[Bug c++/67342] New: Ill-formed move constructor ignored in favor of copy constructor

[Bug c++/67342] New: Ill-formed move constructor ignored in favor of copy constructor

[barry.revzin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67342

            Bug ID: 67342
           Summary: Ill-formed move constructor ignored in favor of copy
                    constructor
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: barry.revzin at gmail dot com
  Target Milestone: ---

In the following code, A is neither movable nor copyable, and B has an A:

#include <utility>

struct A {
    A() { }
    A(A const&) = delete;
    A(A&& ) = delete;
};

struct B {
    A a;

    B() = default;
    B(B const& ) : a() { }
    B(B&& ) = default;
};

int main()
{
    B b1;
    B b2(std::move(b1));
}

I would expect the move constructor to be preferred and this code to fail to
compile (with some diagnostic relating to the deleted A&& constructor), but
instead gcc (and clang) prefers the copy constructor for b2 here and the code
compiles.

I suspect this is a compiler bug, as if I instead defaulted the copy
constructor, gcc issues a diagnostic about "error: use of deleted function
'B::B(B&&)'"

[Bug c++/67342] Ill-formed move constructor ignored in favor of copy constructor

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67342

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The compiler is correct, see [class.copy]/11.

B(B&&) is defaulted, so is defined as deleted, and "A defaulted move
constructor that is defined as deleted is ignored by overload resolution"

[Bug c++/67342] Ill-formed move constructor ignored in favor of copy constructor

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67342

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1402

[Bug c++/67342] Ill-formed move constructor ignored in favor of copy constructor

[barry.revzin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67342

--- Comment #3 from Barry Revzin <barry.revzin at gmail dot com> ---
Thanks! I was pretty sure I was wrong but couldn't figure out why.

Barry

On Mon, Aug 24, 2015, 2:29 PM redi at gcc dot gnu.org <
gcc-bugzilla@gcc.gnu.org> wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67342
>
> --- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
> http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1402
>
> --
> You are receiving this mail because:
> You reported the bug.
>