[Bug c++/127627] What's the right overload resolution for ``public: X(const X&); private: explicit X(const X&) requires T::value = default;``?

[songb432 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127627

--- Comment #1 from songb432 at gmail dot com ---
<source>:15:15: error: no matching function for call to 'X<S>::X(const X<S>&)'
   15 |     X<S> x2 = x;
      |               ^
  • there are 2 candidates
    • candidate 1: 'constexpr X<T>::X() [with T = S]'
      <source>:4:3:
          4 |   X() = default;
            |   ^
      • candidate expects 0 arguments, 1 provided
    • candidate 2: 'constexpr X<T>::X(const X<T>&) requires  T::value [with T =
S]' (ignored)
      <source>:7:12:
          7 |   explicit X(const X&) requires (T::value) = default;
            |            ^


Where is ``candidate 1.5: 'X<T>::X(const X<T>&)'`` ?