MDEV-24919 Crash with subselect formed by table value constructor and

           used in set function

If a subselect is formed by a table value constructor (TVC) then the
following transformation is applied at the prepare stage:
  VALUES (v1), ... (vn) => SELECT * FROM (VALUES (v1), ... (vn)) tvc_x.
The transformation is performed by the function wrap_tvc() that resets
THD::LEX::current select to the top level select of the result of the
transformation. After the call of wrap_tvc() in the function
Item_subselect::wrap_tvc_into_select() the field THD::LEX::current must be
reset to the same select as before the call. It was not done. As a result
if the subselect formed by a TVC was an argument of a set function then
an assertion was hit in the function Item_sum::check_sum_func().

Approved by Oleksandr Byelkin <sanja@mariadb.com>

mysql-test/main/table_value_constr.result

@@ -2881,4 +2881,10 @@ NULL
 deallocate prepare stmt;
 drop view v1;
 drop table t1,t2,t3;
+#
+# MDEV-24919: subselect formed by TVC and used in set function
+#
+select sum((values(1)));
+sum((values(1)))
+1
 End of 10.3 tests

mysql-test/main/table_value_constr.test

@@ -1516,4 +1516,10 @@ deallocate prepare stmt;
 drop view v1;
 drop table t1,t2,t3;
 
+--echo #
+--echo # MDEV-24919: subselect formed by TVC and used in set function
+--echo #
+
+select sum((values(1)));
+
 --echo End of 10.3 tests

sql/sql_tvc.cc

@@ -648,7 +648,7 @@ st_select_lex *wrap_tvc(THD *thd, st_select_lex *tvc_sl,
                         st_select_lex *parent_select)
 {
   LEX *lex= thd->lex;
-  select_result *save_result= thd->lex->result;
+  select_result *save_result= lex->result;
   uint8 save_derived_tables= lex->derived_tables;
   thd->lex->result= NULL;
 
@@ -729,13 +729,13 @@ st_select_lex *wrap_tvc(THD *thd, st_select_lex *tvc_sl,
 
   if (arena)
     thd->restore_active_arena(arena, &backup);
-  thd->lex->result= save_result;
+  lex->result= save_result;
   return wrapper_sl;
 
 err:
   if (arena)
     thd->restore_active_arena(arena, &backup);
-  thd->lex->result= save_result;
+  lex->result= save_result;
   lex->derived_tables= save_derived_tables;
   return 0;
 }
@@ -819,14 +819,9 @@ Item_subselect::wrap_tvc_into_select(THD *thd, st_select_lex *tvc_sl)
   {
     if (engine->engine_type() == subselect_engine::SINGLE_SELECT_ENGINE)
       ((subselect_single_select_engine *) engine)->change_select(wrapper_sl);
-    lex->current_select= wrapper_sl;
-    return wrapper_sl;
-  }
-  else
-  {
-    lex->current_select= parent_select;
-    return 0;
   }
+  lex->current_select= parent_select;
+  return wrapper_sl;
 }