Function dyn_self_ty 

pub fn dyn_self_ty<'tcx>(
    tcx: TyCtxt<'tcx>,
    typing_env: TypingEnv<'tcx>,
    tref: TraitRef<'tcx>,
) -> Option<Ty<'tcx>>

Generates a dyn Trait<Args.., Ty = <Self as Trait>::Ty..> type for the given trait ref.