Fix trigger WHEN conditions when both BEFORE and AFTER triggers exist.

Due to tuple-slot mismanagement, evaluation of WHEN conditions for AFTER
ROW UPDATE triggers could crash if there had been a BEFORE ROW trigger
fired for the same update.  Fix by not trying to overload the use of
estate->es_trig_tuple_slot.  Per report from Yoran Heling.

Back-patch to 9.0, when trigger WHEN conditions were introduced.

src/backend/commands/trigger.c

@@ -2770,13 +2770,13 @@ TriggerEnabled(EState *estate, ResultRelInfo *relinfo,
 		}
 		if (HeapTupleIsValid(newtup))
 		{
-			if (estate->es_trig_tuple_slot == NULL)
+			if (estate->es_trig_newtup_slot == NULL)
 			{
 				oldContext = MemoryContextSwitchTo(estate->es_query_cxt);
-				estate->es_trig_tuple_slot = ExecInitExtraTupleSlot(estate);
+				estate->es_trig_newtup_slot = ExecInitExtraTupleSlot(estate);
 				MemoryContextSwitchTo(oldContext);
 			}
-			newslot = estate->es_trig_tuple_slot;
+			newslot = estate->es_trig_newtup_slot;
 			if (newslot->tts_tupleDescriptor != tupdesc)
 				ExecSetSlotDescriptor(newslot, tupdesc);
 			ExecStoreTuple(newtup, newslot, InvalidBuffer, false);

src/backend/executor/execMain.c

@@ -871,6 +871,7 @@ InitPlan(QueryDesc *queryDesc, int eflags)
 	estate->es_tupleTable = NIL;
 	estate->es_trig_tuple_slot = NULL;
 	estate->es_trig_oldtup_slot = NULL;
+	estate->es_trig_newtup_slot = NULL;
 
 	/* mark EvalPlanQual not active */
 	estate->es_epqTuple = NULL;

src/backend/executor/execUtils.c

@@ -124,6 +124,7 @@ CreateExecutorState(void)
 	estate->es_trig_target_relations = NIL;
 	estate->es_trig_tuple_slot = NULL;
 	estate->es_trig_oldtup_slot = NULL;
+	estate->es_trig_newtup_slot = NULL;
 
 	estate->es_param_list_info = NULL;
 	estate->es_param_exec_vals = NULL;

src/include/nodes/execnodes.h

@@ -354,7 +354,8 @@ typedef struct EState
 	/* Stuff used for firing triggers: */
 	List	   *es_trig_target_relations;		/* trigger-only ResultRelInfos */
 	TupleTableSlot *es_trig_tuple_slot; /* for trigger output tuples */
-	TupleTableSlot *es_trig_oldtup_slot;		/* for trigger old tuples */
+	TupleTableSlot *es_trig_oldtup_slot;		/* for TriggerEnabled */
+	TupleTableSlot *es_trig_newtup_slot;		/* for TriggerEnabled */
 
 	/* Parameter info: */
 	ParamListInfo es_param_list_info;	/* values of external params */

src/test/regress/expected/triggers.out

@@ -446,6 +446,35 @@ NOTICE:  trigger_func(after_upd_a_b_row) called: action = UPDATE, when = AFTER,
 NOTICE:  trigger_func(after_upd_b_row) called: action = UPDATE, when = AFTER, level = ROW
 NOTICE:  trigger_func(after_upd_b_stmt) called: action = UPDATE, when = AFTER, level = STATEMENT
 NOTICE:  trigger_func(after_upd_stmt) called: action = UPDATE, when = AFTER, level = STATEMENT
+--
+-- Test case for bug with BEFORE trigger followed by AFTER trigger with WHEN
+--
+CREATE TABLE some_t (some_col boolean NOT NULL);
+CREATE FUNCTION dummy_update_func() RETURNS trigger AS $$
+BEGIN
+  RAISE NOTICE 'dummy_update_func(%) called: action = %, old = %, new = %',
+    TG_ARGV[0], TG_OP, OLD, NEW;
+  RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+CREATE TRIGGER some_trig_before BEFORE UPDATE ON some_t FOR EACH ROW
+  EXECUTE PROCEDURE dummy_update_func('before');
+CREATE TRIGGER some_trig_aftera AFTER UPDATE ON some_t FOR EACH ROW
+  WHEN (NOT OLD.some_col AND NEW.some_col)
+  EXECUTE PROCEDURE dummy_update_func('aftera');
+CREATE TRIGGER some_trig_afterb AFTER UPDATE ON some_t FOR EACH ROW
+  WHEN (NOT NEW.some_col)
+  EXECUTE PROCEDURE dummy_update_func('afterb');
+INSERT INTO some_t VALUES (TRUE);
+UPDATE some_t SET some_col = TRUE;
+NOTICE:  dummy_update_func(before) called: action = UPDATE, old = (t), new = (t)
+UPDATE some_t SET some_col = FALSE;
+NOTICE:  dummy_update_func(before) called: action = UPDATE, old = (t), new = (f)
+NOTICE:  dummy_update_func(afterb) called: action = UPDATE, old = (t), new = (f)
+UPDATE some_t SET some_col = TRUE;
+NOTICE:  dummy_update_func(before) called: action = UPDATE, old = (f), new = (t)
+NOTICE:  dummy_update_func(aftera) called: action = UPDATE, old = (f), new = (t)
+DROP TABLE some_t;
 -- bogus cases
 CREATE TRIGGER error_upd_and_col BEFORE UPDATE OR UPDATE OF a ON main_table
 FOR EACH ROW EXECUTE PROCEDURE trigger_func('error_upd_and_col');

src/test/regress/sql/triggers.sql

@@ -308,6 +308,32 @@ SELECT pg_get_triggerdef(oid) FROM pg_trigger WHERE tgrelid = 'main_table'::regc
 UPDATE main_table SET a = 50;
 UPDATE main_table SET b = 10;
 
+--
+-- Test case for bug with BEFORE trigger followed by AFTER trigger with WHEN
+--
+
+CREATE TABLE some_t (some_col boolean NOT NULL);
+CREATE FUNCTION dummy_update_func() RETURNS trigger AS $$
+BEGIN
+  RAISE NOTICE 'dummy_update_func(%) called: action = %, old = %, new = %',
+    TG_ARGV[0], TG_OP, OLD, NEW;
+  RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+CREATE TRIGGER some_trig_before BEFORE UPDATE ON some_t FOR EACH ROW
+  EXECUTE PROCEDURE dummy_update_func('before');
+CREATE TRIGGER some_trig_aftera AFTER UPDATE ON some_t FOR EACH ROW
+  WHEN (NOT OLD.some_col AND NEW.some_col)
+  EXECUTE PROCEDURE dummy_update_func('aftera');
+CREATE TRIGGER some_trig_afterb AFTER UPDATE ON some_t FOR EACH ROW
+  WHEN (NOT NEW.some_col)
+  EXECUTE PROCEDURE dummy_update_func('afterb');
+INSERT INTO some_t VALUES (TRUE);
+UPDATE some_t SET some_col = TRUE;
+UPDATE some_t SET some_col = FALSE;
+UPDATE some_t SET some_col = TRUE;
+DROP TABLE some_t;
+
 -- bogus cases
 CREATE TRIGGER error_upd_and_col BEFORE UPDATE OR UPDATE OF a ON main_table
 FOR EACH ROW EXECUTE PROCEDURE trigger_func('error_upd_and_col');