MDEV-5309 - RENAME TABLE does not check for existence of the table's engine

When RENAME TABLE is executed, it apparently does not check whether the engine
is available (unlike ALTER TABLE .. RENAME, which does). It means that if the
engine in question was not loaded on some reason, the table might become
unusable, since the engine won't know about the change.

With this patch RENAME TABLE fails if storage engine is not available.

2 files changed, 4 insertions, 9 deletions

diff --git a/sql/sql_rename.cc b/sql/sql_rename.cc
index 2c17898f07c..6496e1895fb 100644
--- a/sql/sql_rename.cc
+++ b/sql/sql_rename.cc
@@ -238,7 +238,6 @@ do_rename(THD *thd, TABLE_LIST *ren_table, char *new_db, char *new_table_name,
 {
   int rc= 1;
   handlerton *hton;
-  bool new_exists, old_exists;
   const char *new_alias, *old_alias;
   DBUG_ENTER("do_rename");
 
@@ -254,17 +253,13 @@ do_rename(THD *thd, TABLE_LIST *ren_table, char *new_db, char *new_table_name,
   }
   DBUG_ASSERT(new_alias);
 
-  new_exists= ha_table_exists(thd, new_db, new_alias);
-
-  if (new_exists)
+  if (ha_table_exists(thd, new_db, new_alias))
   {
     my_error(ER_TABLE_EXISTS_ERROR, MYF(0), new_alias);
     DBUG_RETURN(1);                     // This can't be skipped
   }
 
-  old_exists= ha_table_exists(thd, ren_table->db, old_alias, &hton);
-
-  if (old_exists)
+  if (ha_table_exists(thd, ren_table->db, old_alias, &hton) && hton)
   {
     DBUG_ASSERT(!thd->locked_tables_mode);
     tdc_remove_table(thd, TDC_RT_REMOVE_ALL,
diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index 6ee0e9bc871..c31a6fd6474 100644
--- a/sql/sql_table.cc
+++ b/sql/sql_table.cc
@@ -5149,6 +5149,7 @@ mysql_rename_table(handlerton *base, const char *old_db,
   ulonglong save_bits= thd->variables.option_bits;
   int length;
   DBUG_ENTER("mysql_rename_table");
+  DBUG_ASSERT(base);
   DBUG_PRINT("enter", ("old: '%s'.'%s'  new: '%s'.'%s'",
                        old_db, old_name, new_db, new_name));
 
@@ -5156,8 +5157,7 @@ mysql_rename_table(handlerton *base, const char *old_db,
   if (flags & NO_FK_CHECKS) 
     thd->variables.option_bits|= OPTION_NO_FOREIGN_KEY_CHECKS;
 
-  file= (base == NULL ? 0 :
-         get_new_handler((TABLE_SHARE*) 0, thd->mem_root, base));
+  file= get_new_handler((TABLE_SHARE*) 0, thd->mem_root, base);
 
   build_table_filename(from, sizeof(from) - 1, old_db, old_name, "",
                        flags & FN_FROM_IS_TMP);