error[E0635]: unknown feature `tuple_trait` --> $DIR/lang-item-missing-generator.rs:2:51 | LL | #![feature(no_core, lang_items, unboxed_closures, tuple_trait)] | ^^^^^^^^^^^ error: requires `generator` lang_item --> $DIR/lang-item-missing-generator.rs:17:17 | LL | pub fn abc() -> impl FnOnce(f32) { | ^^^^^^^^^^^^^^^^ error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0635`.