Support TRUNCATE triggers on foreign tables.

Now some foreign data wrappers support TRUNCATE command.
So it's useful to support TRUNCATE triggers on foreign tables for
audit logging or for preventing undesired truncation.

Author: Yugo Nagata
Reviewed-by: Fujii Masao, Ian Lawrence Barwick
Discussion: https://postgr.es/m/20220630193848.5b02e0d6076b86617a915682@sraoss.co.jp

contrib/postgres_fdw/expected/postgres_fdw.out

@@ -6732,9 +6732,9 @@ BEGIN
 		TG_ARGV[0], TG_OP, TG_WHEN, TG_LEVEL;
 	RETURN NULL;
 END;$$;
-CREATE TRIGGER trig_stmt_before BEFORE DELETE OR INSERT OR UPDATE ON rem1
+CREATE TRIGGER trig_stmt_before BEFORE DELETE OR INSERT OR UPDATE OR TRUNCATE ON rem1
 	FOR EACH STATEMENT EXECUTE PROCEDURE trigger_func();
-CREATE TRIGGER trig_stmt_after AFTER DELETE OR INSERT OR UPDATE ON rem1
+CREATE TRIGGER trig_stmt_after AFTER DELETE OR INSERT OR UPDATE OR TRUNCATE ON rem1
 	FOR EACH STATEMENT EXECUTE PROCEDURE trigger_func();
 CREATE OR REPLACE FUNCTION trigger_data()  RETURNS trigger
 LANGUAGE plpgsql AS $$
@@ -6821,6 +6821,9 @@ NOTICE:  OLD: (1,update),NEW: (1,updateupdate)
 NOTICE:  trig_row_after(23, skidoo) AFTER ROW UPDATE ON rem1
 NOTICE:  OLD: (1,update),NEW: (1,updateupdate)
 NOTICE:  trigger_func(<NULL>) called: action = UPDATE, when = AFTER, level = STATEMENT
+truncate rem1;
+NOTICE:  trigger_func(<NULL>) called: action = TRUNCATE, when = BEFORE, level = STATEMENT
+NOTICE:  trigger_func(<NULL>) called: action = TRUNCATE, when = AFTER, level = STATEMENT
 -- cleanup
 DROP TRIGGER trig_row_before ON rem1;
 DROP TRIGGER trig_row_after ON rem1;
@@ -7087,7 +7090,7 @@ NOTICE:  trig_row_after(23, skidoo) AFTER ROW INSERT ON rem1
 NOTICE:  NEW: (13,"test triggered !")
   ctid  
 --------
- (0,32)
+ (0,25)
 (1 row)
 
 -- cleanup

contrib/postgres_fdw/sql/postgres_fdw.sql

@@ -1595,9 +1595,9 @@ BEGIN
 	RETURN NULL;
 END;$$;
 
-CREATE TRIGGER trig_stmt_before BEFORE DELETE OR INSERT OR UPDATE ON rem1
+CREATE TRIGGER trig_stmt_before BEFORE DELETE OR INSERT OR UPDATE OR TRUNCATE ON rem1
 	FOR EACH STATEMENT EXECUTE PROCEDURE trigger_func();
-CREATE TRIGGER trig_stmt_after AFTER DELETE OR INSERT OR UPDATE ON rem1
+CREATE TRIGGER trig_stmt_after AFTER DELETE OR INSERT OR UPDATE OR TRUNCATE ON rem1
 	FOR EACH STATEMENT EXECUTE PROCEDURE trigger_func();
 
 CREATE OR REPLACE FUNCTION trigger_data()  RETURNS trigger
@@ -1652,6 +1652,7 @@ delete from rem1;
 insert into rem1 values(1,'insert');
 update rem1 set f2  = 'update' where f1 = 1;
 update rem1 set f2 = f2 || f2;
+truncate rem1;
 
 
 -- cleanup

doc/src/sgml/ref/create_trigger.sgml

@@ -131,7 +131,7 @@ CREATE [ OR REPLACE ] [ CONSTRAINT ] TRIGGER <replaceable class="parameter">name
      <row>
       <entry align="center"><command>TRUNCATE</command></entry>
       <entry align="center">&mdash;</entry>
-      <entry align="center">Tables</entry>
+      <entry align="center">Tables and foreign tables</entry>
      </row>
      <row>
       <entry align="center" morerows="1"><literal>AFTER</literal></entry>
@@ -142,7 +142,7 @@ CREATE [ OR REPLACE ] [ CONSTRAINT ] TRIGGER <replaceable class="parameter">name
      <row>
       <entry align="center"><command>TRUNCATE</command></entry>
       <entry align="center">&mdash;</entry>
-      <entry align="center">Tables</entry>
+      <entry align="center">Tables and foreign tables</entry>
      </row>
      <row>
       <entry align="center" morerows="1"><literal>INSTEAD OF</literal></entry>

src/backend/commands/trigger.c

@@ -295,13 +295,6 @@ CreateTriggerFiringOn(CreateTrigStmt *stmt, const char *queryString,
 							RelationGetRelationName(rel)),
 					 errdetail("Foreign tables cannot have INSTEAD OF triggers.")));
 
-		if (TRIGGER_FOR_TRUNCATE(stmt->events))
-			ereport(ERROR,
-					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-					 errmsg("\"%s\" is a foreign table",
-							RelationGetRelationName(rel)),
-					 errdetail("Foreign tables cannot have TRUNCATE triggers.")));
-
 		/*
 		 * We disallow constraint triggers to protect the assumption that
 		 * triggers on FKs can't be deferred.  See notes with AfterTriggers