Change SeqScan node to contain Scan node

This makes the structure of all Scan-derived nodes the same,
independent of whether they have additional fields.

Discussion: https://www.postgresql.org/message-id/flat/c1097590-a6a4-486a-64b1-e1f9cc0533ce@enterprisedb.com

src/backend/executor/nodeSeqscan.c

@@ -151,7 +151,7 @@ ExecInitSeqScan(SeqScan *node, EState *estate, int eflags)
 	 */
 	scanstate->ss.ss_currentRelation =
 		ExecOpenScanRelation(estate,
-							 node->scanrelid,
+							 node->scan.scanrelid,
 							 eflags);
 
 	/* and create slot with the appropriate rowtype */
@@ -169,7 +169,7 @@ ExecInitSeqScan(SeqScan *node, EState *estate, int eflags)
 	 * initialize child expressions
 	 */
 	scanstate->ss.ps.qual =
-		ExecInitQual(node->plan.qual, (PlanState *) scanstate);
+		ExecInitQual(node->scan.plan.qual, (PlanState *) scanstate);
 
 	return scanstate;
 }

src/backend/nodes/readfuncs.c

@@ -1833,7 +1833,7 @@ _readSeqScan(void)
 {
 	READ_LOCALS_NO_FIELDS(SeqScan);
 
-	ReadCommonScan(local_node);
+	ReadCommonScan(&local_node->scan);
 
 	READ_DONE();
 }

src/backend/optimizer/plan/createplan.c

@@ -2855,7 +2855,7 @@ create_seqscan_plan(PlannerInfo *root, Path *best_path,
 							 scan_clauses,
 							 scan_relid);
 
-	copy_generic_path_info(&scan_plan->plan, best_path);
+	copy_generic_path_info(&scan_plan->scan.plan, best_path);
 
 	return scan_plan;
 }
@@ -5369,13 +5369,13 @@ make_seqscan(List *qptlist,
 			 Index scanrelid)
 {
 	SeqScan    *node = makeNode(SeqScan);
-	Plan	   *plan = &node->plan;
+	Plan	   *plan = &node->scan.plan;
 
 	plan->targetlist = qptlist;
 	plan->qual = qpqual;
 	plan->lefttree = NULL;
 	plan->righttree = NULL;
-	node->scanrelid = scanrelid;
+	node->scan.scanrelid = scanrelid;
 
 	return node;
 }

src/backend/optimizer/plan/setrefs.c

@@ -516,12 +516,12 @@ set_plan_refs(PlannerInfo *root, Plan *plan, int rtoffset)
 			{
 				SeqScan    *splan = (SeqScan *) plan;
 
-				splan->scanrelid += rtoffset;
-				splan->plan.targetlist =
-					fix_scan_list(root, splan->plan.targetlist,
+				splan->scan.scanrelid += rtoffset;
+				splan->scan.plan.targetlist =
+					fix_scan_list(root, splan->scan.plan.targetlist,
 								  rtoffset, NUM_EXEC_TLIST(plan));
-				splan->plan.qual =
-					fix_scan_list(root, splan->plan.qual,
+				splan->scan.plan.qual =
+					fix_scan_list(root, splan->scan.plan.qual,
 								  rtoffset, NUM_EXEC_QUAL(plan));
 			}
 			break;

src/include/nodes/plannodes.h

@@ -348,7 +348,10 @@ typedef struct Scan
  *		sequential scan node
  * ----------------
  */
-typedef Scan SeqScan;
+typedef struct SeqScan
+{
+	Scan		scan;
+} SeqScan;
 
 /* ----------------
  *		table sample scan node