Improve handling of CustomPath/CustomPlan(State) children.

Allow CustomPath to have a list of paths, CustomPlan a list of plans,
and CustomPlanState a list of planstates known to the core system, so
that custom path/plan providers can more reasonably use this
infrastructure for nodes with multiple children.

KaiGai Kohei, per a design suggestion from Tom Lane, with some
further kibitzing by me.

1 files changed, 21 insertions, 4 deletions

diff --git a/src/backend/optimizer/plan/subselect.c b/src/backend/optimizer/plan/subselect.c
index f80abb494c7..4708b87f330 100644
--- a/src/backend/optimizer/plan/subselect.c
+++ b/src/backend/optimizer/plan/subselect.c
@@ -2373,10 +2373,27 @@ finalize_plan(PlannerInfo *root, Plan *plan, Bitmapset *valid_params,
 			break;
 
 		case T_CustomScan:
-			finalize_primnode((Node *) ((CustomScan *) plan)->custom_exprs,
-							  &context);
-			/* We assume custom_scan_tlist cannot contain Params */
-			context.paramids = bms_add_members(context.paramids, scan_params);
+			{
+				CustomScan *cscan = (CustomScan *) plan;
+				ListCell   *lc;
+
+				finalize_primnode((Node *) cscan->custom_exprs,
+								  &context);
+				/* We assume custom_scan_tlist cannot contain Params */
+				context.paramids =
+					bms_add_members(context.paramids, scan_params);
+
+				/* child nodes if any */
+				foreach (lc, cscan->custom_plans)
+				{
+					context.paramids =
+						bms_add_members(context.paramids,
+										finalize_plan(root,
+													  (Plan *) lfirst(lc),
+													  valid_params,
+													  scan_params));
+				}
+			}
 			break;
 
 		case T_ModifyTable: