[Bug c++/70395] New: [C++11] Error when initializing array of non-copyable non-trivial type in constructor initializer list

[mosra at centrum dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70395

            Bug ID: 70395
           Summary: [C++11] Error when initializing array of non-copyable
                    non-trivial type in constructor initializer list
           Product: gcc
           Version: 5.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mosra at centrum dot cz
  Target Milestone: ---

I am getting an error when trying to compile the following snippet:

    struct NonCopyable {
        NonCopyable(const NonCopyable&) = delete;
        NonCopyable(NonCopyable&&) = delete;
        NonCopyable& operator=(const NonCopyable&) = delete;
        NonCopyable& operator=(NonCopyable&&) = delete;

        NonCopyable() {}

        ~NonCopyable() {} // to make it non-trivial
    };

    union A {
        A(): _a{} {}
        ~A() {}

        NonCopyable _a[5];
    } a;

    int main() {}

GCC 5.3 complains that `error: use of deleted function
‘NonCopyable::NonCopyable(NonCopyable&&)’`, both Clang 3.7 and MSVC 2015
compile fine. I really don't see why it should use a move constructor for
initializing the elements. The behavior differs when I make the following
changes:

- If I make the `_a` member a non-array, it compiles fine.
- If I remove the `NonCopyable` destructor, the struct is trivial again and
everything compiles fine
- If I use placement new instead of `_a{}`, everything compiles fine (but
that's verbose)

The behavior is the same for struct and union, I used union to emphasize that I
need to do the initialization explicitly.

This probably affects also older versions, didn't have a chance to test.