MDEV-16130 wrong error message adding AS ROW START to versioned table

Author: midenok

mysql-test/suite/versioning/r/alter.result

@@ -80,13 +80,17 @@ t	CREATE TABLE `t` (
   `a` int(11) DEFAULT NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 alter table t add column trx_start timestamp(6) as row start;
-ERROR HY000: Table `t` is not system-versioned
+ERROR HY000: Duplicate ROW START column `trx_start`
 alter table t add system versioning;
 show create table t;
 Table	Create Table
 t	CREATE TABLE `t` (
   `a` int(11) DEFAULT NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1 WITH SYSTEM VERSIONING
+alter table t add column trx_start timestamp(6) as row start;
+ERROR HY000: Duplicate ROW START column `trx_start`
+alter table t modify a int as row start;
+ERROR HY000: Duplicate ROW START column `a`
 alter table t add column b int;
 show create table t;
 Table	Create Table
@@ -531,7 +535,7 @@ use test;
 # MDEV-15956 Strange ER_UNSUPPORTED_ACTION_ON_GENERATED_COLUMN upon ALTER on versioning column
 create or replace table t1 (i int, j int as (i), s timestamp(6) as row start, e timestamp(6) as row end, period for system_time(s,e)) with system versioning;
 alter table t1 modify s timestamp(6) as row start;
-ERROR HY000: Can not change system versioning field `s`
+ERROR HY000: Duplicate ROW START column `s`
 # ignore CHECK for historical rows
 create or replace table t (a int) with system versioning;
 insert into t values (0), (1);

mysql-test/suite/versioning/t/alter.test

@@ -68,12 +68,17 @@ select row_start from t;
 alter table t drop system versioning;
 show create table t;
 
---error ER_VERS_NOT_VERSIONED
+--error ER_VERS_DUPLICATE_ROW_START_END
 alter table t add column trx_start timestamp(6) as row start;
 
 alter table t add system versioning;
 show create table t;
 
+--error ER_VERS_DUPLICATE_ROW_START_END
+alter table t add column trx_start timestamp(6) as row start;
+--error ER_VERS_DUPLICATE_ROW_START_END
+alter table t modify a int as row start;
+
 alter table t add column b int;
 show create table t;
 
@@ -457,7 +462,7 @@ use test;
 
 --echo # MDEV-15956 Strange ER_UNSUPPORTED_ACTION_ON_GENERATED_COLUMN upon ALTER on versioning column
 create or replace table t1 (i int, j int as (i), s timestamp(6) as row start, e timestamp(6) as row end, period for system_time(s,e)) with system versioning;
---error ER_VERS_ALTER_SYSTEM_FIELD
+--error ER_VERS_DUPLICATE_ROW_START_END
 alter table t1 modify s timestamp(6) as row start;
 
 --echo # ignore CHECK for historical rows

sql/handler.cc

@@ -7301,13 +7301,15 @@ bool Vers_parse_info::fix_alter_info(THD *thd, Alter_info *alter_info,
     return false;
   }
 
+  if (!(alter_info->flags & ALTER_ADD_SYSTEM_VERSIONING))
   {
     List_iterator_fast<Create_field> it(alter_info->create_list);
     while (Create_field *f= it++)
     {
-      if (f->change.length && f->flags & VERS_SYSTEM_FIELD)
+      if (f->flags & VERS_SYSTEM_FIELD)
       {
-        my_error(ER_VERS_ALTER_SYSTEM_FIELD, MYF(0), f->field_name.str);
+        my_error(ER_VERS_DUPLICATE_ROW_START_END, MYF(0),
+                 f->flags & VERS_SYS_START_FLAG ? "START" : "END", f->field_name.str);
         return true;
       }
     }

sql/sql_table.cc

@@ -8159,12 +8159,6 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
         alter_ctx->datetime_field= def;
         alter_ctx->error_if_not_empty= TRUE;
     }
-    if (def->flags & VERS_SYSTEM_FIELD &&
-        !(alter_info->flags & ALTER_ADD_SYSTEM_VERSIONING))
-    {
-      my_error(ER_VERS_NOT_VERSIONED, MYF(0), table->s->table_name.str);
-      goto err;
-    }
     if (!def->after.str)
       new_create_list.push_back(def, thd->mem_root);
     else