Function rustc_abi::layout::layout_of_struct

fn layout_of_struct<'a, LC, FieldIdx: Idx, VariantIdx: Idx, F>(
    layout_calc: &LC,
    repr: &ReprOptions,
    variants: &IndexSlice<VariantIdx, IndexVec<FieldIdx, F>>,
    is_enum: bool,
    is_unsafe_cell: bool,
    scalar_valid_range: (Bound<u128>, Bound<u128>),
    always_sized: bool,
    dl: &TargetDataLayout,
    present_first: VariantIdx
) -> Option<LayoutS<FieldIdx, VariantIdx>>
where
    LC: LayoutCalculator + ?Sized,
    F: Deref<Target = &'a LayoutS<FieldIdx, VariantIdx>> + Debug,

single-variant enums are just structs, if you think about it