Function required_region_bounds

pub(crate) fn required_region_bounds<'tcx>(
    tcx: TyCtxt<'tcx>,
    erased_self_ty: Ty<'tcx>,
    predicates: impl Iterator<Item = Clause<'tcx>>,
) -> Vec<Region<'tcx>>

Given a set of predicates that apply to an object type, returns the region bounds that the (erased) Self type must outlive. Precisely because the Self type is erased, the parameter erased_self_ty must be supplied to indicate what type has been used to represent Self in the predicates themselves. This should really be a unique type; FreshTy(0) is a popular choice.

N.B., in some cases, particularly around higher-ranked bounds, this function returns a kind of conservative approximation. That is, all regions returned by this function are definitely required, but there may be other region bounds that are not returned, as well as requirements like for<'a> T: 'a.

Requires that trait definitions have been processed so that we can elaborate predicates and walk supertraits.