MDEV-25460: Assertion `!is_set() || (m_status == DA_OK_BULK && is_bulk_op())'

failed in Diagnostics_area::set_ok_status in my_ok from
mysql_sql_stmt_prepare

Analysis: Before PREPARE is executed, binlog_format is STATEMENT.
This PREPARE had SET STATEMENT which sets binlog_format to ROW. Now after
PREPARE is done we reset the binlog_format (back to STATEMENT). But we have
temporary table, it doesn't let changing binlog_format=ROW to
binlog_format=STATEMENT and gives error which goes unreported. This
unreported error eventually causes assertion failure.
Fix: Change return type for LEX::restore_set_statement_var() to bool and
make it return error state.

mysql-test/extra/binlog_tests/mysqlbinlog_row_engine.inc

@@ -1921,3 +1921,28 @@ let $MYSQLD_DATADIR= `select @@datadir`;
 DROP TABLE t1;
 
 
+--echo #
+--echo # Beginning of 10.2 test
+--echo #
+--echo # MDEV-25460: Assertion `!is_set() || (m_status == DA_OK_BULK &&
+--echo # is_bulk_op())' failed in Diagnostics_area::set_ok_status in my_ok
+--echo # from mysql_sql_stmt_prepare
+--echo #
+
+CREATE TEMPORARY TABLE a (c INT) ENGINE=InnoDB;
+CREATE TABLE b (c INT) ENGINE=InnoDB;
+
+--error ER_TEMP_TABLE_PREVENTS_SWITCH_OUT_OF_RBR
+PREPARE s FROM 'SET STATEMENT binlog_format=ROW FOR SELECT * FROM b';
+
+DROP TABLE b;
+DROP TEMPORARY TABLE a;
+
+CREATE TEMPORARY TABLE t (c INT);
+--error ER_TEMP_TABLE_PREVENTS_SWITCH_OUT_OF_RBR
+PREPARE s FROM 'SET STATEMENT binlog_format=ROW FOR SELECT 1';
+DROP TEMPORARY TABLE t;
+
+--echo #
+--echo # End of 10.2 test
+--echo #

mysql-test/suite/binlog/r/binlog_mysqlbinlog_row_innodb.result

@@ -6352,3 +6352,23 @@ ROLLBACK /* added by mysqlbinlog */;
 # Cleanup.
 #
 DROP TABLE t1;
+#
+# Beginning of 10.2 test
+#
+# MDEV-25460: Assertion `!is_set() || (m_status == DA_OK_BULK &&
+# is_bulk_op())' failed in Diagnostics_area::set_ok_status in my_ok
+# from mysql_sql_stmt_prepare
+#
+CREATE TEMPORARY TABLE a (c INT) ENGINE=InnoDB;
+CREATE TABLE b (c INT) ENGINE=InnoDB;
+PREPARE s FROM 'SET STATEMENT binlog_format=ROW FOR SELECT * FROM b';
+ERROR HY000: Cannot switch out of the row-based binary log format when the session has open temporary tables
+DROP TABLE b;
+DROP TEMPORARY TABLE a;
+CREATE TEMPORARY TABLE t (c INT);
+PREPARE s FROM 'SET STATEMENT binlog_format=ROW FOR SELECT 1';
+ERROR HY000: Cannot switch out of the row-based binary log format when the session has open temporary tables
+DROP TEMPORARY TABLE t;
+#
+# End of 10.2 test
+#

mysql-test/suite/binlog/r/binlog_mysqlbinlog_row_myisam.result

@@ -6393,3 +6393,29 @@ ROLLBACK /* added by mysqlbinlog */;
 # Cleanup.
 #
 DROP TABLE t1;
+#
+# Beginning of 10.2 test
+#
+# MDEV-25460: Assertion `!is_set() || (m_status == DA_OK_BULK &&
+# is_bulk_op())' failed in Diagnostics_area::set_ok_status in my_ok
+# from mysql_sql_stmt_prepare
+#
+CREATE TEMPORARY TABLE a (c INT) ENGINE=InnoDB;
+Warnings:
+Warning	1286	Unknown storage engine 'InnoDB'
+Warning	1266	Using storage engine MyISAM for table 'a'
+CREATE TABLE b (c INT) ENGINE=InnoDB;
+Warnings:
+Warning	1286	Unknown storage engine 'InnoDB'
+Warning	1266	Using storage engine MyISAM for table 'b'
+PREPARE s FROM 'SET STATEMENT binlog_format=ROW FOR SELECT * FROM b';
+ERROR HY000: Cannot switch out of the row-based binary log format when the session has open temporary tables
+DROP TABLE b;
+DROP TEMPORARY TABLE a;
+CREATE TEMPORARY TABLE t (c INT);
+PREPARE s FROM 'SET STATEMENT binlog_format=ROW FOR SELECT 1';
+ERROR HY000: Cannot switch out of the row-based binary log format when the session has open temporary tables
+DROP TEMPORARY TABLE t;
+#
+# End of 10.2 test
+#

sql/sql_lex.cc

@@ -4766,18 +4766,19 @@ void LEX::free_arena_for_set_stmt()
   DBUG_VOID_RETURN;
 }
 
-void LEX::restore_set_statement_var()
+bool LEX::restore_set_statement_var()
 {
+  bool err= false;
   DBUG_ENTER("LEX::restore_set_statement_var");
   if (!old_var_list.is_empty())
   {
     DBUG_PRINT("info", ("vars: %d", old_var_list.elements));
-    sql_set_variables(thd, &old_var_list, false);
+    err= sql_set_variables(thd, &old_var_list, false);
     old_var_list.empty();
     free_arena_for_set_stmt();
   }
   DBUG_ASSERT(!is_arena_for_set_stmt());
-  DBUG_VOID_RETURN;
+  DBUG_RETURN(err);
 }
 
 /*

sql/sql_lex.h

@@ -3094,7 +3094,7 @@ struct LEX: public Query_tables_list
 
   int print_explain(select_result_sink *output, uint8 explain_flags,
                     bool is_analyze, bool *printed_anything);
-  void restore_set_statement_var();
+  bool restore_set_statement_var();
 
   void init_last_field(Column_definition *field, const char *name, CHARSET_INFO *cs);
   void set_last_field_type(const Lex_field_type_st &type);

sql/sql_prepare.cc

@@ -4283,7 +4283,7 @@ bool Prepared_statement::prepare(const char *packet, uint packet_len)
     Restore original values of variables modified on handling
     SET STATEMENT clause.
   */
-  thd->lex->restore_set_statement_var();
+  error|= thd->lex->restore_set_statement_var();
 
   /* The order is important */
   lex->unit.cleanup();