Add function to resolve short commit ID to full SHA1 (#122)

* Add function to resolve short commit ID to full SHA1

* Add tests for GetFullCommitID

commit.go

@@ -274,3 +274,19 @@ func (c *Commit) GetSubModule(entryname string) (*SubModule, error) {
 	}
 	return nil, nil
 }
+
+// GetFullCommitID returns full length (40) of commit ID by given short SHA in a repository.
+func GetFullCommitID(repoPath, shortID string) (string, error) {
+	if len(shortID) >= 40 {
+		return shortID, nil
+	}
+
+	commitID, err := NewCommand("rev-parse", shortID).RunInDir(repoPath)
+	if err != nil {
+		if strings.Contains(err.Error(), "exit status 128") {
+			return "", ErrNotExist{shortID, ""}
+		}
+		return "", err
+	}
+	return strings.TrimSpace(commitID), nil
+}

commit_test.go

@@ -14,3 +14,17 @@ func TestCommitsCount(t *testing.T) {
 	commitsCount, _ := CommitsCount(".", "d86a90f801dbe279db095437a8c7ea42c60e8d98")
 	assert.Equal(t, int64(3), commitsCount)
 }
+
+func TestGetFullCommitID(t *testing.T) {
+	id, err := GetFullCommitID(".", "d86a90f8")
+	assert.NoError(t, err)
+	assert.Equal(t, "d86a90f801dbe279db095437a8c7ea42c60e8d98", id)
+}
+
+func TestGetFullCommitIDError(t *testing.T) {
+	id, err := GetFullCommitID(".", "unknown")
+	assert.Empty(t, id)
+	if assert.Error(t, err) {
+		assert.EqualError(t, err, "object does not exist [id: unknown, rel_path: ]")
+	}
+}