operations: Provide conflicting commits on merge conflict error

The structured `MergeConflictError` provides information about the files
that have been conflicting, but it doesn't provide any information about
the revisions that caused the merge conflict. While that info should in
the general case already be available on the calling-side, it may not
necessarily be in case the caller e.g. only specified branch names
instead of commit IDs.

Add a new `ConflictingCommitIDs` field to the message that contains the
object IDs of the conflicting commits to provide additional context.

7 files changed, 82 insertions, 46 deletions

diff --git a/internal/gitaly/service/operations/rebase.go b/internal/gitaly/service/operations/rebase.go
index 9727f5dca..8e1340fce 100644
--- a/internal/gitaly/service/operations/rebase.go
+++ b/internal/gitaly/service/operations/rebase.go
@@ -82,6 +82,10 @@ func (s *Server) UserRebaseConfirmable(stream gitalypb.OperationService_UserReba
 						Error: &gitalypb.UserRebaseConfirmableError_RebaseConflict{
 							RebaseConflict: &gitalypb.MergeConflictError{
 								ConflictingFiles: conflictingFiles,
+								ConflictingCommitIds: []string{
+									startRevision.String(),
+									oldrev.String(),
+								},
 							},
 						},
 					},
diff --git a/internal/gitaly/service/operations/rebase_test.go b/internal/gitaly/service/operations/rebase_test.go
index 7842906d5..b1d1f5ce8 100644
--- a/internal/gitaly/service/operations/rebase_test.go
+++ b/internal/gitaly/service/operations/rebase_test.go
@@ -593,13 +593,14 @@ func testFailedUserRebaseConfirmableDueToGitError(t *testing.T, ctx context.Cont
 		Seed: gittest.SeedGitLabTest,
 	})
 
-	failedBranchName := "rebase-encoding-failure-trigger"
-	branchSha := getBranchSha(t, cfg, repoPath, failedBranchName)
+	targetBranch := "rebase-encoding-failure-trigger"
+	targetBranchCommitID := getBranchSha(t, cfg, repoPath, targetBranch)
+	sourceBranchCommitID := getBranchSha(t, cfg, repoPath, "master")
 
 	rebaseStream, err := client.UserRebaseConfirmable(ctx)
 	require.NoError(t, err)
 
-	headerRequest := buildHeaderRequest(repoProto, gittest.TestUser, "1", failedBranchName, branchSha, repoCopyProto, "master")
+	headerRequest := buildHeaderRequest(repoProto, gittest.TestUser, "1", targetBranch, targetBranchCommitID, repoCopyProto, "master")
 
 	require.NoError(t, rebaseStream.Send(headerRequest), "send header")
 
@@ -610,7 +611,13 @@ func testFailedUserRebaseConfirmableDueToGitError(t *testing.T, ctx context.Cont
 			&gitalypb.UserRebaseConfirmableError{
 				Error: &gitalypb.UserRebaseConfirmableError_RebaseConflict{
 					RebaseConflict: &gitalypb.MergeConflictError{
-						ConflictingFiles: [][]byte{[]byte("README.md")},
+						ConflictingFiles: [][]byte{
+							[]byte("README.md"),
+						},
+						ConflictingCommitIds: []string{
+							sourceBranchCommitID,
+							targetBranchCommitID,
+						},
 					},
 				},
 			},
@@ -623,8 +630,8 @@ func testFailedUserRebaseConfirmableDueToGitError(t *testing.T, ctx context.Cont
 		require.Equal(t, io.EOF, err)
 	}
 
-	newBranchSha := getBranchSha(t, cfg, repoPath, failedBranchName)
-	require.Equal(t, branchSha, newBranchSha, "branch should not change when the rebase fails due to GitError")
+	newBranchSha := getBranchSha(t, cfg, repoPath, targetBranch)
+	require.Equal(t, targetBranchCommitID, newBranchSha, "branch should not change when the rebase fails due to GitError")
 }
 
 func getBranchSha(t *testing.T, cfg config.Cfg, repoPath string, branchName string) string {
diff --git a/internal/gitaly/service/operations/squash.go b/internal/gitaly/service/operations/squash.go
index e34224b87..ccc875628 100644
--- a/internal/gitaly/service/operations/squash.go
+++ b/internal/gitaly/service/operations/squash.go
@@ -175,6 +175,10 @@ func (s *Server) userSquash(ctx context.Context, req *gitalypb.UserSquashRequest
 					Error: &gitalypb.UserSquashError_RebaseConflict{
 						RebaseConflict: &gitalypb.MergeConflictError{
 							ConflictingFiles: conflictingFiles,
+							ConflictingCommitIds: []string{
+								startCommit.String(),
+								endCommit.String(),
+							},
 						},
 					},
 				},
diff --git a/internal/gitaly/service/operations/squash_test.go b/internal/gitaly/service/operations/squash_test.go
index f19df0470..72d741ac1 100644
--- a/internal/gitaly/service/operations/squash_test.go
+++ b/internal/gitaly/service/operations/squash_test.go
@@ -637,6 +637,10 @@ func TestUserSquash_conflicts(t *testing.T) {
 					ConflictingFiles: [][]byte{
 						[]byte("b"),
 					},
+					ConflictingCommitIds: []string{
+						theirs.String(),
+						ours.String(),
+					},
 				},
 			},
 		},
diff --git a/proto/errors.proto b/proto/errors.proto
index 59d55cc63..2e4ccd5db 100644
--- a/proto/errors.proto
+++ b/proto/errors.proto
@@ -48,6 +48,9 @@ message MergeConflictError {
   // field is empty, then there has still been a merge conflict, but it wasn't
   // able to determine which files have been conflicting.
   repeated bytes conflicting_files = 1;
+  // ConflictingCommitIds is the set of commit IDs that caused the conflict. In the general case,
+  // this should be set to two commit IDs.
+  repeated string conflicting_commit_ids = 2;
 }
 
 // ReferencesLockedError is an error returned when an ref update fails because
diff --git a/proto/go/gitalypb/errors.pb.go b/proto/go/gitalypb/errors.pb.go
index 8a397eb4a..026bd7985 100644
--- a/proto/go/gitalypb/errors.pb.go
+++ b/proto/go/gitalypb/errors.pb.go
@@ -324,6 +324,9 @@ type MergeConflictError struct {
 	// field is empty, then there has still been a merge conflict, but it wasn't
 	// able to determine which files have been conflicting.
 	ConflictingFiles [][]byte `protobuf:"bytes,1,rep,name=conflicting_files,json=conflictingFiles,proto3" json:"conflicting_files,omitempty"`
+	// ConflictingCommitIds is the set of commit IDs that caused the conflict. In the general case,
+	// this should be set to two commit IDs.
+	ConflictingCommitIds []string `protobuf:"bytes,2,rep,name=conflicting_commit_ids,json=conflictingCommitIds,proto3" json:"conflicting_commit_ids,omitempty"`
 }
 
 func (x *MergeConflictError) Reset() {
@@ -365,6 +368,13 @@ func (x *MergeConflictError) GetConflictingFiles() [][]byte {
 	return nil
 }
 
+func (x *MergeConflictError) GetConflictingCommitIds() []string {
+	if x != nil {
+		return x.ConflictingCommitIds
+	}
+	return nil
+}
+
 // ReferencesLockedError is an error returned when an ref update fails because
 // the references have already been locked by another process.
 type ReferencesLockedError struct {
@@ -675,50 +685,53 @@ var file_errors_proto_rawDesc = []byte{
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+	0x0a, 0x14, 0x48, 0x4f, 0x4f, 0x4b, 0x5f, 0x54, 0x59, 0x50, 0x45, 0x5f, 0x50, 0x52, 0x45, 0x52,
+	0x45, 0x43, 0x45, 0x49, 0x56, 0x45, 0x10, 0x01, 0x12, 0x14, 0x0a, 0x10, 0x48, 0x4f, 0x4f, 0x4b,
+	0x5f, 0x54, 0x59, 0x50, 0x45, 0x5f, 0x55, 0x50, 0x44, 0x41, 0x54, 0x45, 0x10, 0x02, 0x12, 0x19,
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+	0x6c, 0x61, 0x62, 0x2e, 0x63, 0x6f, 0x6d, 0x2f, 0x67, 0x69, 0x74, 0x6c, 0x61, 0x62, 0x2d, 0x6f,
+	0x72, 0x67, 0x2f, 0x67, 0x69, 0x74, 0x61, 0x6c, 0x79, 0x2f, 0x76, 0x31, 0x35, 0x2f, 0x70, 0x72,
+	0x6f, 0x74, 0x6f, 0x2f, 0x67, 0x6f, 0x2f, 0x67, 0x69, 0x74, 0x61, 0x6c, 0x79, 0x70, 0x62, 0x62,
+	0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
 }
 
 var (
diff --git a/ruby/proto/gitaly/errors_pb.rb b/ruby/proto/gitaly/errors_pb.rb
index 2c069a5d8..42bf8b20e 100644
--- a/ruby/proto/gitaly/errors_pb.rb
+++ b/ruby/proto/gitaly/errors_pb.rb
@@ -23,6 +23,7 @@ Google::Protobuf::DescriptorPool.generated_pool.build do
     end
     add_message "gitaly.MergeConflictError" do
       repeated :conflicting_files, :bytes, 1
+      repeated :conflicting_commit_ids, :string, 2
     end
     add_message "gitaly.ReferencesLockedError" do
     end