Function fold_local_ptrs 

fn fold_local_ptrs(
    infcx: &mut InferCtxt<'_, '_, '_>,
    env: &mut TypeEnv<'_>,
    span: Span,
) -> InferResult

Fold local pointers implements roughly a rule like the following (for all local pointers) that converts the local pointers created via unfold_local_ptrs back into &mut.

      T1 <: T2
--------------------- [local-fold]
Γ, l:[<: T2] T1 => Γ