Tests fail to compile (GCC 14)

[musicinmybrain]

Using GCC 14.2.1 in Fedora 41, the current master 7503c54 fails to compile:

$ git clone https://github.com/martinmoene/variant-lite.git
$ cd variant-lite
$ cmake -S. -Bbuild
$ cmake --build build --verbose
[…]
[ 91%] Building CXX object test/CMakeFiles/variant-lite-cpp17.t.dir/variant.t.cpp.o
cd /home/ben/src/forks/variant-lite/build/test && /usr/bin/c++ -Dvariant_CONFIG_SELECT_VARIANT=variant_VARIANT_DEFAULT -I/home/ben/src/forks/variant-lite/test/. -I/home/ben/src/forks/variant-lite/include -isystem /home/ben/src/forks/variant-lite/test/lest -Wall -Wextra -Wconversion -Wsign-conversion -Wno-missing-braces -fno-elide-constructors -std=c++17 -MD -MT test/CMakeFiles/variant-lite-cpp17.t.dir/variant.t.cpp.o -MF CMakeFiles/variant-lite-cpp17.t.dir/variant.t.cpp.o.d -o CMakeFiles/variant-lite-cpp17.t.dir/variant.t.cpp.o -c /home/ben/src/forks/variant-lite/test/variant.t.cpp
/home/ben/src/forks/variant-lite/test/variant.t.cpp: In function ‘void __lest_function__520(lest::env&)’:
/home/ben/src/forks/variant-lite/test/variant.t.cpp:525:43: error: no matching function for call to ‘std::variant<double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >::variant(int&)’
  525 |     variant<double, std::string> var1(  i );
      |                                           ^
In file included from /home/ben/src/forks/variant-lite/include/nonstd/variant.hpp:214,
                 from /home/ben/src/forks/variant-lite/test/variant-main.t.hpp:13,
                 from /home/ben/src/forks/variant-lite/test/variant.t.cpp:8:
/usr/include/c++/14/variant:1487:9: note: candidate: ‘template<long unsigned int _Np, class _Up, class ... _Args, class _Tp, class> constexpr std::variant<_Types>::variant(std::in_place_index_t<_Np>, std::initializer_list<_Up>, _Args&& ...) [with long unsigned int _Np = _Np; _Args = _Up; _Tp = {_Args ...}; <template-parameter-2-5> = _Tp; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1487 |         variant(in_place_index_t<_Np>, initializer_list<_Up> __il,
      |         ^~~~~~~
/usr/include/c++/14/variant:1487:9: note:   candidate expects at least 2 arguments, 1 provided
/usr/include/c++/14/variant:1477:9: note: candidate: ‘template<long unsigned int _Np, class ... _Args, class _Tp, class> constexpr std::variant<_Types>::variant(std::in_place_index_t<_Np>, _Args&& ...) [with long unsigned int _Np = _Np; _Args = {_Args ...}; <template-parameter-2-4> = _Tp; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1477 |         variant(in_place_index_t<_Np>, _Args&&... __args)
      |         ^~~~~~~
/usr/include/c++/14/variant:1477:9: note:   template argument deduction/substitution failed:
/home/ben/src/forks/variant-lite/test/variant.t.cpp:525:43: note:   mismatched types ‘std::in_place_index_t<_Idx>’ and ‘int’
  525 |     variant<double, std::string> var1(  i );
      |                                           ^
/usr/include/c++/14/variant:1467:9: note: candidate: ‘template<class _Tp, class _Up, class ... _Args, class> constexpr std::variant<_Types>::variant(std::in_place_type_t<_Tp>, std::initializer_list<_Up>, _Args&& ...) [with _Up = _Tp; _Args = _Up; <template-parameter-2-4> = {_Args ...}; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1467 |         variant(in_place_type_t<_Tp>, initializer_list<_Up> __il,
      |         ^~~~~~~
/usr/include/c++/14/variant:1467:9: note:   candidate expects at least 2 arguments, 1 provided
/usr/include/c++/14/variant:1457:9: note: candidate: ‘template<class _Tp, class ... _Args, class> constexpr std::variant<_Types>::variant(std::in_place_type_t<_Tp>, _Args&& ...) [with _Args = _Tp; <template-parameter-2-3> = {_Args ...}; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1457 |         variant(in_place_type_t<_Tp>, _Args&&... __args)
      |         ^~~~~~~
/usr/include/c++/14/variant:1457:9: note:   template argument deduction/substitution failed:
/home/ben/src/forks/variant-lite/test/variant.t.cpp:525:43: note:   mismatched types ‘std::in_place_type_t<_Tp>’ and ‘int’
  525 |     variant<double, std::string> var1(  i );
      |                                           ^
/usr/include/c++/14/variant:1447:9: note: candidate: ‘template<class _Tp, class, class, class _Tj, class> constexpr std::variant<_Types>::variant(_Tp&&) [with <template-parameter-2-2> = _Tp; _Tj = <template-parameter-1-2>; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1447 |         variant(_Tp&& __t)
      |         ^~~~~~~
/usr/include/c++/14/variant:1447:9: note:   template argument deduction/substitution failed:
/usr/include/c++/14/variant: In substitution of ‘template<class ... _Types> template<class _Tp, class> using std::variant<_Types>::__accepted_type = std::variant<_Types>::__to_type<((long unsigned int)__accepted_index<_Tp>)> [with _Tp = int&; <template-parameter-2-2> = void; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’:
/usr/include/c++/14/variant:1443:9:   required from here
 1443 |                typename _Tj = __accepted_type<_Tp&&>,
      |                ^~~~~~~~
/usr/include/c++/14/variant:1403:15: error: no type named ‘type’ in ‘struct std::enable_if<false, void>’
 1403 |         using __accepted_type = __to_type<__accepted_index<_Tp>>;
      |               ^~~~~~~~~~~~~~~
/usr/include/c++/14/variant:1430:9: note: candidate: ‘template<class _Tp0, class> constexpr std::variant<_Types>::variant() [with <template-parameter-2-2> = _Tp0; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1430 |         variant() noexcept(is_nothrow_default_constructible_v<__to_type<0>>)
      |         ^~~~~~~
/usr/include/c++/14/variant:1430:9: note:   candidate expects 0 arguments, 1 provided
/usr/include/c++/14/variant:1435:7: note: candidate: ‘std::variant<_Types>::variant(std::variant<_Types>&&) [with _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1435 |       variant(variant&&) = default;
      |       ^~~~~~~
/usr/include/c++/14/variant:1435:15: note:   no known conversion for argument 1 from ‘int’ to ‘std::variant<double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >&&’
 1435 |       variant(variant&&) = default;
      |               ^~~~~~~~~
/usr/include/c++/14/variant:1434:7: note: candidate: ‘std::variant<_Types>::variant(const std::variant<_Types>&) [with _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1434 |       variant(const variant& __rhs) = default;
      |       ^~~~~~~
/usr/include/c++/14/variant:1434:30: note:   no known conversion for argument 1 from ‘int’ to ‘const std::variant<double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >&’
 1434 |       variant(const variant& __rhs) = default;
      |               ~~~~~~~~~~~~~~~^~~~~
/home/ben/src/forks/variant-lite/test/variant.t.cpp:526:43: error: no matching function for call to ‘std::variant<double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >::variant(int)’
  526 |     variant<double, std::string> var2(  7 );
      |                                           ^
/usr/include/c++/14/variant:1487:9: note: candidate: ‘template<long unsigned int _Np, class _Up, class ... _Args, class _Tp, class> constexpr std::variant<_Types>::variant(std::in_place_index_t<_Np>, std::initializer_list<_Up>, _Args&& ...) [with long unsigned int _Np = _Np; _Args = _Up; _Tp = {_Args ...}; <template-parameter-2-5> = _Tp; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1487 |         variant(in_place_index_t<_Np>, initializer_list<_Up> __il,
      |         ^~~~~~~
/usr/include/c++/14/variant:1487:9: note:   candidate expects at least 2 arguments, 1 provided
/usr/include/c++/14/variant:1477:9: note: candidate: ‘template<long unsigned int _Np, class ... _Args, class _Tp, class> constexpr std::variant<_Types>::variant(std::in_place_index_t<_Np>, _Args&& ...) [with long unsigned int _Np = _Np; _Args = {_Args ...}; <template-parameter-2-4> = _Tp; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1477 |         variant(in_place_index_t<_Np>, _Args&&... __args)
      |         ^~~~~~~
/usr/include/c++/14/variant:1477:9: note:   template argument deduction/substitution failed:
/home/ben/src/forks/variant-lite/test/variant.t.cpp:526:43: note:   mismatched types ‘std::in_place_index_t<_Idx>’ and ‘int’
  526 |     variant<double, std::string> var2(  7 );
      |                                           ^
/usr/include/c++/14/variant:1467:9: note: candidate: ‘template<class _Tp, class _Up, class ... _Args, class> constexpr std::variant<_Types>::variant(std::in_place_type_t<_Tp>, std::initializer_list<_Up>, _Args&& ...) [with _Up = _Tp; _Args = _Up; <template-parameter-2-4> = {_Args ...}; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1467 |         variant(in_place_type_t<_Tp>, initializer_list<_Up> __il,
      |         ^~~~~~~
/usr/include/c++/14/variant:1467:9: note:   candidate expects at least 2 arguments, 1 provided
/usr/include/c++/14/variant:1457:9: note: candidate: ‘template<class _Tp, class ... _Args, class> constexpr std::variant<_Types>::variant(std::in_place_type_t<_Tp>, _Args&& ...) [with _Args = _Tp; <template-parameter-2-3> = {_Args ...}; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1457 |         variant(in_place_type_t<_Tp>, _Args&&... __args)
      |         ^~~~~~~
/usr/include/c++/14/variant:1457:9: note:   template argument deduction/substitution failed:
/home/ben/src/forks/variant-lite/test/variant.t.cpp:526:43: note:   mismatched types ‘std::in_place_type_t<_Tp>’ and ‘int’
  526 |     variant<double, std::string> var2(  7 );
      |                                           ^
/usr/include/c++/14/variant:1447:9: note: candidate: ‘template<class _Tp, class, class, class _Tj, class> constexpr std::variant<_Types>::variant(_Tp&&) [with <template-parameter-2-2> = _Tp; _Tj = <template-parameter-1-2>; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1447 |         variant(_Tp&& __t)
      |         ^~~~~~~
/usr/include/c++/14/variant:1447:9: note:   template argument deduction/substitution failed:
/usr/include/c++/14/variant: In substitution of ‘template<class ... _Types> template<class _Tp, class> using std::variant<_Types>::__accepted_type = std::variant<_Types>::__to_type<((long unsigned int)__accepted_index<_Tp>)> [with _Tp = int&&; <template-parameter-2-2> = void; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’:
/usr/include/c++/14/variant:1443:9:   required from here
 1443 |                typename _Tj = __accepted_type<_Tp&&>,
      |                ^~~~~~~~
/usr/include/c++/14/variant:1403:15: error: no type named ‘type’ in ‘struct std::enable_if<false, void>’
 1403 |         using __accepted_type = __to_type<__accepted_index<_Tp>>;
      |               ^~~~~~~~~~~~~~~
/usr/include/c++/14/variant:1430:9: note: candidate: ‘template<class _Tp0, class> constexpr std::variant<_Types>::variant() [with <template-parameter-2-2> = _Tp0; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1430 |         variant() noexcept(is_nothrow_default_constructible_v<__to_type<0>>)
      |         ^~~~~~~
/usr/include/c++/14/variant:1430:9: note:   candidate expects 0 arguments, 1 provided
/usr/include/c++/14/variant:1435:7: note: candidate: ‘std::variant<_Types>::variant(std::variant<_Types>&&) [with _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1435 |       variant(variant&&) = default;
      |       ^~~~~~~
/usr/include/c++/14/variant:1435:15: note:   no known conversion for argument 1 from ‘int’ to ‘std::variant<double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >&&’
 1435 |       variant(variant&&) = default;
      |               ^~~~~~~~~
/usr/include/c++/14/variant:1434:7: note: candidate: ‘std::variant<_Types>::variant(const std::variant<_Types>&) [with _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1434 |       variant(const variant& __rhs) = default;
      |       ^~~~~~~
/usr/include/c++/14/variant:1434:30: note:   no known conversion for argument 1 from ‘int’ to ‘const std::variant<double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >&’
 1434 |       variant(const variant& __rhs) = default;
      |               ~~~~~~~~~~~~~~~^~~~~
/home/ben/src/forks/variant-lite/test/variant.t.cpp: In function ‘void __lest_function__538(lest::env&)’:
/home/ben/src/forks/variant-lite/test/variant.t.cpp:544:45: error: no matching function for call to ‘std::variant<double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >::variant(__lest_function__538(lest::env&)::Int)’
  544 |     variant<double, std::string> var( Int{} );
      |                                             ^
/usr/include/c++/14/variant:1487:9: note: candidate: ‘template<long unsigned int _Np, class _Up, class ... _Args, class _Tp, class> constexpr std::variant<_Types>::variant(std::in_place_index_t<_Np>, std::initializer_list<_Up>, _Args&& ...) [with long unsigned int _Np = _Np; _Args = _Up; _Tp = {_Args ...}; <template-parameter-2-5> = _Tp; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1487 |         variant(in_place_index_t<_Np>, initializer_list<_Up> __il,
      |         ^~~~~~~
/usr/include/c++/14/variant:1487:9: note:   candidate expects at least 2 arguments, 1 provided
/usr/include/c++/14/variant:1477:9: note: candidate: ‘template<long unsigned int _Np, class ... _Args, class _Tp, class> constexpr std::variant<_Types>::variant(std::in_place_index_t<_Np>, _Args&& ...) [with long unsigned int _Np = _Np; _Args = {_Args ...}; <template-parameter-2-4> = _Tp; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1477 |         variant(in_place_index_t<_Np>, _Args&&... __args)
      |         ^~~~~~~
/usr/include/c++/14/variant:1477:9: note:   template argument deduction/substitution failed:
/home/ben/src/forks/variant-lite/test/variant.t.cpp:544:45: note:   ‘__lest_function__538(lest::env&)::Int’ is not derived from ‘std::in_place_index_t<_Idx>’
  544 |     variant<double, std::string> var( Int{} );
      |                                             ^
/usr/include/c++/14/variant:1467:9: note: candidate: ‘template<class _Tp, class _Up, class ... _Args, class> constexpr std::variant<_Types>::variant(std::in_place_type_t<_Tp>, std::initializer_list<_Up>, _Args&& ...) [with _Up = _Tp; _Args = _Up; <template-parameter-2-4> = {_Args ...}; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1467 |         variant(in_place_type_t<_Tp>, initializer_list<_Up> __il,
      |         ^~~~~~~
/usr/include/c++/14/variant:1467:9: note:   candidate expects at least 2 arguments, 1 provided
/usr/include/c++/14/variant:1457:9: note: candidate: ‘template<class _Tp, class ... _Args, class> constexpr std::variant<_Types>::variant(std::in_place_type_t<_Tp>, _Args&& ...) [with _Args = _Tp; <template-parameter-2-3> = {_Args ...}; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1457 |         variant(in_place_type_t<_Tp>, _Args&&... __args)
      |         ^~~~~~~
/usr/include/c++/14/variant:1457:9: note:   template argument deduction/substitution failed:
/home/ben/src/forks/variant-lite/test/variant.t.cpp:544:45: note:   ‘__lest_function__538(lest::env&)::Int’ is not derived from ‘std::in_place_type_t<_Tp>’
  544 |     variant<double, std::string> var( Int{} );
      |                                             ^
/usr/include/c++/14/variant:1447:9: note: candidate: ‘template<class _Tp, class, class, class _Tj, class> constexpr std::variant<_Types>::variant(_Tp&&) [with <template-parameter-2-2> = _Tp; _Tj = <template-parameter-1-2>; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1447 |         variant(_Tp&& __t)
      |         ^~~~~~~
/usr/include/c++/14/variant:1447:9: note:   template argument deduction/substitution failed:
/usr/include/c++/14/variant: In substitution of ‘template<class ... _Types> template<class _Tp, class> using std::variant<_Types>::__accepted_type = std::variant<_Types>::__to_type<((long unsigned int)__accepted_index<_Tp>)> [with _Tp = __lest_function__538(lest::env&)::Int&&; <template-parameter-2-2> = void; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’:
/usr/include/c++/14/variant:1443:9:   required from here
 1443 |                typename _Tj = __accepted_type<_Tp&&>,
      |                ^~~~~~~~
/usr/include/c++/14/variant:1403:15: error: no type named ‘type’ in ‘struct std::enable_if<false, void>’
 1403 |         using __accepted_type = __to_type<__accepted_index<_Tp>>;
      |               ^~~~~~~~~~~~~~~
/usr/include/c++/14/variant:1430:9: note: candidate: ‘template<class _Tp0, class> constexpr std::variant<_Types>::variant() [with <template-parameter-2-2> = _Tp0; _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1430 |         variant() noexcept(is_nothrow_default_constructible_v<__to_type<0>>)
      |         ^~~~~~~
/usr/include/c++/14/variant:1430:9: note:   candidate expects 0 arguments, 1 provided
/usr/include/c++/14/variant:1435:7: note: candidate: ‘std::variant<_Types>::variant(std::variant<_Types>&&) [with _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1435 |       variant(variant&&) = default;
      |       ^~~~~~~
/usr/include/c++/14/variant:1435:15: note:   no known conversion for argument 1 from ‘__lest_function__538(lest::env&)::Int’ to ‘std::variant<double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >&&’
 1435 |       variant(variant&&) = default;
      |               ^~~~~~~~~
/usr/include/c++/14/variant:1434:7: note: candidate: ‘std::variant<_Types>::variant(const std::variant<_Types>&) [with _Types = {double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’
 1434 |       variant(const variant& __rhs) = default;
      |       ^~~~~~~
/usr/include/c++/14/variant:1434:30: note:   no known conversion for argument 1 from ‘__lest_function__538(lest::env&)::Int’ to ‘const std::variant<double, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >&’
 1434 |       variant(const variant& __rhs) = default;
      |               ~~~~~~~~~~~~~~~^~~~~
gmake[2]: *** [test/CMakeFiles/variant-lite-cpp17.t.dir/build.make:93: test/CMakeFiles/variant-lite-cpp17.t.dir/variant.t.cpp.o] Error 1
gmake[2]: Leaving directory '/home/ben/src/forks/variant-lite/build'
gmake[1]: *** [CMakeFiles/Makefile2:208: test/CMakeFiles/variant-lite-cpp17.t.dir/all] Error 2
gmake[1]: Leaving directory '/home/ben/src/forks/variant-lite/build'
gmake: *** [Makefile:146: all] Error 2 

If I git checkout v2.0.0 and try again, the result is similar.

[Titaniumtown]

I can reproduce on nix in the process of packaging it: NixOS/nixpkgs#372723

[musicinmybrain]

In the package review for Fedora, Benson Muite pointed out that the tests only fail to compile in C++17 mode, so I’m working around this for the time being by hacking up test/CMakeLists.txt to pretend that C++17 mode is unavailable. At least that way I can still run the tests in C++98, C++11, and C++14 modes.

[martinmoene]

With PR #56 merged, the tests should now also compile with C++17/std::variant.

[martinmoene]

Tests updated for use with std::variant in Release 3.0.0