Function rustc_abi::layout::format_field_niches

fn format_field_niches<'a, FieldIdx: Idx, VariantIdx: Idx, F: Deref<Target = &'a LayoutS<FieldIdx, VariantIdx>> + Debug>(
    layout: &LayoutS<FieldIdx, VariantIdx>,
    fields: &IndexSlice<FieldIdx, F>,
    dl: &TargetDataLayout
) -> String