commit e082eadab813a4fb63975b4a5c5c96a401e73af2
Author: zhongbei.yk <zhongbei.yk@alibaba-inc.com>
Date:   Wed Jun 28 15:50:18 2023 +0800

    BUG#110976 full-text index with parser rebuilt incorrect
    
    When the ngram parser is added to a full-text index without a parser
    using the inplace DDL algorithm in a separate DDL statement, the
    full-text index does not change. When the copy DDL algorithm is used or
    the rebuilt DDL statement is divided into two DDL statement, the problem
    can be solved.
    
    Reason:
    In a inplace DDL, has_index_def_changed function is responsible for
    judging whether the index is changed. When the index is changed, the
    index will be rebuilt. However, when the full-text index’s parser is
    changed, has_index_def_changed has no logic to sense that change.
    
    How to fix:
    When the full-text index’s parser is changed, the ful-text index should
    be to be rebuilt. Add this judgment logic to the has_index_def_changed
    function.

diff --git a/mysql-test/r/bug110976.result b/mysql-test/r/bug110976.result
new file mode 100644
index 00000000000..0ad9b6c880e
--- /dev/null
+++ b/mysql-test/r/bug110976.result
@@ -0,0 +1,56 @@
+INSTALL PLUGIN simple_parser SONAME 'mypluglib.so';
+#####################################################################
+# 1. Prepare a table with a full-text index with default parser.
+#####################################################################
+CREATE TABLE t (name varchar(256), FULLTEXT KEY ft_index (name)) ENGINE = InnoDB;
+# full-text index should have no ngram parser.
+SHOW CREATE TABLE t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `name` varchar(256) DEFAULT NULL,
+  FULLTEXT KEY `ft_index` (`name`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
+#################################################################################################
+# 2. Modify full-text index from default parser to ngram parser in a DDL statement by inplace DDL
+#################################################################################################
+ALTER TABLE t
+DROP INDEX ft_index ,
+ADD FULLTEXT INDEX ft_index (name) WITH PARSER ngram , algorithm = inplace;
+# full-text index should have ngram parser. 
+SHOW CREATE TABLE t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `name` varchar(256) DEFAULT NULL,
+  FULLTEXT KEY `ft_index` (`name`) /*!50100 WITH PARSER `ngram` */ 
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
+################################################################################################
+# 3. Modify full-text index from ngram parser to simple_parser in a DDL statement by inplace DDL
+################################################################################################
+ALTER TABLE t
+DROP INDEX ft_index ,
+ADD FULLTEXT INDEX ft_index (name) WITH PARSER simple_parser , algorithm = inplace;
+# full-text index should have simple_parser. 
+SHOW CREATE TABLE t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `name` varchar(256) DEFAULT NULL,
+  FULLTEXT KEY `ft_index` (`name`) /*!50100 WITH PARSER `simple_parser` */ 
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
+##################################################################################################
+# 4. Modify full-text index from simple_parser to default parser in a DDL statement by inplace DDL
+##################################################################################################
+ALTER TABLE t
+DROP INDEX ft_index ,
+ADD FULLTEXT INDEX ft_index (name), algorithm = inplace;
+# full-text index should have no ngram parser.
+SHOW CREATE TABLE t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `name` varchar(256) DEFAULT NULL,
+  FULLTEXT KEY `ft_index` (`name`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
+#############
+# 4. Cleanup
+#############
+DROP TABLE t;
+UNINSTALL PLUGIN simple_parser;
\ No newline at end of file
diff --git a/mysql-test/t/bug110976.test b/mysql-test/t/bug110976.test
new file mode 100644
index 00000000000..0404efe36b5
--- /dev/null
+++ b/mysql-test/t/bug110976.test
@@ -0,0 +1,45 @@
+INSTALL PLUGIN simple_parser SONAME 'mypluglib.so';
+ 
+--echo #####################################################################
+--echo # 1. Prepare a table with a full-text index with default parser.
+--echo #####################################################################
+CREATE TABLE t (name varchar(256), FULLTEXT KEY ft_index (name)) ENGINE = InnoDB;
+ 
+--echo # full-text index should have no ngram parser.
+SHOW CREATE TABLE t;
+ 
+--echo #################################################################################################
+--echo # 2. Modify full-text index from default parser to ngram parser in a DDL statement by inplace DDL
+--echo #################################################################################################
+ALTER TABLE t
+DROP INDEX ft_index ,
+ADD FULLTEXT INDEX ft_index (name) WITH PARSER ngram , algorithm = inplace;
+ 
+--echo # full-text index should have ngram parser. 
+SHOW CREATE TABLE t;
+ 
+--echo ################################################################################################
+--echo # 3. Modify full-text index from ngram parser to simple_parser in a DDL statement by inplace DDL
+--echo ################################################################################################
+ALTER TABLE t
+DROP INDEX ft_index ,
+ADD FULLTEXT INDEX ft_index (name) WITH PARSER simple_parser , algorithm = inplace;
+ 
+--echo # full-text index should have simple_parser. 
+SHOW CREATE TABLE t;
+ 
+--echo ##################################################################################################
+--echo # 4. Modify full-text index from simple_parser to default parser in a DDL statement by inplace DDL
+--echo ##################################################################################################
+ALTER TABLE t
+DROP INDEX ft_index ,
+ADD FULLTEXT INDEX ft_index (name), algorithm = inplace;
+ 
+--echo # full-text index should have no ngram parser.
+SHOW CREATE TABLE t;
+ 
+--echo #############
+--echo # 4. Cleanup
+--echo #############
+DROP TABLE t;
+UNINSTALL PLUGIN simple_parser;
\ No newline at end of file
diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index 8dea91e74cb..f51b2700c46 100644
--- a/sql/sql_table.cc
+++ b/sql/sql_table.cc
@@ -11843,6 +11843,18 @@ static bool has_index_def_changed(Alter_inplace_info *ha_alter_info,
     }
   }
 
+  /*
+    Check whether the fulltext parsers has been chagned. 
+    1. Key with parser converted to key with built-in parser.
+    2. key with built-in parser converted to key with parser.
+    3. Key with parser converted to key with another parser.
+  */
+  if ((table_key->parser != nullptr && new_key->parser_name.str == nullptr) ||
+      (table_key->parser == nullptr && new_key->parser_name.str != nullptr) ||
+      (table_key->parser != nullptr && new_key->parser_name.str != nullptr &&
+      strcmp(plugin_name(table_key->parser)->str, new_key->parser_name.str)))
+    return true;
+
   return false;
 }