Fix the case where trigger returns null to skip the row.

Per report #41.

expected/plv8.out

@@ -521,6 +521,64 @@ SELECT * FROM test_tbl;
  4 | s4
 (3 rows)
 
+-- One more trigger
+CREATE FUNCTION test_trigger2() RETURNS trigger AS
+$$
+	var tuple;
+	switch (TG_OP) {
+	case "INSERT":
+		tuple = NEW;
+		break;
+	case "UPDATE":
+		tuple = OLD;
+		break;
+	case "DELETE":
+		tuple = OLD;
+		break;
+	default:
+		return;
+	}
+	if (tuple.subject == "skip") {
+		return null;
+	}
+	if (tuple.subject == "modify" && NEW) {
+		NEW.val = tuple.val * 2;
+		return NEW;
+	}
+$$
+LANGUAGE "plv8";
+CREATE TABLE trig_table (subject text, val int);
+INSERT INTO trig_table VALUES('skip', 1);
+CREATE TRIGGER test_trigger2
+  BEFORE INSERT OR UPDATE OR DELETE
+  ON trig_table FOR EACH ROW
+  EXECUTE PROCEDURE test_trigger2();
+INSERT INTO trig_table VALUES
+  ('skip', 1), ('modify', 2), ('noop', 3);
+SELECT * FROM trig_table;
+ subject | val 
+---------+-----
+ skip    |   1
+ modify  |   4
+ noop    |   3
+(3 rows)
+
+UPDATE trig_table SET val = 10;
+SELECT * FROM trig_table;
+ subject | val 
+---------+-----
+ skip    |   1
+ modify  |   8
+ noop    |  10
+(3 rows)
+
+DELETE FROM trig_table;
+SELECT * FROM trig_table;
+ subject | val 
+---------+-----
+ skip    |   1
+(1 row)
+
 -- ERRORS
 CREATE FUNCTION syntax_error() RETURNS text AS '@' LANGUAGE plv8;
 ERROR:  SyntaxError: Unexpected token ILLEGAL

plv8.cc

@@ -615,8 +615,16 @@ CallTrigger(PG_FUNCTION_ARGS, plv8_exec_env *xenv)
 	if (newtup.IsEmpty())
 		throw js_error(try_catch);
 
-	if (TRIGGER_FIRED_BY_UPDATE(event) &&
-			!(newtup->IsUndefined() || newtup->IsNull()))
+	/*
+	 * If the function specifically returned null, return NULL to
+	 * tell executor to skip the operation.  Otherwise, the function
+	 * result is the tuple to be returned.
+	 */
+	if (newtup->IsNull() || !TRIGGER_FIRED_FOR_ROW(event))
+	{
+		result = PointerGetDatum(NULL);
+	}
+	else if (!newtup->IsUndefined())
 	{
 		TupleDesc		tupdesc = RelationGetDescr(rel);
 		Converter		conv(tupdesc);

sql/plv8.sql

@@ -295,6 +295,48 @@ UPDATE test_tbl SET i = 101, s = 'DEF' WHERE i = 1;
 DELETE FROM test_tbl WHERE i >= 100;
 SELECT * FROM test_tbl;
 
+-- One more trigger
+CREATE FUNCTION test_trigger2() RETURNS trigger AS
+$$
+	var tuple;
+	switch (TG_OP) {
+	case "INSERT":
+		tuple = NEW;
+		break;
+	case "UPDATE":
+		tuple = OLD;
+		break;
+	case "DELETE":
+		tuple = OLD;
+		break;
+	default:
+		return;
+	}
+	if (tuple.subject == "skip") {
+		return null;
+	}
+	if (tuple.subject == "modify" && NEW) {
+		NEW.val = tuple.val * 2;
+		return NEW;
+	}
+$$
+LANGUAGE "plv8";
+
+CREATE TABLE trig_table (subject text, val int);
+INSERT INTO trig_table VALUES('skip', 1);
+CREATE TRIGGER test_trigger2
+  BEFORE INSERT OR UPDATE OR DELETE
+  ON trig_table FOR EACH ROW
+  EXECUTE PROCEDURE test_trigger2();
+
+INSERT INTO trig_table VALUES
+  ('skip', 1), ('modify', 2), ('noop', 3);
+SELECT * FROM trig_table;
+UPDATE trig_table SET val = 10;
+SELECT * FROM trig_table;
+DELETE FROM trig_table;
+SELECT * FROM trig_table;
+
 -- ERRORS
 CREATE FUNCTION syntax_error() RETURNS text AS '@' LANGUAGE plv8;