MDEV-31661: Assertion `thd->lex == sp_instr_lex' failed in LEX*...

MDEV-31661: Assertion `thd->lex == sp_instr_lex' failed in LEX* sp_lex_instr::parse_expr(THD*, sp_head*, LEX*)

This is the follow-up patch for the task MDEV-5816 that fixes assert failure
that happened after recompilation of a stored routine containing a cursor
on its second execution.

The reason of assertion hit is that a state of the SP instruction sp_instr_cpush
wasn't reset after its SQL statement re-compiled.

To fix the issue the virtual method sp_lex_instr::on_after_expr_parsing
is overridden in the derived class sp_instr_cpush. Implementation of this method
does resetting of the data member sp_instr_cpush::m_metadata_changed

Additionally, implementation of the method
 sp_instr_set_trigger_field::on_after_expr_parsing
has been slightly modified to set the data member
 sp_instr_set_trigger_field::value
just before successful return. This data member is used to check whether this
SP instruction is still valid or should be re-compiled.
Resetting this data member before an instance of the class Item_trigger_field
be successfully allocated theoretically could lead to clearing of instruction's
state despite the fact that memory allocation was failed.

mysql-test/main/sp_validation.result

@@ -1890,4 +1890,25 @@ SET @@debug_dbug=@orig_dbug;
 DROP TABLE t1;
 DROP TABLE t2;
 DROP VIEW v1;
+#
+# MDEV-31661: Assertion `thd->lex == sp_instr_lex' failed in LEX* sp_lex_instr::parse_expr(THD*, sp_head*, LEX*)
+#
+CREATE OR REPLACE PROCEDURE p1()
+BEGIN
+DECLARE c CURSOR FOR SELECT * FROM t1;
+OPEN c;
+CLOSE c;
+END;
+$
+CALL p1;
+ERROR 42S02: Table 'test.t1' doesn't exist
+CREATE TABLE t1 (id INT);
+CALL p1;
+# Second execution of the stored procedure p1() after the dependent
+# table t1 has been created resulted in assert failure for server built
+# with debug
+CALL p1;
+# Clean up
+DROP PROCEDURE p1;
+DROP TABLE t1;
 SET sql_mode = default;

mysql-test/main/sp_validation.test

@@ -2682,4 +2682,35 @@ SET @@debug_dbug=@orig_dbug;
 DROP TABLE t1;
 DROP TABLE t2;
 DROP VIEW v1;
+
+--echo #
+--echo # MDEV-31661: Assertion `thd->lex == sp_instr_lex' failed in LEX* sp_lex_instr::parse_expr(THD*, sp_head*, LEX*)
+--echo #
+
+--delimiter $
+
+CREATE OR REPLACE PROCEDURE p1()
+BEGIN
+  DECLARE c CURSOR FOR SELECT * FROM t1;
+  OPEN c;
+  CLOSE c;
+END;
+$
+
+--delimiter ;
+
+--error ER_NO_SUCH_TABLE
+CALL p1;
+CREATE TABLE t1 (id INT);
+
+CALL p1;
+--echo # Second execution of the stored procedure p1() after the dependent
+--echo # table t1 has been created resulted in assert failure for server built
+--echo # with debug
+CALL p1;
+
+--echo # Clean up
+DROP PROCEDURE p1;
+DROP TABLE t1;
+
 SET sql_mode = default;

sql/sp_instr.cc

@@ -1209,20 +1209,22 @@ bool sp_instr_set_trigger_field::on_after_expr_parsing(THD *thd)
 {
   DBUG_ASSERT(thd->lex->current_select->item_list.elements == 1);
 
-  value= thd->lex->current_select->item_list.head();
-  DBUG_ASSERT(value != nullptr);
+  Item *val= thd->lex->current_select->item_list.head();
+  DBUG_ASSERT(val != nullptr);
 
   trigger_field = new (thd->mem_root)
     Item_trigger_field(thd, thd->lex->current_context(),
                        Item_trigger_field::NEW_ROW,
                        m_trigger_field_name, UPDATE_ACL, false);
 
-  if (!value || !trigger_field)
+  if (!val || !trigger_field)
     return true;
 
   thd->spcont->m_sp->m_cur_instr_trig_field_items.link_in_list(
     trigger_field, &trigger_field->next_trg_field);
 
+  value= val;
+
   return false;
 }
 

sql/sp_instr.h

@@ -1238,6 +1238,12 @@ class sp_instr_cpush : public sp_lex_instr, public sp_cursor
     return m_cursor_stmt;
   }
 
+  bool on_after_expr_parsing(THD *) override
+  {
+    m_metadata_changed= false;
+    return false;
+  }
+
 private:
   uint m_cursor;                /**< Frame offset (for debugging) */
   /**