Bug #12408412: GROUP_CONCAT + ORDER BY + INPUT/OUTPUT SAME

USER VARIABLE = CRASH

Moved the preparation of the variables that receive the output from 
SELECT INTO from execution time (JOIN:execute) to compile time 
(JOIN::prepare). This ensures that if the same variable is used in the
SELECT part of SELECT INTO it will be properly marked as non-const
for this query.
Test case added.
Used proper fast iterator.

mysql-test/r/user_var.result

@@ -485,4 +485,10 @@ f1	f2
 1	4
 DROP TRIGGER trg1;
 DROP TABLE t1;
+#
+# Bug #12408412: GROUP_CONCAT + ORDER BY + INPUT/OUTPUT
+#   SAME USER VARIABLE = CRASH
+#
+SET @bug12408412=1;
+SELECT GROUP_CONCAT(@bug12408412 ORDER BY 1) INTO @bug12408412;
 End of 5.5 tests

mysql-test/t/user_var.test

@@ -404,4 +404,13 @@ SELECT f1, f2 FROM t1 ORDER BY f2;
 DROP TRIGGER trg1;
 DROP TABLE t1;
 
+
+--echo #
+--echo # Bug #12408412: GROUP_CONCAT + ORDER BY + INPUT/OUTPUT
+--echo #   SAME USER VARIABLE = CRASH
+--echo #
+
+SET @bug12408412=1;
+SELECT GROUP_CONCAT(@bug12408412 ORDER BY 1) INTO @bug12408412;
+
 --echo End of 5.5 tests

sql/sql_class.cc

@@ -2855,13 +2855,42 @@ bool select_exists_subselect::send_data(List<Item> &items)
 int select_dumpvar::prepare(List<Item> &list, SELECT_LEX_UNIT *u)
 {
   unit= u;
+  List_iterator_fast<my_var> var_li(var_list);
+  List_iterator_fast<Item> it(list);
+  Item *item;
+  my_var *mv;
+  Item_func_set_user_var **suv;
   
   if (var_list.elements != list.elements)
   {
     my_message(ER_WRONG_NUMBER_OF_COLUMNS_IN_SELECT,
                ER(ER_WRONG_NUMBER_OF_COLUMNS_IN_SELECT), MYF(0));
     return 1;
-  }               
+  }
+
+  /*
+    Iterate over the destination variables and mark them as being
+    updated in this query.
+    We need to do this at JOIN::prepare time to ensure proper
+    const detection of Item_func_get_user_var that is determined
+    by the presence of Item_func_set_user_vars
+  */
+
+  suv= set_var_items= (Item_func_set_user_var **) 
+    sql_alloc(sizeof(Item_func_set_user_var *) * list.elements);
+
+  while ((mv= var_li++) && (item= it++))
+  {
+    if (!mv->local)
+    {
+      *suv= new Item_func_set_user_var(mv->s, item);
+      (*suv)->fix_fields(thd, 0);
+    }
+    else
+      *suv= NULL;
+    suv++;
+  }
+
   return 0;
 }
 
@@ -3178,6 +3207,7 @@ bool select_dumpvar::send_data(List<Item> &items)
   List_iterator<Item> it(items);
   Item *item;
   my_var *mv;
+  Item_func_set_user_var **suv;
   DBUG_ENTER("select_dumpvar::send_data");
 
   if (unit->offset_limit_cnt)
@@ -3190,20 +3220,19 @@ bool select_dumpvar::send_data(List<Item> &items)
     my_message(ER_TOO_MANY_ROWS, ER(ER_TOO_MANY_ROWS), MYF(0));
     DBUG_RETURN(1);
   }
-  while ((mv= var_li++) && (item= it++))
+  for (suv= set_var_items; ((mv= var_li++) && (item= it++)); suv++)
   {
     if (mv->local)
     {
+      DBUG_ASSERT(!*suv);
       if (thd->spcont->set_variable(thd, mv->offset, &item))
 	    DBUG_RETURN(1);
     }
     else
     {
-      Item_func_set_user_var *suv= new Item_func_set_user_var(mv->s, item);
-      if (suv->fix_fields(thd, 0))
-        DBUG_RETURN (1);
-      suv->save_item_result(item);
-      if (suv->update())
+      DBUG_ASSERT(*suv);
+      (*suv)->save_item_result(item);
+      if ((*suv)->update())
         DBUG_RETURN (1);
     }
   }

sql/sql_class.h

@@ -3531,6 +3531,7 @@ public:
 
 class select_dumpvar :public select_result_interceptor {
   ha_rows row_count;
+  Item_func_set_user_var **set_var_items;
 public:
   List<my_var> var_list;
   select_dumpvar()  { var_list.empty(); row_count= 0;}