Go (Golang) - fs.FS implementation with a correct root directory, using default os.Open implementation, as opposed to os.DirFS("/"), which can produce unwanted behavior on some systems

fs_impl_with_os_open.go

// issue in context: https://github.com/golang/go/issues/44279#issuecomment-1159714960

type OsFilesystem struct{}

func (f *OsFilesystem) Open(name string) (fs.File, error) {
	return os.Open(name)
}

// *OsFilesystem implements fs.FS
var _ fs.FS = new(OsFilesystem)


func TestOsFilesystem(t *testing.T) {
	// given
	openFile := func(fsys fs.FS, path string) error {
		_, err := fsys.Open(path)
		return err
	}

	fsys := new(OsFilesystem)

	t.Run("exists", func(t *testing.T) {
		// given
		path := "/tmp/existent.file"

		// when
		err := openFile(fsys, path)

		// then
		assert.NoError(t, err)
	})

	t.Run("does not exist", func(t *testing.T) {
		// given
		path := "/tmp/nonexistent.file"

		// when
		err := openFile(fsys, path)

		// then
		assert.Error(t, err)
		assert.True(t, errors.Is(err, fs.ErrNotExist))
	})
}