Fix invalid op sequence when partially replacing filters with index s…

…cans

src/execution_plan/optimizations/utilize_indices.c

@@ -497,15 +497,15 @@ void reduce_scan_op(ExecutionPlan *plan, NodeByLabelScan *scan) {
 		RSResultsIterator *iter = RediSearch_GetResultsIterator(root, rs_idx);
 		// Build the Index Scan.
 		OpBase *indexOp = NewIndexScanOp(scan->op.plan, scan->g, scan->n, rs_idx, iter);
-		/* In place, replace the last redundant filter (highest in the op tree) with the new scan op.
-		 * This ensures that the children array of the scan's parent op does not get shuffled,
-		 * avoiding problems with stream-sensitive ops like SemiApply. */
+		/* Remove the redundant filter op without reordering its parent op's child array
+		 * (avoiding problems with stream-sensitive ops like SemiApply). */
 		OpBase *last_filter = (OpBase *)array_pop(filters);
 		filters_count--;
-		ExecutionPlan_ReplaceOp(plan, last_filter, indexOp);
-		// Free the redundant filter and scan op.
+		ExecutionPlan_RemoveOp(plan, last_filter);
 		OpBase_Free(last_filter);
-		ExecutionPlan_RemoveOp(plan, (OpBase *)scan);
+
+		/* Replace the redundant scan op with the newly-constructed Index Scan. */
+		ExecutionPlan_ReplaceOp(plan, (OpBase *)scan, indexOp);
 		OpBase_Free((OpBase *)scan);
 	}
 

tests/flow/test_index_scans.py

@@ -234,3 +234,15 @@ def test07_index_scan_and_id(self):
         self.env.assertEqual(2, len(query_result.result_set))
         expected_result = [[nodes[7]], [nodes[8]]]
         self.env.assertEquals(expected_result, query_result.result_set)
+
+    # Validate placement of index scans and filter ops when not all filters can be replaced.
+    def test08_index_scan_multiple_filters(self):
+        query = "MATCH (p:person) WHERE p.age = 30 AND NOT EXISTS(p.fakeprop) RETURN p.name"
+        plan = redis_graph.execution_plan(query)
+        self.env.assertIn('Index Scan', plan)
+        self.env.assertNotIn('Label Scan', plan)
+        self.env.assertIn('Filter', plan)
+
+        query_result = redis_graph.query(query)
+        expected_result = ["Lucy Yanfital"]
+        self.env.assertEquals(query_result.result_set[0], expected_result)