rustdoc: Inlined associated types are missing bounds

[tomjakubowski]

e.g. compare http://doc.rust-lang.org/core/ops/trait.Deref.html and http://doc.rust-lang.org/std/ops/trait.Deref.html

[tomjakubowski]

N.B. There is an out of date FIXME(#18048) related to this

rust/src/librustdoc/clean/mod.rs

Lines 2384 to 2385 in 9f1ead8

	// FIXME(#18048): this is wrong, but cross-crate associated types are broken
	// anyway, for the time being.

(cc #18048)

[nrc]

Type params seem to be missing the un-bound ?Sized too. I assume this is the same bug, but not 100% sure. E.g., std::ops::Index vs core::ops::Index

[tomjakubowski]

Type params in general seem to be missing ?Sized, like in:

// foo.rs
pub fn f<T: ?Sized>(_: &T) { }

// bar.rs
extern crate foo;

pub use foo::f;

I'll make a new issue (#20924).

[SimonSapin]

Possibly the same bug, but impl documentation on re-exported types are also missing things for associated types:

http://doc.rust-lang.org/core/slice/struct.Iter.html#implementations

impl<'a, T> Index<Range<usize>> for Iter<'a, T>
  type Output = [T]
  fn index(&self, index: &Range<usize>) -> &[T]

http://doc.rust-lang.org/std/slice/struct.Iter.html#implementations

impl<'a, T> Index<Range<usize>> for Iter<'a, T>
  fn index(&self, index: &Range<usize>) -> &[T]
  type Output

[tomjakubowski]

OK, I'm pretty sure that defaults will have to wait until they're actually implemented for associated types, so I've changed the issue title.

[tomjakubowski]

Since my last PR landed you can actually see all the bounds on an inlined trait's associated types! Unfortunately it's very ugly (and : Sized appears while : ?Sized doesn't, contrary to a user's expectations).

http://doc.rust-lang.org/std/ops/trait.Add.html

pub trait Add<RHS = Self> where <Self as Add<RHS>>::Output: Sized {
    type Output;
    fn add(self, rhs: RHS) -> <Self as Add<RHS>>::Output;
}