Index: Add ReadTree()

index.go

@@ -240,6 +240,20 @@ func (v *Index) WriteTreeTo(repo *Repository) (*Oid, error) {
 	return oid, nil
 }
 
+// ReadTree replaces the contents of the index with those of the given
+// tree
+func (v *Index) ReadTree(tree *Tree) error {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	ret := C.git_index_read_tree(v.ptr, tree.cast_ptr);
+	if ret < 0 {
+		return MakeGitError(ret)
+	}
+
+	return nil
+}
+
 func (v *Index) WriteTree() (*Oid, error) {
 	oid := new(Oid)
 

index_test.go

@@ -22,6 +22,34 @@ func TestCreateRepoAndStage(t *testing.T) {
 	}
 }
 
+func TestIndexReadTree(t *testing.T) {
+	repo := createTestRepo(t)
+	defer cleanupTestRepo(t, repo)
+
+	_, _ = seedTestRepo(t, repo)
+
+	ref, err := repo.Head()
+	checkFatal(t, err)
+
+	obj, err := ref.Peel(ObjectTree);
+	checkFatal(t, err)
+
+	tree := obj.(*Tree)
+
+	idx, err := NewIndex()
+	checkFatal(t, err)
+
+	err = idx.ReadTree(tree)
+	checkFatal(t, err)
+
+	id, err := idx.WriteTreeTo(repo)
+	checkFatal(t, err)
+
+	if tree.Id().Cmp(id) != 0 {
+		t.Fatalf("Read and written trees are not the same")
+	}
+}
+
 func TestIndexWriteTreeTo(t *testing.T) {
 	repo := createTestRepo(t)
 	defer cleanupTestRepo(t, repo)