Function rustc_trait_selection::traits::project::prune_cache_value_obligations

fn prune_cache_value_obligations<'a, 'tcx>(
    infcx: &'a InferCtxt<'a, 'tcx>, 
    result: &NormalizedTy<'tcx>
) -> NormalizedTy<'tcx>

If there are unresolved type variables, then we need to include any subobligations that bind them, at least until those type variables are fully resolved.