[Bug libstdc++/95915] New: std::variant doesn't like types with a defaulted virtual destructor

[Bug libstdc++/95915] New: std::variant doesn't like types with a defaulted virtual destructor

[ville.voutilainen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95915

            Bug ID: 95915
           Summary: std::variant doesn't like types with a defaulted
                    virtual destructor
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ville.voutilainen at gmail dot com
  Target Milestone: ---

>From Patrice Roy:

The following code compiled in C++17 but seems broken in C++20, at least
according the Clang and gcc:

#include <variant>
struct X {
   virtual ~X() = default;
};
int main() {
   std::variant<X> v;
}

This is because variant's storage uses an _Uninitialized type that hacks
around a compiler bug, where the type X above wasn't literal. Now that it
is, the hack breaks. Since variant's other base-layers handle triviality
of special member functions properly, this hack can now be removed.

[Bug libstdc++/95915] std::variant doesn't like types with a defaulted virtual destructor

[ville.voutilainen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95915

Ville Voutilainen <ville.voutilainen at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2020-06-26
             Status|UNCONFIRMED                 |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |ville.voutilainen at gmail dot com

[Bug libstdc++/95915] [10/11 Regression] std::variant doesn't like types with a defaulted virtual destructor

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95915

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|std::variant doesn't like   |[10/11 Regression]
                   |types with a defaulted      |std::variant doesn't like
                   |virtual destructor          |types with a defaulted
                   |                            |virtual destructor
      Known to work|                            |9.3.0
           Keywords|                            |rejects-valid
   Target Milestone|---                         |10.2
      Known to fail|                            |10.1.0, 11.0

[Bug libstdc++/95915] [10/11 Regression] std::variant doesn't like types with a defaulted virtual destructor

[ville.voutilainen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95915

--- Comment #1 from Ville Voutilainen <ville.voutilainen at gmail dot com> ---
Patch at https://gcc.gnu.org/pipermail/gcc-patches/2020-June/549030.html

[Bug libstdc++/95915] [10/11 Regression] std::variant doesn't like types with a defaulted virtual destructor

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95915

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Ville Voutilainen <ville@gcc.gnu.org>:

https://gcc.gnu.org/g:24b54628cfa95194a8de4071c28cb56e6e81c08e

commit r11-1698-g24b54628cfa95194a8de4071c28cb56e6e81c08e
Author: Ville Voutilainen <ville.voutilainen@gmail.com>
Date:   Mon Jun 29 00:36:38 2020 +0300

    PR libstdc++/95915

            PR libstdc++/95915
            * include/std/type_traits (is_literal_type, is_literal_type_v):
            Deprecate in C++17.
            * include/std/variant (_Uninitialized):
            Adjust the condition and the comment.
            * testsuite/20_util/is_literal_type/deprecated-1z.cc: New.
            *
testsuite/20_util/is_literal_type/requirements/explicit_instantiation.cc:
            Adjust.
            * testsuite/20_util/is_literal_type/requirements/typedefs.cc:
Likewise.
            * testsuite/20_util/is_literal_type/value.cc: Likewise.
            * testsuite/20_util/optional/constexpr/nullopt.cc:
            Use __is_literal_type directly.
            * testsuite/20_util/optional/nullopt.cc: Likewise.
            * testsuite/20_util/variable_templates_for_traits.cc: Adjust.
            * testsuite/20_util/variant/95915.cc: New.
            * testsuite/20_util/variant/compile.cc: Add new test.
            * testsuite/experimental/optional/constexpr/nullopt.cc:
            Use __is_literal_type directly.
            * testsuite/experimental/optional/nullopt.cc: Likewise.
            * testsuite/experimental/type_traits/value.cc: Adjust.
            * testsuite/util/testsuite_common_types.h:
            Use __is_literal_type directly.

[Bug libstdc++/95915] [10/11 Regression] std::variant doesn't like types with a defaulted virtual destructor

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95915

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Ville Voutilainen
<ville@gcc.gnu.org>:

https://gcc.gnu.org/g:deb9c51ca71d3cb507dd91ab8bfd8c1021effd9f

commit r10-8386-gdeb9c51ca71d3cb507dd91ab8bfd8c1021effd9f
Author: Ville Voutilainen <ville.voutilainen@gmail.com>
Date:   Mon Jun 29 00:36:38 2020 +0300

    PR libstdc++/95915

            PR libstdc++/95915
            * include/std/variant (_Uninitialized):
            Adjust the condition and the comment.
            * testsuite/20_util/variant/95915.cc: New.
            * testsuite/20_util/variant/compile.cc: Add new test.

    (cherry picked from commit 24b54628cfa95194a8de4071c28cb56e6e81c08e)

[Bug libstdc++/95915] [10/11 Regression] std::variant doesn't like types with a defaulted virtual destructor

[ville.voutilainen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95915

Ville Voutilainen <ville.voutilainen at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #4 from Ville Voutilainen <ville.voutilainen at gmail dot com> ---
Fixed.