MDEV-16708: Unsupported commands for prepared statements

Follow-up patch for the bug MDEV-25197 that fixes missed restoring
of thd->cur_stmt on returning error code.

Developed by Dmitry Shulga.

This fixes up the merge d2e2d329
and closes MDEV-25413.

mysql-test/main/ps.result

@@ -5568,4 +5568,38 @@ ERROR 42S02: Table 'test.x' doesn't exist
 DEALLOCATE PREPARE stmt;
 DROP VIEW v1;
 DROP TABLE t1;
-# MDEV-25413 FIXME: enable the MDEV-25197 test
+#
+# MDEV-25197: The statement set password=password('') executed in PS mode
+#             fails in case it is run by a user with expired password
+#
+CREATE USER user1@localhost PASSWORD EXPIRE;
+SET @disconnect_on_expired_password_save=@@global.disconnect_on_expired_password;
+SET GLOBAL disconnect_on_expired_password=OFF;
+connect con1,localhost,user1;
+connection con1;
+# Check that no regular statement like SELECT can be prepared
+# by a user with an expired password
+PREPARE stmt FROM "SELECT 1";
+ERROR HY000: You must SET PASSWORD before executing this statement
+# Check that the DEALLOCATE PREPARE statement can be run by a user
+# with an expired password
+PREPARE stmt FROM "SET password=password('')";
+DEALLOCATE PREPARE stmt;
+# Check that the SET PASSWORD statement can be executed in PS mode by
+# a user with an expired password
+PREPARE stmt FROM "SET password=password('')";
+EXECUTE stmt;
+PREPARE stmt FROM "SELECT 1";
+# Check that user's password is not expired anymore
+EXECUTE stmt;
+1
+1
+DEALLOCATE PREPARE stmt;
+# Clean up
+disconnect con1;
+connection default;
+SET GLOBAL disconnect_on_expired_password=@disconnect_on_expired_password_save;
+DROP USER user1@localhost;
+#
+# End of 10.4 tests
+#

mysql-test/main/ps.test

@@ -4999,9 +4999,6 @@ DEALLOCATE PREPARE stmt;
 DROP VIEW v1;
 DROP TABLE t1;
 
---echo # MDEV-25413 FIXME: enable the MDEV-25197 test
---exit
-
 --echo #
 --echo # MDEV-25197: The statement set password=password('') executed in PS mode
 --echo #             fails in case it is run by a user with expired password

sql/sql_prepare.cc

@@ -4257,6 +4257,7 @@ bool Prepared_statement::prepare(const char *packet, uint packet_len)
     thd->restore_backup_statement(this, &stmt_backup);
     thd->restore_active_arena(this, &stmt_backup);
     thd->stmt_arena= old_stmt_arena;
+    thd->cur_stmt = save_cur_stmt;
     my_error(ER_MUST_CHANGE_PASSWORD, MYF(0));
     DBUG_RETURN(true);
   }