MDEV-38620: Server crashes in setup_returning_fields upon 2nd execution

of multi-table-styled DELETE from a view

Analysis:
The item_list of builtin_select stores the fields that are there in the
RETURNING clause.
During the "EXECUTE" command, a "dummy item" is added into the item_list
of the select_lex(builtin_select) representing DELETE during
Sql_cmd_delete::precheck(). This snippet that adds a dummy item is added
because columnstore needs for temporary table. Results are put into a
temporary table and to create a temporary table we need to know what
columns are there which we get from the select_lex->item_list.
As a result, the item_list now has an item even when there is not really
RETURNING clause, resulting in execution of the setup_returning_fields()
when it should have exited already.

Fix:
Instead of checking whether builint_select's item_list is empty to
determine whether there is RETURNING clause, use a flag.

Author: mariadb-RuchaDeodhar

mysql-test/main/ps.result

@@ -6138,4 +6138,15 @@ a	?	?
 1	700	900
 DEALLOCATE PREPARE stmt;
 DROP TABLE t1;
+#
+# MDEV-38620: Server crashes in setup_returning_fields upon 2nd
+# execution of multi-table-styled DELETE from a view
+#
+CREATE TABLE t (a INT);
+CREATE VIEW v AS SELECT * FROM t;
+PREPARE stmt FROM "DELETE v FROM v";
+EXECUTE stmt;
+EXECUTE stmt;
+DROP VIEW v;
+DROP TABLE t;
 # End of 11.4 tests

mysql-test/main/ps.test

@@ -5592,4 +5592,18 @@ EXECUTE stmt USING 700, 900;
 DEALLOCATE PREPARE stmt;
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-38620: Server crashes in setup_returning_fields upon 2nd
+--echo # execution of multi-table-styled DELETE from a view
+--echo #
+
+CREATE TABLE t (a INT);
+CREATE VIEW v AS SELECT * FROM t;
+PREPARE stmt FROM "DELETE v FROM v";
+EXECUTE stmt;
+EXECUTE stmt;
+ 
+DROP VIEW v;
+DROP TABLE t;
+
 --echo # End of 11.4 tests

sql/sql_lex.cc

@@ -1337,6 +1337,8 @@ void LEX::start(THD *thd_arg)
 
   table_count_update= 0;
 
+  has_returning_list= false;
+
   memset(&trg_chistics, 0, sizeof(trg_chistics));
   DBUG_VOID_RETURN;
 }

sql/sql_lex.h

@@ -3667,6 +3667,9 @@ struct LEX: public Query_tables_list
     Activates enforcement of the LIMIT ROWS EXAMINED clause, if present
     in the query.
   */
+
+  bool has_returning_list;
+
   void set_limit_rows_examined()
   {
     if (limit_rows_examined)
@@ -4946,7 +4949,7 @@ struct LEX: public Query_tables_list
   SELECT_LEX *returning()
   { return &builtin_select; }
   bool has_returning()
-  { return !builtin_select.item_list.is_empty(); }
+  { return has_returning_list; }
 
 private:
   bool stmt_create_routine_start(const DDL_options_st &options)

sql/sql_yacc.yy

@@ -13730,6 +13730,7 @@ opt_returning:
 
             thd->lex->current_select->parsing_place= IN_RETURNING;
             thd->lex->push_context(&thd->lex->returning()->context);
+            thd->lex->has_returning_list= true;
           }
           select_item_list
           {