operations: Use structured errors in UserDeleteBranchpks-user-delete-branch-structured-errors

UserDeleteBranch is returning successfully in some error cases. This is
a pattern we want to get rid of, so let's convert the RPC to instead use
the structured errors via the new `UserDeleteBranchError` message type.

This fixes some cases where we know to create replication jobs because
the `UserDeleteBranch` RPC returns successfully, but didn't cast a
single vote.

Changelog: fixed

2 files changed, 24 insertions, 9 deletions

diff --git a/proto/go/gitalypb/operations_grpc.pb.go b/proto/go/gitalypb/operations_grpc.pb.go
index 3ee7dabeb..0171226c2 100644
--- a/proto/go/gitalypb/operations_grpc.pb.go
+++ b/proto/go/gitalypb/operations_grpc.pb.go
@@ -28,9 +28,14 @@ type OperationServiceClient interface {
 	//
 	// - Returns `InvalidArgument` in case either the branch name or user are not set.
 	// - Returns `FailedPrecondition` in case the branch does not exist.
-	// - Returns `OK` with a `PreReceiveError` in case custom hooks refused the update.
-	// - Returns `FailedPrecondition` in case updating the reference fails because of a concurrent
-	//   write to the same reference.
+	// - Returns `OK` with a `PreReceiveError` in case custom hooks refused the update. If the
+	//   `gitaly_user_delete_branch_structured_errors` feature flag is enabled this error case will
+	//   instead return `PermissionDenied` with either a `CustomHook` or AccessCheck` structured
+	//   error.
+	// - Returns `FailedPrecondition` in case updating the reference fails because
+	//   of a concurrent write to the same reference. If the
+	//   `gitaly_user_delete_branch_structured_errors` feature flag is set this error case will
+	//   instead return `FailedPrecondition` with a `ReferenceUpdate` structured error.
 	UserDeleteBranch(ctx context.Context, in *UserDeleteBranchRequest, opts ...grpc.CallOption) (*UserDeleteBranchResponse, error)
 	// UserCreateTag creates a new tag.
 	UserCreateTag(ctx context.Context, in *UserCreateTagRequest, opts ...grpc.CallOption) (*UserCreateTagResponse, error)
@@ -338,9 +343,14 @@ type OperationServiceServer interface {
 	//
 	// - Returns `InvalidArgument` in case either the branch name or user are not set.
 	// - Returns `FailedPrecondition` in case the branch does not exist.
-	// - Returns `OK` with a `PreReceiveError` in case custom hooks refused the update.
-	// - Returns `FailedPrecondition` in case updating the reference fails because of a concurrent
-	//   write to the same reference.
+	// - Returns `OK` with a `PreReceiveError` in case custom hooks refused the update. If the
+	//   `gitaly_user_delete_branch_structured_errors` feature flag is enabled this error case will
+	//   instead return `PermissionDenied` with either a `CustomHook` or AccessCheck` structured
+	//   error.
+	// - Returns `FailedPrecondition` in case updating the reference fails because
+	//   of a concurrent write to the same reference. If the
+	//   `gitaly_user_delete_branch_structured_errors` feature flag is set this error case will
+	//   instead return `FailedPrecondition` with a `ReferenceUpdate` structured error.
 	UserDeleteBranch(context.Context, *UserDeleteBranchRequest) (*UserDeleteBranchResponse, error)
 	// UserCreateTag creates a new tag.
 	UserCreateTag(context.Context, *UserCreateTagRequest) (*UserCreateTagResponse, error)
diff --git a/proto/operations.proto b/proto/operations.proto
index 5ecf78553..927dc67a8 100644
--- a/proto/operations.proto
+++ b/proto/operations.proto
@@ -35,9 +35,14 @@ service OperationService {
   //
   // - Returns `InvalidArgument` in case either the branch name or user are not set.
   // - Returns `FailedPrecondition` in case the branch does not exist.
-  // - Returns `OK` with a `PreReceiveError` in case custom hooks refused the update.
-  // - Returns `FailedPrecondition` in case updating the reference fails because of a concurrent
-  //   write to the same reference.
+  // - Returns `OK` with a `PreReceiveError` in case custom hooks refused the update. If the
+  //   `gitaly_user_delete_branch_structured_errors` feature flag is enabled this error case will
+  //   instead return `PermissionDenied` with either a `CustomHook` or AccessCheck` structured
+  //   error.
+  // - Returns `FailedPrecondition` in case updating the reference fails because
+  //   of a concurrent write to the same reference. If the
+  //   `gitaly_user_delete_branch_structured_errors` feature flag is set this error case will
+  //   instead return `FailedPrecondition` with a `ReferenceUpdate` structured error.
   rpc UserDeleteBranch(UserDeleteBranchRequest) returns (UserDeleteBranchResponse) {
     option (op_type) = {
       op: MUTATOR