fix(mfs): Directory.Path not working, add test

Credit goes to @ridewindx

License: MIT
Signed-off-by: Jakub Sztandera <kubuxu@protonmail.ch>

mfs/dir.go

@@ -404,8 +404,15 @@ func (d *Directory) Path() string {
 	cur := d
 	var out string
 	for cur != nil {
-		out = path.Join(cur.name, out)
-		cur = cur.parent.(*Directory)
+		switch parent := cur.parent.(type) {
+		case *Directory:
+			out = path.Join(cur.name, out)
+			cur = parent
+		case *Root:
+			return "/" + out
+		default:
+			panic("directory parent neither a directory nor a root")
+		}
 	}
 	return out
 }

mfs/mfs_test.go

@@ -324,6 +324,11 @@ func TestDirectoryLoadFromDag(t *testing.T) {
 
 	topd := topi.(*Directory)
 
+	path := topd.Path()
+	if path != "/foo" {
+		t.Fatalf("Expected path '/foo', got '%s'", path)
+	}
+
 	// mkdir over existing but unloaded child file should fail
 	_, err = topd.Mkdir("a")
 	if err == nil {