Fix for bug #11314 (HAVING DEFAULT() hangs)

mysql-test/t/func_default.test:
  test result fixed
sql/item.cc:
  code simplified using real_item() method,
  error returning added

mysql-test/t/func_default.test

@@ -16,4 +16,13 @@ explain select * from t1 where str <> default(str);
 #show create table from t1;
 #insert into t2 select select default(str), default(strnull), default(intg), default(rel) from t1;
 
-drop table t1;
\ No newline at end of file
+drop table t1;
+
+#
+# Bug #11314 (HAVING DEFAULT() hangs)
+#
+CREATE TABLE t1 (s varchar(20), id int(11));
+INSERT INTO t1 VALUES (1, 'one'), (2, 'two'), (3, 'three');
+SELECT s, 32 AS mi FROM t1 GROUP BY s HAVING DEFAULT(mi) IS NULL;
+DROP TABLE t1;
+

sql/item.cc

@@ -4454,16 +4454,14 @@ bool Item_default_value::fix_fields(THD *thd,
   }
   if (!arg->fixed && arg->fix_fields(thd, table_list, &arg))
     return TRUE;
-  
-  if (arg->type() == REF_ITEM)
+
+  arg= arg->real_item();
+  if (arg->type() != FIELD_ITEM)
   {
-    Item_ref *ref= (Item_ref *)arg;
-    if (ref->ref[0]->type() != FIELD_ITEM)
-    {
-      return TRUE;
-    }
-    arg= ref->ref[0];
+    my_error(ER_NO_DEFAULT_FOR_FIELD, MYF(0), arg->name);
+    return TRUE;
   }
+
   field_arg= (Item_field *)arg;
   if (field_arg->field->flags & NO_DEFAULT_VALUE_FLAG)
   {