MDEV-16311 Server crash when using a NAME_CONST() with a CURSOR

Problem:
The problem was most likely introduced by a fix for MDEV-11597
(commit 5f0c31f) which removed
the assignment "killed= KILL_BAD_DATA" from THD::raise_condition().

Before MDEV-11597, sp_head::execute() tested thd->killed after
looping through the SP instructions and exited with an error
if thd->killed is set. After MDEV-11597, sp_head::execute()
stopped to notice errors and set the OK status on top of the
error status, which crashed on assert.

Fix:
Making sp_cursor::fetch() return -1 if server_side_cursor->fetch(1)
left an error in the diagnostics area. This makes the statement
"err_status= i->execute(thd, &ip)" in sp_head::execute() set the
error code and correctly break the SP instruction loop and
return on error without setting the OK status.

mysql-test/r/sp.result

@@ -8365,3 +8365,20 @@ ERROR HY000: Window function is allowed only in SELECT list and ORDER BY clause
 CALL p1(SUM(1));
 ERROR HY000: Invalid use of group function
 DROP PROCEDURE p1;
+#
+# MDEV-16311 Server crash when using a NAME_CONST() with a CURSOR
+#
+SET sql_mode=STRICT_ALL_TABLES;
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (10);
+BEGIN NOT ATOMIC
+DECLARE a INT;
+DECLARE c CURSOR FOR SELECT NAME_CONST('x','y') FROM t1;
+OPEN c;
+FETCH c INTO a;
+CLOSE c;
+END;
+$$
+ERROR 22007: Incorrect integer value: 'y' for column 'a' at row 1
+DROP TABLE t1;
+SET sql_mode=DEFAULT;

mysql-test/t/sp.test

@@ -9879,3 +9879,25 @@ CALL p1(ROW_NUMBER() OVER ());
 --error ER_INVALID_GROUP_FUNC_USE
 CALL p1(SUM(1));
 DROP PROCEDURE p1;
+
+
+--echo #
+--echo # MDEV-16311 Server crash when using a NAME_CONST() with a CURSOR
+--echo #
+
+SET sql_mode=STRICT_ALL_TABLES;
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (10);
+DELIMITER $$;
+--error ER_TRUNCATED_WRONG_VALUE_FOR_FIELD
+BEGIN NOT ATOMIC
+  DECLARE a INT;
+  DECLARE c CURSOR FOR SELECT NAME_CONST('x','y') FROM t1;
+  OPEN c;
+  FETCH c INTO a;
+  CLOSE c;
+END;
+$$
+DELIMITER ;$$
+DROP TABLE t1;
+SET sql_mode=DEFAULT;

sql/sp_rcontext.cc

@@ -509,9 +509,15 @@ int sp_cursor::fetch(THD *thd, List<sp_variable> *vars)
 
   result.set_spvar_list(vars);
 
+  DBUG_ASSERT(!thd->is_error());
+
   /* Attempt to fetch one row */
   if (server_side_cursor->is_open())
+  {
     server_side_cursor->fetch(1);
+    if (thd->is_error())
+      return -1; // e.g. data type conversion failed
+  }
 
   /*
     If the cursor was pointing after the last row, the fetch will