// error-pattern: requires `generator` lang_item
-#![feature(no_core, lang_items, unboxed_closures)]
+#![feature(no_core, lang_items, unboxed_closures, tuple_trait)]
#![no_core]
#[lang = "sized"] pub trait Sized { }
+#[lang = "tuple_trait"] pub trait Tuple { }
+
#[lang = "fn_once"]
#[rustc_paren_sugar]
-pub trait FnOnce<Args> {
+pub trait FnOnce<Args: Tuple> {
type Output;
extern "rust-call" fn call_once(self, args: Args) -> Self::Output;