Function rustc_borrowck::diagnostics::bound_region_errors::try_extract_error_from_fulfill_cx

fn try_extract_error_from_fulfill_cx<'tcx>(
    fulfill_cx: Box<dyn TraitEngine<'tcx> + 'tcx>, 
    infcx: &InferCtxt<'_, 'tcx>, 
    placeholder_region: Region<'tcx>, 
    error_region: Option<Region<'tcx>>
) -> Option<DiagnosticBuilder<'tcx>>