rustc cannot see impls for other lifetimes in presence of specific where clause

[djzin]

The following code fails to compile:

trait Foo {
    fn foo(&self) {}
}

fn fail<'a>() where &'a (): Foo {
    (&()).foo()
}

impl<'a> Foo for &'a () {}

fn main() {}

The temporary &() is deduced to have type &'a () because of the where clause. If this where clause is removed, the code compiles. For some reason the compiler cannot see that &() still implements Foo for other lifetimes because of this where clause.

n.b. this came from reducing this reddit post
https://www.reddit.com/r/rust/comments/5hm2b6/my_lifetime_snafu/

[bluss]

This looks like a duplicate of #38071

[hanna-kruppe]

I'm not sure if #38071 is a duplicate of #24066 but this looks like a duplicate of #24066 in any case.

[Mark-Simulacrum]

Closing in favor of #38071, which may be a duplicate of #24066, but since we're uncertain not closing both--these two issues (this and #38071) are highly likely to be identical, though.