extraFieldLen

    fn extraFieldLen(field: anytype) usize {
        const Field = @TypeOf(field);
        return switch (@typeInfo(Field)) {
            .void => 0,
            .int => |info| switch (info.bits) {
                32 => 1,
                64 => 2,
                else => comptime unreachable,
            },
            .@"enum" => 1,
            .@"struct" => |info| switch (info.layout) {
                .@"packed" => switch (info.backing_integer.?) {
                    u32 => 1,
                    u64 => 2,
                    else => comptime unreachable,
                },
                .auto => switch (Field.storage) {
                    .flag_optional, .enum_optional => (@sizeOf(Field.Value) + 3) / 4,
                    .extended => 1,
                    .length_prefixed_list,
                    .flag_length_prefixed_list,
                    .flag_list,
                    => 1 + @divExact(@sizeOf(Field.Elem), @sizeOf(u32)) * field.slice.len,
                    .multi_list => 1 + field.mal.len * @typeInfo(Field.Elem).@"struct".field_names.len,
                    .union_list => Field.extraLen(field.len),
                    .flag_union => switch (field.u) {
                        inline else => |v| extraFieldLen(v),
                    },
                },
                .@"extern" => @divExact(@sizeOf(Field), @sizeOf(u32)),
            },
            else => @compileError("bad type: " ++ @typeName(Field)),
        };
    }