1 error[E0658]: parenthetical notation is only stable when used with `Fn`-family traits (see issue #29625)
2 --> $DIR/unboxed-closure-feature-gate.rs:23:16
4 LL | let x: Box<Foo(isize)>;
7 = help: add #![feature(unboxed_closures)] to the crate attributes to enable
9 error: aborting due to previous error
11 For more information about this error, try `rustc --explain E0658`.