Make bff work with nonlinear history (#11)

Make bff work with nonlinear historyWhen I tried to create a new release for bff, `bff bump` failed because 5f0c3f8 has two parents: 3200804, and b31bdf7.
This fix finds the parent that gets committed the most recently.

### Test plan
`bff bump` runs successfully, updating the `VERSION` file.

cmd/bump.go

@@ -112,15 +112,11 @@ var bumpCmd = &cobra.Command{
 				break
 			}
 
-			if len(commit.ParentHashes) > 1 {
-				log.Fatal("bff only works with linear history")
-			}
-
 			if len(commit.ParentHashes) == 0 {
 				// When we get here we should be at the beginning of this repo's history
 				break
 			}
-			commit, err = commit.Parent(0)
+			commit, err = util.GetLatestParentCommit(commit)
 			if err != nil {
 				log.Fatal(err)
 			}
@@ -161,15 +157,11 @@ var bumpCmd = &cobra.Command{
 				feature = true
 			}
 
-			if len(commit.ParentHashes) > 1 {
-				log.Fatal("bff only works with linear history")
-			}
-
 			if len(commit.ParentHashes) == 0 {
 				// When we get here we should be at the beginning of this repo's history
 				break
 			}
-			commit, err = commit.Parent(0)
+			commit, err = util.GetLatestParentCommit(commit)
 			if err != nil {
 				log.Fatal(err)
 			}
@@ -234,7 +226,7 @@ var bumpCmd = &cobra.Command{
 	},
 }
 
-//  ReleaseType will calculate whether the next release should be major, minor or patch
+// ReleaseType will calculate whether the next release should be major, minor or patch
 func ReleaseType(major uint64, breaking, feature bool) string {
 	if major < 1 {
 		if breaking || feature {
@@ -252,6 +244,7 @@ func ReleaseType(major uint64, breaking, feature bool) string {
 	}
 }
 
+// NewVersion returns the next version based on the current version and next release type
 func NewVersion(ver semver.Version, releaseType string) semver.Version {
 	switch releaseType {
 	case "major":

pkg/util/git.go

@@ -10,6 +10,7 @@ import (
 	"gopkg.in/src-d/go-git.v4/plumbing/storer"
 
 	"github.com/pkg/errors"
+	log "github.com/sirupsen/logrus"
 )
 
 // GetGitAuthor returns the author name and email
@@ -60,7 +61,6 @@ func LatestTagCommitHash(repo *git.Repository) (*string, *plumbing.Hash, error)
 	}
 
 	err = tags.ForEach(func(tag *plumbing.Reference) error {
-		// logrus.Infof("Visiting tag %s", tag.Name().String())
 		tagIndex[tag.Hash().String()] = strings.Replace(tag.Name().String(), "refs/tags/v", "", -1)
 		return nil
 	})
@@ -82,16 +82,11 @@ func LatestTagCommitHash(repo *git.Repository) (*string, *plumbing.Hash, error)
 
 	err = gitLog.ForEach(func(c *object.Commit) error {
 		if v, ok := tagIndex[c.Hash.String()]; ok {
-			// logrus.Warnf("Found tag %s; break", v)
 			latestVersionTag = v
 			latestVersionHash = c.Hash
 			return storer.ErrStop
 		}
 
-		if len(c.ParentHashes) > 1 {
-			return errors.New("bff only works with linear history")
-		}
-
 		if len(c.ParentHashes) == 0 {
 			// When we get here we should be at the beginning of the history
 			return storer.ErrStop
@@ -101,3 +96,21 @@ func LatestTagCommitHash(repo *git.Repository) (*string, *plumbing.Hash, error)
 	return &latestVersionTag, &latestVersionHash, errors.Wrap(err, "error searching git history for latest tag")
 
 }
+
+// GetLatestParentCommit returns the most recent parent commit
+func GetLatestParentCommit(commit *object.Commit) (*object.Commit, error) {
+	var recentParentCommit *object.Commit
+	if commit.NumParents() > 1 {
+		log.Warnf("Commit %s has more than 1 parent", commit.Hash.String())
+	}
+	for i := 0; i < commit.NumParents(); i++ {
+		currentParentCommit, err := commit.Parent(i)
+		if err != nil {
+			return recentParentCommit, errors.Wrap(err, "unable to retrieve a parent hash")
+		}
+		if i == 0 || currentParentCommit.Author.When.After(recentParentCommit.Author.When) {
+			recentParentCommit = currentParentCommit
+		}
+	}
+	return recentParentCommit, nil
+}