Type parameters that appear in a trait object assoc type bindings are considered as "not constrained"

[japaric]

STR

#![crate_type = "lib"]
#![no_std]

trait Iterator {
    type Item;
}

impl<'a, T> Iterator for &'a mut (Iterator<Item=T> + 'a) {
//~^ error: the type parameter `T` is not constrained by the impl trait, self type, or predicates
    type Item = T;
}

T appears in Self (the trait object assoc type binding) so it should be considered as constrained, and this impl should be accepted. (Also I don't how we could impl<'a> Iterator for &'a mut (Iterator + 'a) { type Item = ??? } without the T type parameter)

Version

rustc 1.0.0-nightly (ed530d7a3 2015-01-16 22:41:16 +0000)

cc @nikomatsakis

[japaric]

Also this blocks a possible solution to #21361 (boxed iterators (trait objects) can't use the IteratorExt methods)

[nikomatsakis]

Problem is presumably that walk_ty doesn't walk the projections in trait reference

[japaric]

re #21361, I worked around the issue with #[old_impl_check], so this is no longer a blocker. In fact, the PR that fixes that issue has already been r+ed.