Fix cloning of row triggers to sub-partitions

When row triggers exist in partitioned partitions that are not either
part of FKs or deferred unique constraints, they are not correctly
cloned to their partitions.  That's because they are marked "internal",
and those are purposefully skipped when doing the clone triggers dance.
Fix by relaxing the condition on which internal triggers are skipped.

Amit Langote initially diagnosed the problem and proposed a fix, but I
used a different approach.

Reported-by: Petr Fedorov
Discussion: https://postgr.es/m/6b3f0646-ba8c-b3a9-c62d-1c6651a1920f@phystech.edu

src/backend/commands/tablecmds.c

@@ -15931,6 +15931,54 @@ out:
 	MemoryContextDelete(cxt);
 }
 
+/*
+ * isPartitionTrigger
+ *		Subroutine for CloneRowTriggersToPartition: determine whether
+ *		the given trigger has been cloned from another one.
+ *
+ * We use pg_depend as a proxy for this, since we don't have any direct
+ * evidence.  This is an ugly hack to cope with a catalog deficiency.
+ * Keep away from children.  Do not stare with naked eyes.  Do not propagate.
+ */
+static bool
+isPartitionTrigger(Oid trigger_oid)
+{
+	Relation	pg_depend;
+	ScanKeyData key[2];
+	SysScanDesc	scan;
+	HeapTuple	tup;
+	bool		found = false;
+
+	pg_depend = table_open(DependRelationId, AccessShareLock);
+
+	ScanKeyInit(&key[0], Anum_pg_depend_classid,
+				BTEqualStrategyNumber,
+				F_OIDEQ,
+				ObjectIdGetDatum(TriggerRelationId));
+	ScanKeyInit(&key[1], Anum_pg_depend_objid,
+				BTEqualStrategyNumber,
+				F_OIDEQ,
+				ObjectIdGetDatum(trigger_oid));
+
+	scan = systable_beginscan(pg_depend, DependDependerIndexId,
+							  true, NULL, 2, key);
+	while ((tup = systable_getnext(scan)) != NULL)
+	{
+		Form_pg_depend	dep = (Form_pg_depend) GETSTRUCT(tup);
+
+		if (dep->refclassid == TriggerRelationId)
+		{
+			found = true;
+			break;
+		}
+	}
+
+	systable_endscan(scan);
+	table_close(pg_depend, AccessShareLock);
+
+	return found;
+}
+
 /*
  * CloneRowTriggersToPartition
  *		subroutine for ATExecAttachPartition/DefineRelation to create row
@@ -15971,8 +16019,21 @@ CloneRowTriggersToPartition(Relation parent, Relation partition)
 		if (!TRIGGER_FOR_ROW(trigForm->tgtype))
 			continue;
 
-		/* We don't clone internal triggers, either */
-		if (trigForm->tgisinternal)
+		/*
+		 * Internal triggers require careful examination.  Ideally, we don't
+		 * clone them.
+		 *
+		 * However, if our parent is a partitioned relation, there might be
+		 * internal triggers that need cloning.  In that case, we must
+		 * skip clone it if the trigger on parent depends on another trigger.
+		 *
+		 * Note we dare not verify that the other trigger belongs to an
+		 * ancestor relation of our parent, because that creates deadlock
+		 * opportunities.
+		 */
+		if (trigForm->tgisinternal &&
+			(!parent->rd_rel->relispartition ||
+			 !isPartitionTrigger(trigForm->oid)))
 			continue;
 
 		/*

src/test/regress/expected/triggers.out

@@ -1981,15 +1981,22 @@ create trigger trg1 after insert on trigpart for each row execute procedure trig
 create table trigpart2 partition of trigpart for values from (1000) to (2000);
 create table trigpart3 (like trigpart);
 alter table trigpart attach partition trigpart3 for values from (2000) to (3000);
+create table trigpart4 partition of trigpart for values from (3000) to (4000) partition by range (a);
+create table trigpart41 partition of trigpart4 for values from (3000) to (3500);
+create table trigpart42 (like trigpart);
+alter table trigpart4 attach partition trigpart42 for values from (3500) to (4000);
 select tgrelid::regclass, tgname, tgfoid::regproc from pg_trigger
   where tgrelid::regclass::text like 'trigpart%' order by tgrelid::regclass::text;
-  tgrelid  | tgname |     tgfoid      
------------+--------+-----------------
- trigpart  | trg1   | trigger_nothing
- trigpart1 | trg1   | trigger_nothing
- trigpart2 | trg1   | trigger_nothing
- trigpart3 | trg1   | trigger_nothing
-(4 rows)
+  tgrelid   | tgname |     tgfoid      
+------------+--------+-----------------
+ trigpart   | trg1   | trigger_nothing
+ trigpart1  | trg1   | trigger_nothing
+ trigpart2  | trg1   | trigger_nothing
+ trigpart3  | trg1   | trigger_nothing
+ trigpart4  | trg1   | trigger_nothing
+ trigpart41 | trg1   | trigger_nothing
+ trigpart42 | trg1   | trigger_nothing
+(7 rows)
 
 drop trigger trg1 on trigpart1;	-- fail
 ERROR:  cannot drop trigger trg1 on table trigpart1 because trigger trg1 on table trigpart requires it
@@ -2003,12 +2010,15 @@ HINT:  You can drop trigger trg1 on table trigpart instead.
 drop table trigpart2;			-- ok, trigger should be gone in that partition
 select tgrelid::regclass, tgname, tgfoid::regproc from pg_trigger
   where tgrelid::regclass::text like 'trigpart%' order by tgrelid::regclass::text;
-  tgrelid  | tgname |     tgfoid      
------------+--------+-----------------
- trigpart  | trg1   | trigger_nothing
- trigpart1 | trg1   | trigger_nothing
- trigpart3 | trg1   | trigger_nothing
-(3 rows)
+  tgrelid   | tgname |     tgfoid      
+------------+--------+-----------------
+ trigpart   | trg1   | trigger_nothing
+ trigpart1  | trg1   | trigger_nothing
+ trigpart3  | trg1   | trigger_nothing
+ trigpart4  | trg1   | trigger_nothing
+ trigpart41 | trg1   | trigger_nothing
+ trigpart42 | trg1   | trigger_nothing
+(6 rows)
 
 drop trigger trg1 on trigpart;		-- ok, all gone
 select tgrelid::regclass, tgname, tgfoid::regproc from pg_trigger

src/test/regress/sql/triggers.sql

@@ -1366,6 +1366,10 @@ create trigger trg1 after insert on trigpart for each row execute procedure trig
 create table trigpart2 partition of trigpart for values from (1000) to (2000);
 create table trigpart3 (like trigpart);
 alter table trigpart attach partition trigpart3 for values from (2000) to (3000);
+create table trigpart4 partition of trigpart for values from (3000) to (4000) partition by range (a);
+create table trigpart41 partition of trigpart4 for values from (3000) to (3500);
+create table trigpart42 (like trigpart);
+alter table trigpart4 attach partition trigpart42 for values from (3500) to (4000);
 select tgrelid::regclass, tgname, tgfoid::regproc from pg_trigger
   where tgrelid::regclass::text like 'trigpart%' order by tgrelid::regclass::text;
 drop trigger trg1 on trigpart1;	-- fail