MDEV-13205 InnoDB: Failing assertion: !dict_index_is_online_ddl(index) upon ALTER TABLE

dict_foreign_find_index(): Ignore incompletely created indexes. After a failed ADD UNIQUE INDEX, an incompletely created index could be left behind until the next ALTER TABLE statement.

Author: dr-m

mysql-test/suite/innodb/r/innodb-index-online.result

@@ -339,6 +339,22 @@ ERROR 42000: Duplicate key name 'c2h'
 SET DEBUG_SYNC = 'RESET';
 SET GLOBAL innodb_monitor_disable = module_ddl;
 DROP TABLE t1;
+#
+# MDEV-13205 assertion !dict_index_is_online_ddl(index) upon ALTER TABLE
+#
+CREATE TABLE t1 (c VARCHAR(64)) ENGINE=InnoDB;
+SET DEBUG_SYNC = 'row_log_apply_before SIGNAL t1u_created WAIT_FOR dup_done';
+ALTER TABLE t1 ADD UNIQUE(c);
+SET DEBUG_SYNC = 'now WAIT_FOR t1u_created';
+BEGIN;
+INSERT INTO t1 VALUES('bar'),('bar');
+SET DEBUG_SYNC = 'now SIGNAL dup_done';
+ERROR 23000: Duplicate entry 'bar' for key 'c'
+SET DEBUG_SYNC = 'RESET';
+CREATE TABLE t2 (c VARCHAR(64)) ENGINE=InnoDB;
+ALTER TABLE t2 ADD FOREIGN KEY (c) REFERENCES t1 (c);
+ERROR HY000: Can't create table `test`.`#sql-temporary` (errno: 150 "Foreign key constraint is incorrectly formed")
+DROP TABLE t2,t1;
 SET GLOBAL innodb_file_per_table = @global_innodb_file_per_table_orig;
 SET GLOBAL innodb_monitor_enable = default;
 SET GLOBAL innodb_monitor_disable = default;

mysql-test/suite/innodb/t/innodb-index-online.test

@@ -382,8 +382,6 @@ connection default;
 reap;
 --enable_parsing
 #remove below con1 disconnect if above test case is enabled
-connection con1;
-disconnect con1;
 connection default;
 
 SHOW CREATE TABLE t1;
@@ -399,6 +397,31 @@ SET GLOBAL innodb_monitor_disable = module_ddl;
 
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-13205 assertion !dict_index_is_online_ddl(index) upon ALTER TABLE
+--echo #
+CREATE TABLE t1 (c VARCHAR(64)) ENGINE=InnoDB;
+SET DEBUG_SYNC = 'row_log_apply_before SIGNAL t1u_created WAIT_FOR dup_done';
+send ALTER TABLE t1 ADD UNIQUE(c);
+
+connection con1;
+SET DEBUG_SYNC = 'now WAIT_FOR t1u_created';
+BEGIN;
+INSERT INTO t1 VALUES('bar'),('bar');
+SET DEBUG_SYNC = 'now SIGNAL dup_done';
+
+connection default;
+--error ER_DUP_ENTRY
+reap;
+
+SET DEBUG_SYNC = 'RESET';
+disconnect con1;
+CREATE TABLE t2 (c VARCHAR(64)) ENGINE=InnoDB;
+--replace_regex /#sql-[0-9a-f_]*/#sql-temporary/
+--error ER_CANT_CREATE_TABLE
+ALTER TABLE t2 ADD FOREIGN KEY (c) REFERENCES t1 (c);
+DROP TABLE t2,t1;
+
 # Check that all connections opened by test cases in this file are really
 # gone so execution of other tests won't be affected by their presence.
 --source include/wait_until_count_sessions.inc

storage/innobase/dict/dict0dict.cc

@@ -3364,6 +3364,7 @@ dict_foreign_find_index(
 if (types_idx != index
  && !(index->type & DICT_FTS)
  && !index->to_be_dropped
+ && !dict_index_is_online_ddl(index)
  && dict_foreign_qualify_index(
  table, col_names, columns, n_cols,
  index, types_idx,

storage/xtradb/dict/dict0dict.cc

@@ -3378,6 +3378,7 @@ dict_foreign_find_index(
 if (types_idx != index
  && !(index->type & DICT_FTS)
  && !index->to_be_dropped
+ && !dict_index_is_online_ddl(index)
  && dict_foreign_qualify_index(
  table, col_names, columns, n_cols,
  index, types_idx,