2 files changed, 76 insertions, 1 deletions

diff --git a/cmd/gitaly-git2go/merge.go b/cmd/gitaly-git2go/merge.go
index 907e717c0..dc9efd808 100644
--- a/cmd/gitaly-git2go/merge.go
+++ b/cmd/gitaly-git2go/merge.go
@@ -12,6 +12,7 @@ import (
 	"time"
 
 	git "github.com/libgit2/git2go/v30"
+	"gitlab.com/gitlab-org/gitaly/cmd/gitaly-git2go/conflicts"
 	"gitlab.com/gitlab-org/gitaly/internal/git2go"
 )
 
@@ -64,7 +65,13 @@ func (cmd *mergeSubcommand) Run(context.Context, io.Reader, io.Writer) error {
 	defer index.Free()
 
 	if index.HasConflicts() {
-		return errors.New("could not auto-merge due to conflicts")
+		if !request.AllowConflicts {
+			return errors.New("could not auto-merge due to conflicts")
+		}
+
+		if err := resolveConflicts(repo, index); err != nil {
+			return fmt.Errorf("could not resolve conflicts: %w", err)
+		}
 	}
 
 	tree, err := index.WriteTreeTo(repo)
@@ -88,3 +95,68 @@ func (cmd *mergeSubcommand) Run(context.Context, io.Reader, io.Writer) error {
 
 	return nil
 }
+
+func resolveConflicts(repo *git.Repository, index *git.Index) error {
+	// We need to get all conflicts up front as resolving conflicts as we
+	// iterate breaks the iterator.
+	indexConflicts, err := getConflicts(index)
+	if err != nil {
+		return err
+	}
+
+	for _, conflict := range indexConflicts {
+		merge, err := conflicts.Merge(repo, conflict)
+		if err != nil {
+			return err
+		}
+
+		mergedBlob, err := repo.CreateBlobFromBuffer(merge.Contents)
+		if err != nil {
+			return err
+		}
+
+		mergedIndexEntry := git.IndexEntry{
+			Path: merge.Path,
+			Mode: git.Filemode(merge.Mode),
+			Id:   mergedBlob,
+		}
+
+		if err := index.Add(&mergedIndexEntry); err != nil {
+			return err
+		}
+
+		if err := index.RemoveConflict(merge.Path); err != nil {
+			return err
+		}
+	}
+
+	if index.HasConflicts() {
+		return errors.New("index still has conflicts")
+	}
+
+	return nil
+}
+
+func getConflicts(index *git.Index) ([]git.IndexConflict, error) {
+	var conflicts []git.IndexConflict
+
+	iterator, err := index.ConflictIterator()
+	if err != nil {
+		return nil, err
+	}
+	defer iterator.Free()
+
+	for {
+		conflict, err := iterator.Next()
+		if err != nil {
+			if git.IsErrorCode(err, git.ErrIterOver) {
+				break
+			}
+			return nil, err
+		}
+
+		conflicts = append(conflicts, conflict)
+	}
+
+	return conflicts, nil
+}
diff --git a/internal/git2go/merge.go b/internal/git2go/merge.go
index 7659930a1..e92856810 100644
--- a/internal/git2go/merge.go
+++ b/internal/git2go/merge.go
@@ -37,6 +37,9 @@ type MergeCommand struct {
 	Ours string `json:"ours"`
 	// Theirs is the commit into which ours is to be merged.
 	Theirs string `json:"theirs"`
+	// AllowConflicts controls whether conflicts are allowed. If they are,
+	// then conflicts will be committed as part of the result.
+	AllowConflicts bool `json:"allow_conflicts"`
 }
 
 // MergeResult contains results from a merge.