Merge "Add noexcept to missing places in expected.h"

  expected& operator=(const expected& rhs) = default;

  // Note for SFNAIE above applies to here as well

  expected& operator=(expected&& rhs) = default;

  expected& operator=(expected&& rhs) noexcept(

      std::is_nothrow_move_assignable_v<T>&& std::is_nothrow_move_assignable_v<E>) = default;

  template <class U = T _ENABLE_IF(

                !std::is_void_v<T> &&

  expected& operator=(const expected& rhs) = default;

  // Note for SFNAIE above applies to here as well

  expected& operator=(expected&& rhs) = default;

  expected& operator=(expected&& rhs) noexcept(std::is_nothrow_move_assignable_v<E>) = default;

  template<class G = E>

  expected& operator=(const unexpected<G>& rhs) {

 public:

  // constructors

  constexpr unexpected(const unexpected&) = default;

  constexpr unexpected(unexpected&&) = default;

  constexpr unexpected(unexpected&&) noexcept(std::is_nothrow_move_constructible_v<E>) = default;

  template <class Err = E _ENABLE_IF(

                std::is_constructible_v<E, Err> &&

  // assignment

  constexpr unexpected& operator=(const unexpected&) = default;

  constexpr unexpected& operator=(unexpected&&) = default;

  constexpr unexpected& operator=(unexpected&&) noexcept(std::is_nothrow_move_assignable_v<E>) =

      default;

  template<class Err = E>

  constexpr unexpected& operator=(const unexpected<Err>& rhs) {

    val_ = rhs.value();