Bug#20146455: FIND_KEY_CI RETURNS NULL, CAUSES CRASH IN FILL_ALTER_INPLACE_INFO

The problem was that the server could terminate if a generated
foreign key index was renamed by the same ALTER TABLE statement
that added a new foreign key with the same name.

The reason this happened is the server figured out that the
two foreign keys would result in two generated keys so similar
that one of them was redundant. If the redundant key was the
same key that was renamed, the code which handles index renames
in fill_alter_inplace_info() could not find the key to rename.

This patch fixes the problem by treating a renamed key as if
it is no longer generated.

Author: jhauglid

mysql-test/r/alter_table.result

@@ -3382,3 +3382,33 @@ info: Records: 0  Duplicates: 0  Warnings: 0
 ALTER TABLE t1 ALGORITHM=INPLACE, DROP INDEX fld1,
 ADD FULLTEXT INDEX fld1(fld1);
 DROP TABLE t1;
+#
+# Bug#20146455: FIND_KEY_CI RETURNS NULL, CAUSES CRASH IN
+#               FILL_ALTER_INPLACE_INFO
+#
+CREATE TABLE t1 (a INT PRIMARY KEY, b INT,
+FOREIGN KEY (b) REFERENCES t1(a)) ENGINE= MyISAM;
+ALTER TABLE t1 RENAME INDEX b TO w, ADD FOREIGN KEY (b) REFERENCES t1(a);
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) NOT NULL,
+  `b` int(11) DEFAULT NULL,
+  PRIMARY KEY (`a`),
+  KEY `w` (`b`)
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP TABLE t1;
+CREATE TABLE t1 (a INT PRIMARY KEY, b INT,
+FOREIGN KEY (b) REFERENCES t1(a)) ENGINE= InnoDB;
+ALTER TABLE t1 RENAME INDEX b TO w, ADD FOREIGN KEY (b) REFERENCES t1(a);
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) NOT NULL,
+  `b` int(11) DEFAULT NULL,
+  PRIMARY KEY (`a`),
+  KEY `w` (`b`),
+  CONSTRAINT `t1_ibfk_1` FOREIGN KEY (`b`) REFERENCES `t1` (`a`),
+  CONSTRAINT `t1_ibfk_2` FOREIGN KEY (`b`) REFERENCES `t1` (`a`)
+) ENGINE=InnoDB DEFAULT CHARSET=latin1
+DROP TABLE t1;

mysql-test/t/alter_table.test

@@ -2684,3 +2684,21 @@ ALTER TABLE t1 DROP INDEX fld1, ADD FULLTEXT INDEX fld1(fld1);
 ALTER TABLE t1 ALGORITHM=INPLACE, DROP INDEX fld1,
 ADD FULLTEXT INDEX fld1(fld1);
 DROP TABLE t1;
+
+
+--echo #
+--echo # Bug#20146455: FIND_KEY_CI RETURNS NULL, CAUSES CRASH IN
+--echo #               FILL_ALTER_INPLACE_INFO
+--echo #
+
+CREATE TABLE t1 (a INT PRIMARY KEY, b INT,
+                 FOREIGN KEY (b) REFERENCES t1(a)) ENGINE= MyISAM;
+ALTER TABLE t1 RENAME INDEX b TO w, ADD FOREIGN KEY (b) REFERENCES t1(a);
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+CREATE TABLE t1 (a INT PRIMARY KEY, b INT,
+                 FOREIGN KEY (b) REFERENCES t1(a)) ENGINE= InnoDB;
+ALTER TABLE t1 RENAME INDEX b TO w, ADD FOREIGN KEY (b) REFERENCES t1(a);
+SHOW CREATE TABLE t1;
+DROP TABLE t1;

sql/sql_table.cc

@@ -7888,6 +7888,13 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
 
           key_name= rename_key->new_name;
           rename_key_it.remove();
+          /*
+            If the user has explicitly renamed the key, we should no longer
+            treat it as generated. Otherwise this key might be automatically
+            dropped by mysql_prepare_create_table() and this will confuse
+            code in fill_alter_inplace_info().
+          */
+          key_info->flags &= ~HA_GENERATED_KEY;
           break;
         }
       }