Update embedfs implementation:

- Fix path normalization to support billy's absolute path convention ("/")
- Implement missing Lstat method (was returning ErrNotSupported)
- Add proper embed.FS to billy path conversion throughout all methods

Additional test coverage:
- Add dedicated test files for different functionality areas
- Test File interface methods including ReadAt, Close, Lock/Unlock
- Add path normalization and edge case testing
- Test empty file handling and boundary conditions
- Verify proper error handling for read-only operations

Test infrastructure:
- Create embedfs_testdata package for reusable test data
- Resolve import cycles with clean provider pattern
- Add test data including nested directories and various file types
- Organize tests by functionality (fs, dir, file operations)

The embedfs implementation now provides billy.Filesystem compliance
for read-only embedded filesystems.

Author: krrrke

embedfs/debug_test.go

@@ -0,0 +1,30 @@
+package embedfs
+
+import (
+	"embed"
+	"testing"
+
+	"github.com/go-git/go-billy/v6/embedfs_testdata"
+)
+
+var emptyEmbedFS embed.FS
+
+func TestDebugErrors(t *testing.T) {
+	// Test 1: Empty embed.FS with empty path
+	emptyFS := New(&emptyEmbedFS)
+	_, err1 := emptyFS.ReadDir("")
+	t.Logf("Empty FS, empty path: %v", err1)
+	
+	// Test 2: Empty embed.FS with root path
+	_, err2 := emptyFS.ReadDir("/")
+	t.Logf("Empty FS, root path: %v", err2)
+	
+	// Test 3: Non-empty embed.FS with empty path
+	richFS := New(embedfs_testdata.GetTestData())
+	_, err3 := richFS.ReadDir("")
+	t.Logf("Rich FS, empty path: %v", err3)
+	
+	// Test 4: Non-empty embed.FS with root path
+	entries, err4 := richFS.ReadDir("/")
+	t.Logf("Rich FS, root path: %d entries, err: %v", len(entries), err4)
+}

embedfs/dir_test.go

@@ -0,0 +1,63 @@
+package embedfs
+
+import (
+	"os"
+	"testing"
+
+	"github.com/go-git/go-billy/v6/embedfs_testdata"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// Directory operation tests adapted from test/dir_test.go for read-only embedfs
+
+func TestDir_ReadDirNested(t *testing.T) {
+	t.Parallel()
+
+	fs := New(embedfs_testdata.GetTestData())
+
+	// Test reading nested directories
+	entries, err := fs.ReadDir("/testdata/subdir")
+	require.NoError(t, err)
+	assert.Len(t, entries, 1)
+	assert.Equal(t, "nested.txt", entries[0].Name())
+	assert.False(t, entries[0].IsDir())
+}
+
+func TestDir_ReadDirFileInfo(t *testing.T) {
+	t.Parallel()
+
+	fs := New(embedfs_testdata.GetTestData())
+
+	entries, err := fs.ReadDir("/testdata")
+	require.NoError(t, err)
+	
+	// Verify all entries have proper FileInfo
+	for _, entry := range entries {
+		assert.NotEmpty(t, entry.Name())
+		assert.NotNil(t, entry.ModTime())
+		assert.Greater(t, entry.Size(), int64(-1)) // Size can be 0 but not negative
+	}
+}
+
+func TestDir_ReadDirFileInfoDirs(t *testing.T) {
+	t.Parallel()
+
+	fs := New(embedfs_testdata.GetTestData())
+
+	entries, err := fs.ReadDir("/testdata")
+	require.NoError(t, err)
+	
+	// Find the subdirectory entry
+	var subdirEntry os.FileInfo
+	for _, entry := range entries {
+		if entry.Name() == "subdir" {
+			subdirEntry = entry
+			break
+		}
+	}
+	
+	require.NotNil(t, subdirEntry, "subdir should be found")
+	assert.True(t, subdirEntry.IsDir(), "subdir should be a directory")
+	assert.Equal(t, "subdir", subdirEntry.Name())
+}

embedfs/embed.go

@@ -32,11 +32,26 @@ func New(efs *embed.FS) billy.Filesystem {
 	return fs
 }
 
+// normalizePath converts billy's absolute paths to embed.FS relative paths
+func (fs *Embed) normalizePath(path string) string {
+	// embed.FS uses "." for root directory, but billy uses "/"
+	if path == "/" {
+		return "."
+	}
+	// Remove leading slash for embed.FS
+	if strings.HasPrefix(path, "/") {
+		return path[1:]
+	}
+	return path
+}
+
 func (fs *Embed) Root() string {
 	return ""
 }
 
 func (fs *Embed) Stat(filename string) (os.FileInfo, error) {
+	filename = fs.normalizePath(filename)
+	
 	f, err := fs.underlying.Open(filename)
 	if err != nil {
 		return nil, err
@@ -53,6 +68,7 @@ func (fs *Embed) OpenFile(filename string, flag int, _ os.FileMode) (billy.File,
 		return nil, billy.ErrReadOnly
 	}
 
+	filename = fs.normalizePath(filename)
 	f, err := fs.underlying.Open(filename)
 	if err != nil {
 		return nil, err
@@ -91,6 +107,8 @@ func (fs *Embed) Join(elem ...string) string {
 }
 
 func (fs *Embed) ReadDir(path string) ([]os.FileInfo, error) {
+	path = fs.normalizePath(path)
+	
 	e, err := fs.underlying.ReadDir(path)
 	if err != nil {
 		return nil, err
@@ -114,11 +132,9 @@ func (fs *Embed) Chroot(_ string) (billy.Filesystem, error) {
 	return nil, billy.ErrNotSupported
 }
 
-// Lstat is not supported.
-//
-// Calls will always return billy.ErrNotSupported.
-func (fs *Embed) Lstat(_ string) (os.FileInfo, error) {
-	return nil, billy.ErrNotSupported
+// Lstat behaves the same as Stat for embedded filesystems since there are no symlinks.
+func (fs *Embed) Lstat(filename string) (os.FileInfo, error) {
+	return fs.Stat(filename)
 }
 
 // Readlink is not supported.