gitaly-git2go: Rebase skips commits upstream has

When a branch was partially merged into upstream, rebase should only
pick commits that are not in upstream.

This change uses merge base between the branch and upstream to determine
which commits do not yet exist in upstream. Only the descendant commits
from merge base are taken into account for the rebase.

2 files changed, 30 insertions, 1 deletions

diff --git a/cmd/gitaly-git2go/rebase.go b/cmd/gitaly-git2go/rebase.go
index ffb4630dd..3ca85cace 100644
--- a/cmd/gitaly-git2go/rebase.go
+++ b/cmd/gitaly-git2go/rebase.go
@@ -93,7 +93,12 @@ func (cmd *rebaseSubcommand) rebase(ctx context.Context, request *git2go.RebaseC
 		return onto.Id().String(), nil
 	}
 
-	rebase, err := repo.InitRebase(branch, onto, onto, &opts)
+	mergeCommit, err := repo.LookupAnnotatedCommit(mergeBase)
+	if err != nil {
+		return "", fmt.Errorf("look up merge base: %w", err)
+	}
+
+	rebase, err := repo.InitRebase(branch, mergeCommit, onto, &opts)
 	if err != nil {
 		return "", fmt.Errorf("initiate rebase: %w", err)
 	}
diff --git a/cmd/gitaly-git2go/rebase_test.go b/cmd/gitaly-git2go/rebase_test.go
index 45e63bc8d..899aaed63 100644
--- a/cmd/gitaly-git2go/rebase_test.go
+++ b/cmd/gitaly-git2go/rebase_test.go
@@ -8,6 +8,7 @@ import (
 
 	git "github.com/libgit2/git2go/v31"
 	"github.com/stretchr/testify/require"
+	cmdtesthelper "gitlab.com/gitlab-org/gitaly/cmd/gitaly-git2go/testhelper"
 	"gitlab.com/gitlab-org/gitaly/internal/git2go"
 	"gitlab.com/gitlab-org/gitaly/internal/testhelper"
 	"gitlab.com/gitlab-org/gitaly/internal/testhelper/testcfg"
@@ -69,6 +70,7 @@ func TestRebase_rebase(t *testing.T) {
 		desc         string
 		branch       string
 		commitsAhead int
+		setupRepo    func(testing.TB, *git.Repository)
 		expected     string
 	}{
 		{
@@ -94,6 +96,24 @@ func TestRebase_rebase(t *testing.T) {
 			branch:   "branch-merged",
 			expected: "1e292f8fedd741b75372e19097c76d327140c312",
 		},
+		{
+			desc:   "Partially merged branch",
+			branch: "branch-merged-plus-one",
+			setupRepo: func(t testing.TB, repo *git.Repository) {
+				head, err := lookupCommit(repo, "branch-merged")
+				require.NoError(t, err)
+
+				other, err := lookupCommit(repo, "gitaly-rename-test")
+				require.NoError(t, err)
+				tree, err := other.Tree()
+				require.NoError(t, err)
+				newOid, err := repo.CreateCommitFromIds("refs/heads/branch-merged-plus-one", &cmdtesthelper.DefaultAuthor, &cmdtesthelper.DefaultAuthor, "Message", tree.Object.Id(), head.Object.Id())
+				require.NoError(t, err)
+				require.Equal(t, "5da601ef10e314884bbade9d5b063be37579ccf9", newOid.String())
+			},
+			commitsAhead: 1,
+			expected:     "591b29084164bcc58fa4fb851a3c409290b17bfe",
+		},
 	}
 
 	for _, tc := range testcases {
@@ -111,6 +131,10 @@ func TestRebase_rebase(t *testing.T) {
 			repo, err := git.OpenRepository(repoPath)
 			require.NoError(t, err)
 
+			if tc.setupRepo != nil {
+				tc.setupRepo(t, repo)
+			}
+
 			request := git2go.RebaseCommand{
 				Repository:     repoPath,
 				Committer:      committer,