plumbing: object, commit.Parent() method

plumbing/object/commit.go

@@ -3,6 +3,7 @@ package object
 import (
 	"bufio"
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
 	"strings"
@@ -91,6 +92,17 @@ func (c *Commit) NumParents() int {
 	return len(c.ParentHashes)
 }
 
+var ErrParentNotFound = errors.New("commit parent not found")
+
+// Parent returns the ith parent of a commit.
+func (c *Commit) Parent(i int) (*Commit, error) {
+	if len(c.ParentHashes) == 0 || i > len(c.ParentHashes)-1 {
+		return nil, ErrParentNotFound
+	}
+
+	return GetCommit(c.s, c.ParentHashes[i])
+}
+
 // File returns the file with the specified "path" in the commit and a
 // nil error if the file exists. If the file does not exist, it returns
 // a nil file and the ErrFileNotFound error.

plumbing/object/commit_test.go

@@ -67,6 +67,18 @@ func (s *SuiteCommit) TestParents(c *C) {
 	i.Close()
 }
 
+func (s *SuiteCommit) TestParent(c *C) {
+	commit, err := s.Commit.Parent(1)
+	c.Assert(err, IsNil)
+	c.Assert(commit.Hash.String(), Equals, "a5b8b09e2f8fcb0bb99d3ccb0958157b40890d69")
+}
+
+func (s *SuiteCommit) TestParentNotFound(c *C) {
+	commit, err := s.Commit.Parent(42)
+	c.Assert(err, Equals, ErrParentNotFound)
+	c.Assert(commit, IsNil)
+}
+
 func (s *SuiteCommit) TestPatch(c *C) {
 	from := s.commit(c, plumbing.NewHash("918c48b83bd081e863dbe1b80f8998f058cd8294"))
 	to := s.commit(c, plumbing.NewHash("6ecf0ef2c2dffb796033e5a02219af86ec6584e5"))