Ensure that INSERT ... SELECT into a table with OIDs never copies row OIDs

from the source table.  This could never happen anyway before 8.4 because
the executor invariably applied a "junk filter" to rows due to be inserted;
but now that we skip doing that when it's not necessary, the case can occur.
Problem noted 2008-11-27 by KaiGai Kohei, though I misunderstood what he
was on about at the time (the opacity of the patch he proposed didn't help).

src/backend/executor/execMain.c

@@ -26,7 +26,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.322 2009/02/02 19:31:39 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.323 2009/02/08 18:02:27 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1766,6 +1766,21 @@ ExecInsert(TupleTableSlot *slot,
 	resultRelInfo = estate->es_result_relation_info;
 	resultRelationDesc = resultRelInfo->ri_RelationDesc;
 
+	/*
+	 * If the result relation has OIDs, force the tuple's OID to zero so that
+	 * heap_insert will assign a fresh OID.  Usually the OID already will be
+	 * zero at this point, but there are corner cases where the plan tree can
+	 * return a tuple extracted literally from some table with the same
+	 * rowtype.
+	 *
+	 * XXX if we ever wanted to allow users to assign their own OIDs to new
+	 * rows, this'd be the place to do it.  For the moment, we make a point
+	 * of doing this before calling triggers, so that a user-supplied trigger
+	 * could hack the OID if desired.
+	 */
+	if (resultRelationDesc->rd_rel->relhasoids)
+		HeapTupleSetOid(tuple, InvalidOid);
+
 	/* BEFORE ROW INSERT Triggers */
 	if (resultRelInfo->ri_TrigDesc &&
 		resultRelInfo->ri_TrigDesc->n_before_row[TRIGGER_EVENT_INSERT] > 0)
@@ -3033,6 +3048,12 @@ intorel_receive(TupleTableSlot *slot, DestReceiver *self)
 	 */
 	tuple = ExecMaterializeSlot(slot);
 
+	/*
+	 * force assignment of new OID (see comments in ExecInsert)
+	 */
+	if (myState->rel->rd_rel->relhasoids)
+		HeapTupleSetOid(tuple, InvalidOid);
+
 	heap_insert(myState->rel,
 				tuple,
 				myState->estate->es_output_cid,