[Bug c++/112839] New: Unable to default initialize member variable in specific circumstances

["luigighiron at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112839

            Bug ID: 112839
           Summary: Unable to default initialize member variable in
                    specific circumstances
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: luigighiron at gmail dot com
  Target Milestone: ---

The following code is not accepted by GCC:

struct A {
    struct B {
        int C = 0;
    };
    A() = default;
    A(int) {}
    std::pair<B, B> p;
};

The error message generated indicates that it was unable to find a constructor
to call in the constructor A(int).

Doing any of the following seems to remove the error:
1. Removing the constructor A()
2. Explicitly define the constructor A()
3. Defining a default constructor for B (that isn't defaulted)
4. Removing the default value from C
5. Initializing p when it is being declared, i.e. std::pair<B, B> p{};
6. Defining B outside of the class
7. Using a non-default constructor in the member initializer list

Clang, MSVC, and old versions of GCC (version 8, version 5, and version 4)
accept this code.