avoid cycles when creating fake candidates

node/malus/src/variants/common.rs

@@ -162,11 +162,20 @@ where
 pub fn create_fake_candidate_commitments(
 	persisted_validation_data: &PersistedValidationData,
 ) -> CandidateCommitments {
+	// Backing rejects candidates which output the same head as the parent,
+	// therefore we must create a new head which is not equal to the parent.
+	let mut head_data = persisted_validation_data.parent_head.clone();
+	if head_data.0.is_empty() {
+		head_data.0.push(0);
+	} else {
+		head_data.0[0] = head_data.0[0].wrapping_add(1);
+	};
+
 	CandidateCommitments {
 		upward_messages: Default::default(),
 		horizontal_messages: Default::default(),
 		new_validation_code: None,
-		head_data: persisted_validation_data.parent_head.clone(),
+		head_data,
 		processed_downward_messages: 0,
 		hrmp_watermark: persisted_validation_data.relay_parent_number,
 	}