Function rustc_hir_analysis::impl_wf_check::min_specialization::unconstrained_parent_impl_substs

fn unconstrained_parent_impl_substs<'tcx>(
    tcx: TyCtxt<'tcx>,
    impl_def_id: DefId,
    impl_substs: SubstsRef<'tcx>
) -> Vec<GenericArg<'tcx>>

Returns a list of all of the unconstrained subst of the given impl.

For example given the impl:

impl<’a, T, I> … where &’a I: IntoIterator<Item=&’a T>

This would return the substs corresponding to ['a, I], because knowing 'a and I determines the value of T.