dict_load_foreign(): Use a local variable instead of the 10-bit field

foreign->n_fields in order to preserve ON UPDATE CASCADE and
ON DELETE CASCADE flags.  For some reason, gcc does not warn about
shifting a 10-bit field to right by 24 bits.  (Bug #24741)

This bug was introduced while reducing the memory footprint of the
InnoDB data dictionary (Bug #20877).

innodb.test, innodb.result: Add a test case.

dict/dict0load.c

@@ -1110,6 +1110,7 @@ dict_load_foreign(
 	rec_t*		rec;
 	byte*		field;
 	ulint		len;
+	ulint		n_fields_and_type;
 	mtr_t		mtr;
 
 #ifdef UNIV_SYNC_DEBUG
@@ -1172,15 +1173,15 @@ dict_load_foreign(
 
 	foreign = dict_mem_foreign_create();
 
-	foreign->n_fields = mach_read_from_4(
+	n_fields_and_type = mach_read_from_4(
 		rec_get_nth_field_old(rec, 5, &len));
 
 	ut_a(len == 4);
 
-	/* We store the type to the bits 24-31 of n_fields */
+	/* We store the type in the bits 24..29 of n_fields_and_type. */
 
-	foreign->type = foreign->n_fields >> 24;
-	foreign->n_fields = foreign->n_fields & 0xFFFFFFUL;
+	foreign->type = n_fields_and_type >> 24;
+	foreign->n_fields = n_fields_and_type & 0x3FFUL;
 
 	foreign->id = mem_heap_strdup(foreign->heap, id);
 

mysql-test/innodb.result

@@ -3456,3 +3456,20 @@ OPTIMIZE TABLE t1;
 Table	Op	Msg_type	Msg_text
 test.t1	optimize	status	OK
 DROP TABLE t1;
+CREATE TABLE t1 (id int PRIMARY KEY, f int NOT NULL, INDEX(f)) ENGINE=InnoDB;
+CREATE TABLE t2 (id int PRIMARY KEY, f INT NOT NULL,
+CONSTRAINT t2_t1 FOREIGN KEY (id) REFERENCES t1 (id)
+ON DELETE CASCADE ON UPDATE CASCADE) ENGINE=InnoDB;
+ALTER TABLE t2 ADD FOREIGN KEY (f) REFERENCES t1 (f) ON
+DELETE CASCADE ON UPDATE CASCADE;
+SHOW CREATE TABLE t2;
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `id` int(11) NOT NULL,
+  `f` int(11) NOT NULL,
+  PRIMARY KEY (`id`),
+  KEY `f` (`f`),
+  CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`f`) REFERENCES `t1` (`f`) ON DELETE CASCADE ON UPDATE CASCADE,
+  CONSTRAINT `t2_t1` FOREIGN KEY (`id`) REFERENCES `t1` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
+) ENGINE=InnoDB DEFAULT CHARSET=latin1
+DROP TABLE t2, t1;

mysql-test/innodb.test

@@ -2503,6 +2503,22 @@ INSERT INTO t1 VALUES (1);
 OPTIMIZE TABLE t1;
 DROP TABLE t1;
 
+#
+# Bug #24741 (existing cascade clauses disappear when adding foreign keys)
+#
+
+CREATE TABLE t1 (id int PRIMARY KEY, f int NOT NULL, INDEX(f)) ENGINE=InnoDB;
+
+CREATE TABLE t2 (id int PRIMARY KEY, f INT NOT NULL,
+  CONSTRAINT t2_t1 FOREIGN KEY (id) REFERENCES t1 (id)
+  ON DELETE CASCADE ON UPDATE CASCADE) ENGINE=InnoDB;
+
+ALTER TABLE t2 ADD FOREIGN KEY (f) REFERENCES t1 (f) ON
+DELETE CASCADE ON UPDATE CASCADE;
+
+SHOW CREATE TABLE t2;
+DROP TABLE t2, t1;
+
 #######################################################################
 #                                                                     #
 # Please, DO NOT TOUCH this file as well as the innodb.result file.   #