Fixed bug #27932: the function LOCATE returned NULL if any

of its arguments was evaluated to NULL, while the predicate
LOCATE(str,NULL) IS NULL erroneously was evaluated to FALSE.

This happened because the Item_func_locate::fix_length_and_dec
method by mistake set the value of the maybe_null flag for 
the function item to 0. In consequence of this the function 
was considered as the one that could not ever return NULL.

mysql-test/r/func_str.result

@@ -2061,4 +2061,80 @@ C
 2707236321
 DROP TABLE t1, t2;
 DROP VIEW v1;
+SELECT LOCATE('foo', NULL) FROM DUAL;
+LOCATE('foo', NULL)
+NULL
+SELECT LOCATE(NULL, 'o') FROM DUAL;
+LOCATE(NULL, 'o')
+NULL
+SELECT LOCATE(NULL, NULL) FROM DUAL;
+LOCATE(NULL, NULL)
+NULL
+SELECT LOCATE('foo', NULL) IS NULL FROM DUAL;
+LOCATE('foo', NULL) IS NULL
+1
+SELECT LOCATE(NULL, 'o') IS NULL FROM DUAL;
+LOCATE(NULL, 'o') IS NULL
+1
+SELECT LOCATE(NULL, NULL) IS NULL FROM DUAL;
+LOCATE(NULL, NULL) IS NULL
+1
+SELECT ISNULL(LOCATE('foo', NULL)) FROM DUAL;
+ISNULL(LOCATE('foo', NULL))
+1
+SELECT ISNULL(LOCATE(NULL, 'o')) FROM DUAL;
+ISNULL(LOCATE(NULL, 'o'))
+1
+SELECT ISNULL(LOCATE(NULL, NULL)) FROM DUAL;
+ISNULL(LOCATE(NULL, NULL))
+1
+SELECT LOCATE('foo', NULL) <=> NULL FROM DUAL;
+LOCATE('foo', NULL) <=> NULL
+1
+SELECT LOCATE(NULL, 'o') <=> NULL FROM DUAL;
+LOCATE(NULL, 'o') <=> NULL
+1
+SELECT LOCATE(NULL, NULL) <=> NULL FROM DUAL;
+LOCATE(NULL, NULL) <=> NULL
+1
+CREATE TABLE t1 (id int NOT NULL PRIMARY KEY, a varchar(10), p varchar(10));
+INSERT INTO t1 VALUES (1, 'foo', 'o');
+INSERT INTO t1 VALUES (2, 'foo', NULL);
+INSERT INTO t1 VALUES (3, NULL, 'o');
+INSERT INTO t1 VALUES (4, NULL, NULL);
+SELECT id, LOCATE(a,p) FROM t1;
+id	LOCATE(a,p)
+1	0
+2	NULL
+3	NULL
+4	NULL
+SELECT id, LOCATE(a,p) IS NULL FROM t1;
+id	LOCATE(a,p) IS NULL
+1	0
+2	1
+3	1
+4	1
+SELECT id, ISNULL(LOCATE(a,p)) FROM t1;
+id	ISNULL(LOCATE(a,p))
+1	0
+2	1
+3	1
+4	1
+SELECT id, LOCATE(a,p) <=> NULL FROM t1;
+id	LOCATE(a,p) <=> NULL
+1	0
+2	1
+3	1
+4	1
+SELECT id FROM t1 WHERE LOCATE(a,p) IS NULL;
+id
+2
+3
+4
+SELECT id FROM t1 WHERE LOCATE(a,p) <=> NULL;
+id
+2
+3
+4
+DROP TABLE t1;
 End of 5.0 tests

mysql-test/t/func_str.test

@@ -1076,4 +1076,37 @@ SELECT * FROM (SELECT * FROM v1) x;
 DROP TABLE t1, t2;
 DROP VIEW v1;
 
+#
+# Bug #27932: LOCATE with argument evaluated to NULL
+#
+
+SELECT LOCATE('foo', NULL) FROM DUAL;
+SELECT LOCATE(NULL, 'o') FROM DUAL;
+SELECT LOCATE(NULL, NULL) FROM DUAL;
+SELECT LOCATE('foo', NULL) IS NULL FROM DUAL;
+SELECT LOCATE(NULL, 'o') IS NULL FROM DUAL;
+SELECT LOCATE(NULL, NULL) IS NULL FROM DUAL;
+SELECT ISNULL(LOCATE('foo', NULL)) FROM DUAL;
+SELECT ISNULL(LOCATE(NULL, 'o')) FROM DUAL;
+SELECT ISNULL(LOCATE(NULL, NULL)) FROM DUAL;
+SELECT LOCATE('foo', NULL) <=> NULL FROM DUAL;
+SELECT LOCATE(NULL, 'o') <=> NULL FROM DUAL;
+SELECT LOCATE(NULL, NULL) <=> NULL FROM DUAL;
+
+CREATE TABLE t1 (id int NOT NULL PRIMARY KEY, a varchar(10), p varchar(10));
+
+INSERT INTO t1 VALUES (1, 'foo', 'o');
+INSERT INTO t1 VALUES (2, 'foo', NULL);
+INSERT INTO t1 VALUES (3, NULL, 'o');
+INSERT INTO t1 VALUES (4, NULL, NULL);
+
+SELECT id, LOCATE(a,p) FROM t1;
+SELECT id, LOCATE(a,p) IS NULL FROM t1;
+SELECT id, ISNULL(LOCATE(a,p)) FROM t1;
+SELECT id, LOCATE(a,p) <=> NULL FROM t1;
+SELECT id FROM t1 WHERE LOCATE(a,p) IS NULL;
+SELECT id FROM t1 WHERE LOCATE(a,p) <=> NULL; 
+
+DROP TABLE t1;
+
 --echo End of 5.0 tests

sql/item_func.cc

@@ -2507,7 +2507,6 @@ longlong Item_func_coercibility::val_int()
 
 void Item_func_locate::fix_length_and_dec()
 {
-  maybe_null= 0;
   max_length= MY_INT32_NUM_DECIMAL_DIGITS;
   agg_arg_charsets(cmp_collation, args, 2, MY_COLL_CMP_CONV, 1);
 }