HRTB and Associated Types combine to make fn not implement corresponding Fn trait

[gereeter]

trait LifetimeToType<'a> {
    type Out;
}

impl<'a> LifetimeToType<'a> for () {
    type Out = &'a ();
}

fn id<'a>(val: &'a ()) -> <() as LifetimeToType<'a>>::Out {
    val
}

fn assert_fn<F: for<'a> FnOnce(&'a ()) -> <() as LifetimeToType<'a>>::Out>(_func: F) { }

fn main() {
    assert_fn(id);
}

fails with

test.rs:16:5: 16:14 error: type mismatch resolving `for<'a> <fn(&'a ()) -> <() as LifetimeToType<'a>>::Out {id} as core::ops::FnOnce<(&'a (),)>>::Output == <() as LifetimeToType<'a>>::Out`:
 expected &-ptr,
    found associated type [E0271]
test.rs:16     assert_fn(id);
               ^~~~~~~~~
test.rs:16:5: 16:14 help: run `rustc --explain E0271` to see a detailed explanation
test.rs:16:5: 16:14 note: required by `assert_fn`
error: aborting due to previous error

[gereeter]

I'm using rustc 1.5.0-nightly (87cd2c082 2015-10-10).

[huonw]

cc @nikomatsakis

[jfager]

Still an issue (playpen).

[bstrie]

Triage: no change as of Rust 1.41:

error[E0271]: type mismatch resolving `for<'a> <for<'a> fn(&'a ()) -> <() as LifetimeToType<'a>>::Out {id} as std::ops::FnOnce<(&'a (),)>>::Output == <() as LifetimeToType<'a>>::Out`
  --> src/main.rs:16:5
   |
13 | fn assert_fn<F: for<'a> FnOnce(&'a ()) -> <() as LifetimeToType<'a>>::Out>(_func: F) { }
   |    ---------                              ------------------------------- required by this bound in `assert_fn`
...
16 |     assert_fn(id);
   |     ^^^^^^^^^ expected associated type, found `&()`
   |
   = note: expected associated type `<() as LifetimeToType<'_>>::Out`
                    found reference `&()`
   = note: consider constraining the associated type `<() as LifetimeToType<'_>>::Out` to `&()` or calling a method that returns `<() as LifetimeToType<'_>>::Out`
   = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html

[fmease]

Triage: This compiles just fine now.