workaround for IN's special treatment of first argument. Not for 4.1

mysql-test/r/range.result

@@ -253,4 +253,10 @@ explain select * from t1, t1 t2 where t1.y = 2 and t2.x >= 0 and t2.x <= t1.y;
 table	type	possible_keys	key	key_len	ref	rows	Extra
 t1	ref	y	y	5	const	1	Using where
 t2	range	x	x	5	NULL	2	Using where
+explain select count(*) from t1 where x in (1);
+table	type	possible_keys	key	key_len	ref	rows	Extra
+t1	range	x	x	5	NULL	1	Using where; Using index
+explain select count(*) from t1 where x in (1,2);
+table	type	possible_keys	key	key_len	ref	rows	Extra
+t1	range	x	x	5	NULL	2	Using where; Using index
 drop table t1;

mysql-test/t/range.test

@@ -198,5 +198,8 @@ explain select * from t1, t1 t2 where t1.y = 2 and t2.x >= t1.y-1 and t2.x <= t1
 # equation propagation
 explain select * from t1, t1 t2 where t1.y = 2 and t2.x between 0 and t1.y;
 explain select * from t1, t1 t2 where t1.y = 2 and t2.x >= 0 and t2.x <= t1.y;
+# testing IN
+explain select count(*) from t1 where x in (1);
+explain select count(*) from t1 where x in (1,2);
 drop table t1;
 

sql/sql_select.cc

@@ -1556,7 +1556,13 @@ add_key_fields(JOIN_TAB *stat,KEY_FIELD **key_fields,uint *and_level,
     if (cond_func->key_item()->type() == Item::FIELD_ITEM)
       add_key_field(key_fields,*and_level,
 		    ((Item_field*) (cond_func->key_item()))->field, 0,
+#ifndef TO_BE_REMOVED_IN_4_1
+                    /* special treatment for IN. Not necessary in 4.1 */
+                    cond_func->arguments()      + (cond_func->functype() != Item_func::IN_FUNC),
+                    cond_func->argument_count() - (cond_func->functype() != Item_func::IN_FUNC),
+#else
                     cond_func->arguments()+1, cond_func->argument_count()-1,
+#endif
                     usable_tables);
     break;
   case Item_func::OPTIMIZE_OP: