		f, err := osfs.OpenFile("dir1/dir2/test.txt", os.O_RDWR|os.O_CREATE, os.ModePerm)
+		if err != nil {
+			t.Fatal("OpenFile (O_CREATE) failed:", err)
+		}
+
+		f.Close()
+
+		if err := fstest.TestFS(NewIOFS(osfs), "dir1/dir2/test.txt"); err != nil {
+			t.Error(err)
+		}
+	})
+}