adds Tree method to Tree

plumbing/object/tree.go

@@ -24,8 +24,9 @@ const (
 
 // New errors defined by this package.
 var (
-	ErrMaxTreeDepth = errors.New("maximum tree depth exceeded")
-	ErrFileNotFound = errors.New("file not found")
+	ErrMaxTreeDepth      = errors.New("maximum tree depth exceeded")
+	ErrFileNotFound      = errors.New("file not found")
+	ErrDirectoryNotFound = errors.New("directory not found")
 )
 
 // Tree is basically like a directory - it references a bunch of other trees
@@ -82,6 +83,17 @@ func (t *Tree) File(path string) (*File, error) {
 	return NewFile(path, e.Mode, blob), nil
 }
 
+// Tree returns the tree identified by the `path` argument.
+// The path is interpreted as relative to the tree receiver.
+func (t *Tree) Tree(path string) (*Tree, error) {
+	e, err := t.findEntry(path)
+	if err != nil {
+		return nil, ErrDirectoryNotFound
+	}
+
+	return GetTree(t.s, e.Hash)
+}
+
 // TreeEntryFile returns the *File for a given *TreeEntry.
 func (t *Tree) TreeEntryFile(e *TreeEntry) (*File, error) {
 	blob, err := GetBlob(t.s, e.Hash)

plumbing/object/tree_test.go

@@ -48,6 +48,22 @@ func (s *TreeSuite) TestType(c *C) {
 	c.Assert(s.Tree.Type(), Equals, plumbing.TreeObject)
 }
 
+func (s *TreeSuite) TestTree(c *C) {
+	expectedEntry, ok := s.Tree.m["vendor"]
+	c.Assert(ok, Equals, true)
+	expected := expectedEntry.Hash
+
+	obtainedTree, err := s.Tree.Tree("vendor")
+	c.Assert(err, IsNil)
+	c.Assert(obtainedTree.Hash, Equals, expected)
+}
+
+func (s *TreeSuite) TestTreeNotFound(c *C) {
+	d, err := s.Tree.Tree("not-found")
+	c.Assert(d, IsNil)
+	c.Assert(err, Equals, ErrDirectoryNotFound)
+}
+
 func (s *TreeSuite) TestFile(c *C) {
 	f, err := s.Tree.File("LICENSE")
 	c.Assert(err, IsNil)