ICE: escaping regions in predicate Obligation(...)

[Manishearth]

#![feature(conservative_impl_trait)]


fn iter_values(a: &[u32]) -> impl Iterator<Item=&u32>{
    a.iter().map(|a| &a)
}

(playpen )

throws

   Compiling playground v0.0.1 (file:///playground)
error: internal compiler error: /checkout/src/librustc_typeck/check/mod.rs:618: escaping regions in predicate Obligation(predicate=Binder(ProjectionPredicate(ProjectionTy { substs: Slice([_]), item_def_id: DefId { krate: CrateNum(2), node: DefIndex(1591) => core/e78183f::iter[0]::iterator[0]::Iterator[0]::Item[0] } }, &u32)),depth=0)
  --> src/main.rs:21:30
   |
21 |     fn iter_values(&self) -> impl Iterator<Item=&u32>{
   |                              ^^^^^^^^^^^^^^^^^^^^^^^^

note: the compiler unexpectedly panicked. this is a bug.

[Manishearth]

cc @petrochenkov @eddyb

[kennytm]

Duplicate of #42479