Explanation for E0207 is about unused type, but is shown when type is used incorrectly

[kornelski]

I'm trying to use a reference in an associated type. Rust wants me to add lifetime annotations, but it doesn't tell me where exactly they are needed.

If I try such (invalid) code:

trait Tr {
    type Ty;
}

struct St;

impl<'a> Tr for St {
    type Ty = &'a u8;
}

I'm getting error:

error: the lifetime parameter 'a is not constrained by the impl trait, self type, or predicates E0207

The problem is E0207 only tells me to remove the lifetime, but I'm trying to add it, so the error explanation doesn't help me solve my problem.

Pinging #32777

---

rustc 1.10.0-nightly (2b79e05 2016-05-13)

[sanmai-NL]

What's the version of Rust you're using? Some notes about how to report bugs/issues here.