Fixed that mysql_upgrade doesn't give errors about mariadb.sys

The reason for this fix was that when I tried to run mysql_upgrade
at home to update an old 10.5 installation, mysql_upgrade failed
with warnings about mariadb.sys user not existing.

If the server was started with --skip-grants, there would be no warnings
from mysql_upgrade, but in some cases running mysql_upgrade again could
produce new warnings.

The reason for the warnings was that any access of the mysql.user view
will produce a warning if the mariadb.sys user does not exists.

Fixed with the following changes:
- Disable warnings about mariadb.sys user not existing
- Don't overwrite old mariadb.sys entries in tables_priv and global_priv
- Ensure that tables_priv has an entry for mariadb.sys if the user exists.
  This fixes an issue that tables_priv would not be updated if there
  was a failure directly after global_priv was updated.

client/mysql_upgrade.c

@@ -1029,6 +1029,7 @@ static const char *expected_errors[]=
   "ERROR 1347", /* 'mysql.user' is not of type 'BASE TABLE' */
   "ERROR 1348", /* Column 'Show_db_priv' is not updatable */
   "ERROR 1356", /* definer of view lack rights (UPDATE) */
+  "ERROR 1449", /* definer ('mariadb.sys'@'localhost') of mysql.user does not exist */
   0
 };
 

scripts/mysql_system_tables.sql

@@ -35,17 +35,15 @@ set @had_db_table= @@warning_count != 0;
 
 CREATE TABLE IF NOT EXISTS global_priv (Host char(60) binary DEFAULT '', User char(80) binary DEFAULT '', Priv JSON NOT NULL DEFAULT '{}' CHECK(JSON_VALID(Priv)), PRIMARY KEY (Host,User)) engine=Aria transactional=1 CHARACTER SET utf8 COLLATE utf8_bin comment='Users and global privileges';
 
-set @had_sys_user= 0 <> (select count(*) from mysql.global_priv where Host="localhost" and User="mariadb.sys");
-
 set @exists_user_view= EXISTS (SELECT * FROM information_schema.VIEWS WHERE TABLE_CATALOG = 'def' and TABLE_SCHEMA = 'mysql' and TABLE_NAME='user');
 
 set @exists_user_view_by_root= EXISTS (SELECT * FROM information_schema.VIEWS WHERE TABLE_CATALOG = 'def' and TABLE_SCHEMA = 'mysql' and TABLE_NAME='user' and DEFINER = 'mariadb.sys@localhost');
 
-set @need_sys_user_creation= (NOT @had_sys_user) AND (( NOT @exists_user_view) OR @exists_user_view_by_root);
+set @need_sys_user_creation= (( NOT @exists_user_view) OR @exists_user_view_by_root);
 
 CREATE TEMPORARY TABLE tmp_user_sys LIKE global_priv;
 INSERT INTO tmp_user_sys (Host,User,Priv) VALUES ('localhost','mariadb.sys','{"access":0,"plugin":"mysql_native_password","authentication_string":"","account_locked":true,"password_last_changed":0}');
-INSERT INTO global_priv SELECT * FROM tmp_user_sys WHERE 0 <> @need_sys_user_creation;
+INSERT IGNORE INTO global_priv SELECT * FROM tmp_user_sys WHERE 0 <> @need_sys_user_creation;
 DROP TABLE tmp_user_sys;
 
 
@@ -117,7 +115,7 @@ CREATE TABLE IF NOT EXISTS tables_priv ( Host char(60) binary DEFAULT '' NOT NUL
 
 CREATE TEMPORARY TABLE tmp_user_sys LIKE tables_priv;
 INSERT INTO tmp_user_sys (Host,Db,User,Table_name,Grantor,Timestamp,Table_priv) VALUES ('localhost','mysql','mariadb.sys','global_priv','root@localhost','0','Select,Delete');
-INSERT INTO tables_priv SELECT * FROM tmp_user_sys WHERE 0 <> @need_sys_user_creation;
+INSERT IGNORE INTO tables_priv SELECT * FROM tmp_user_sys WHERE 0 <> @need_sys_user_creation;
 DROP TABLE tmp_user_sys;
 
 CREATE TABLE IF NOT EXISTS columns_priv ( Host char(60) binary DEFAULT '' NOT NULL, Db char(64) binary DEFAULT '' NOT NULL, User char(80) binary DEFAULT '' NOT NULL, Table_name char(64) binary DEFAULT '' NOT NULL, Column_name char(64) binary DEFAULT '' NOT NULL, Timestamp timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, Column_priv set('Select','Insert','Update','References') COLLATE utf8_general_ci DEFAULT '' NOT NULL, PRIMARY KEY (Host,Db,User,Table_name,Column_name) ) engine=Aria transactional=1 CHARACTER SET utf8 COLLATE utf8_bin   comment='Column privileges';