[Bug c++/86646] New: Special member function 'cannot be defaulted' if type alias is used

[programmer at posteo dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86646

            Bug ID: 86646
           Summary: Special member function 'cannot be defaulted' if type
                    alias is used
           Product: gcc
           Version: 7.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: programmer at posteo dot de
  Target Milestone: ---

GCC 7.3.0 (as well as 8.1 and 9.0 from godbolt.org) fails to compile the
following code:

//---
template<int N_>
struct Foo {
  static constexpr int N = N_;// this indirection causes the error
  using Self = Foo<N>;

  Foo(const Self&) = default;
};
//---



The error message reads

> file.cpp:6:22: error: ‘Foo<N_>::Foo(const Self&)’ cannot be defaulted



I used the following command line to obtain that error message:

> g++ -Wall -Wextra -std=c++11 file.cpp