[Bug c++/68709] New: incorrectly requiring move-constructibility when list-initializing a polymorphic array element of a class member

[richard-gccbugzilla at metafoo dot co.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68709

            Bug ID: 68709
           Summary: incorrectly requiring move-constructibility when
                    list-initializing a polymorphic array element of a
                    class member
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: richard-gccbugzilla at metafoo dot co.uk
  Target Milestone: ---

GCC incorrectly rejects this:

struct A { virtual ~A(); };
struct B {
  B();
  B(B &&) = delete;
  A middle_field;
};
struct C {
  C() : b{{}, {}} {}
  B b[2];
};

saying:

<stdin>: In constructor ‘C::C()’:
<stdin>:8:17: error: use of deleted function ‘B::B(B&&)’
<stdin>:4:3: note: declared here

This is bogus: C's constructor should not invoke the B move constructor.