unboxed closure sugar not working in trait objects

[blaenk]

#17041 implemented unboxed closure sugar parsing for trait bounds, but it doesn't seem to be implemented for trait objects.

I realize that this example probably wouldn't work anyway due to the lack of higher-rank lifetimes, but the point is that the compiler yields a parser error.

playpen sample

trait Router {
  fn route(&mut self, p: &Path) -> Path;
}

impl<'a> Router for Box<FnMut(&'a Path) -> Path + 'a> {
  fn route(&mut self, p: &Path) -> Path {
    (*self).call_mut((p,))
  }
}

fn main() {}

@p1start observed this as well.

[ftxqxd]

FWIW, this applies to impls, too:

impl FnMut(int) -> int for Foo { ... }

fails to compile with a parser error.

[pnkfelix]

cc @aturon to close this once appropriate issue is constructed (we need a proper tracking / metabug for unboxed closures)

[aturon]

Not closing -- just removing nomination, as this is just a bug.

[nikomatsakis]

I am working in this as part of HRTB