Boxed closures without explicit type info produces unhelpful error messages

[Munksgaard]

����The following piece of code works fine:

#![feature(default_type_params)]

use std::thunk::Invoke;

fn foo(x: Box<for <'a>Invoke<&'a int, ()>+'static>) {
    x.invoke(&42)
}

fn main() {
    foo(box move |: _: &int| () )
}

However, if you leave out the explicit type information in the creation of the boxed closure, like this:

#![feature(default_type_params)]

use std::thunk::Invoke;

fn foo(x: Box<for <'a>Invoke<&'a int, ()>+'static>) {
    x.invoke(&42)
}

fn main() {
    foo(box move |: _| () )
}

you get this rather unhelpful error message:

$ rustc foo.rs
foo.rs:10:9: 10:28 error: type mismatch: the type `closure[foo.rs:10:18: 10:28]` implements the trait `core::ops::FnOn
ce(_)`, but the trait `for<'a> core::ops::FnOnce(&'a int)` is required (expected concrete lifetime, found bound lifeti
me parameter 'a)                                                                                                     
foo.rs:10     foo(box move |: _| () )
                  ^~~~~~~~~~~~~~~~~~~
foo.rs:10:9: 10:28 note: required for the cast to the object type `for<'a> std::thunk::Invoke<&'a int> + 'static`
foo.rs:10     foo(box move |: _| () )
                  ^~~~~~~~~~~~~~~~~~~
error: aborting due to previous error

Maybe it should say something along the lines of boxed closures require explicit type information, or be able to infer the type by itself.

[steveklabnik]

Traige: closures have changed, std::thunk is gone, and nobody has commented in over a year. @Munksgaard if you can still reproduce this, let me know, but I think it's a non-issue now, or at least, don't know how to reproduce it.