ref: Handle `git.ErrReferenceAmbiguous` in `FindBranch`

The `repo.GetReference` can throw a `git.ErrReferenceAmbiguous` error
when the provided reference is ambiguous. We shouldn't treat these
errors as internal errors as they would then be counted towards the
error budget. So catch these errors and treat them as
`NewInvalidArgument` errors.

2 files changed, 13 insertions, 1 deletions

diff --git a/internal/gitaly/service/ref/branches.go b/internal/gitaly/service/ref/branches.go
index d67b18cec..8bfa08e72 100644
--- a/internal/gitaly/service/ref/branches.go
+++ b/internal/gitaly/service/ref/branches.go
@@ -26,6 +26,11 @@ func (s *server) FindBranch(ctx context.Context, req *gitalypb.FindBranchRequest
 		if errors.Is(err, git.ErrReferenceNotFound) {
 			return &gitalypb.FindBranchResponse{}, nil
 		}
+
+		if errors.Is(err, git.ErrReferenceAmbiguous) {
+			return nil, structerr.NewInvalidArgument("target reference is ambiguous: %w", err)
+		}
+
 		return nil, err
 	}
 	commit, err := repo.ReadCommit(ctx, git.Revision(branchRef.Target))
diff --git a/internal/gitaly/service/ref/branches_test.go b/internal/gitaly/service/ref/branches_test.go
index 393e44552..318f27708 100644
--- a/internal/gitaly/service/ref/branches_test.go
+++ b/internal/gitaly/service/ref/branches_test.go
@@ -87,7 +87,8 @@ func TestFailedFindBranchRequest(t *testing.T) {
 
 	ctx := testhelper.Context(t)
 	cfg, client := setupRefService(t)
-	repo, _ := gittest.CreateRepository(t, ctx, cfg)
+	repo, repoPath := gittest.CreateRepository(t, ctx, cfg)
+	gittest.WriteCommit(t, cfg, repoPath, gittest.WithBranch("branch"), gittest.WithMessage("branch"))
 
 	testCases := []struct {
 		desc        string
@@ -106,6 +107,12 @@ func TestFailedFindBranchRequest(t *testing.T) {
 			branchName:  "",
 			expectedErr: status.Error(codes.InvalidArgument, "Branch name cannot be empty"),
 		},
+		{
+			desc:        "ambiguous branch name",
+			repo:        repo,
+			branchName:  "b*",
+			expectedErr: structerr.NewInvalidArgument(`target reference is ambiguous: reference is ambiguous: conflicts with "refs/heads/branch"`),
+		},
 	}
 
 	for _, testCase := range testCases {