LabelScan with child reads data correctly after reset (RedisGraph#1086)

src/execution_plan/ops/op_node_by_label_scan.c

@@ -112,11 +112,12 @@ static Record NodeByLabelScanConsumeFromChild(OpBase *opBase) {
 	/* depleted will be true in the following cases:
 	 * 1. No iterator: GxB_MatrixTupleIter_next will fail and depleted will stay true. This scenario means
 	 * that there was no consumption of a record from a child, otherwise there was an iterator.
-	 * 2. Iterator depleted - For every child record the iterator finished the entire matrix scan and it needs to restart. */
-	while(depleted) {
+	 * 2. Iterator depleted - For every child record the iterator finished the entire matrix scan and it needs to restart.
+	 * The child record will be NULL if this is the op's first invocation or it has just been reset, in which case we
+	 * should also enter this loop. */
+	while(depleted || op->child_record == NULL) {
 		// Try to get a record.
 		if(op->child_record) OpBase_DeleteRecord(op->child_record);
-		op->child_record = NULL;
 		op->child_record = OpBase_Consume(op->op.children[0]);
 		if(op->child_record == NULL) return NULL;
 

tests/flow/test_path_filter.py

@@ -222,3 +222,28 @@ def test10_verify_apply_results(self):
         # Each source node should be returned exactly once.
         expected_results = [['a'], ['b']]
         self.env.assertEquals(result_set.result_set, expected_results)
+
+    def test11_unbound_path_filters(self):
+        # Build a graph with 2 nodes connected by 1 edge.
+        node0 = Node(node_id=0, label="L", properties={'x': 'a'})
+        node1 = Node(node_id=1, label="L", properties={'x': 'b'})
+        edge01 = Edge(src_node=node0, dest_node=node1, relation="R")
+        redis_graph.add_node(node0)
+        redis_graph.add_node(node1)
+        redis_graph.add_edge(edge01)
+        redis_graph.flush()
+
+        # Emit a query that uses an AntiSemiApply op to return values.
+        query = "MATCH (n:L) WHERE NOT (:L)-[]->() RETURN n.x ORDER BY n.x"
+        result_set = redis_graph.query(query)
+        # The WHERE filter evaluates to false, no results should be returned.
+        expected_result = []
+        self.env.assertEquals(result_set.result_set, expected_result)
+
+        # Emit a query that uses a SemiApply op to return values.
+        query = "MATCH (n:L) WHERE (:L)-[]->() RETURN n.x ORDER BY n.x"
+        result_set = redis_graph.query(query)
+        # The WHERE filter evaluates to true, all results should be returned.
+        expected_result = [['a'],
+                           ['b']]
+        self.env.assertEquals(result_set.result_set, expected_result)