pub const Small = packed struct {
    has_tag_type: bool,
    has_captures_len: bool,
    has_body_len: bool,
    has_fields_len: bool,
    has_decls_len: bool,
    name_strategy: NameStrategy,
    layout: std.builtin.Type.ContainerLayout,
    /// has_tag_type | auto_enum_tag | result
    /// -------------------------------------
    ///    false     | false         |  union { }
    ///    false     | true          |  union(enum) { }
    ///    true      | true          |  union(enum(T)) { }
    ///    true      | false         |  union(T) { }
    auto_enum_tag: bool,
    any_aligned_fields: bool,
    _: u5 = undefined,
}