gcc 13.1 -Wdangling-reference warnings

[AaronVanGeffen]

Getting a few more warnings on my end when compiling with gcc 13.1. I have disabled -Werror, so I can work around them, but we should look into these:

[95/190] Building CXX object src/OpenLoco/CMakeFiles/OpenLoco.dir/src/Vehicles/Routing.cpp.o
/home/aaron/Repositories/OpenLoco/OpenLoco/src/OpenLoco/src/Vehicles/Routing.cpp: In function ‘void OpenLoco::Vehicles::findAllUsableTrackPieces(const LocationOfInterest&, FilterFunction, LocationOfInterestHashMap&)’:
/home/aaron/Repositories/OpenLoco/OpenLoco/src/OpenLoco/src/Vehicles/Routing.cpp:554:29: warning: possibly dangling reference to a temporary [-Wdangling-reference]
  554 |                 const auto& targetPiece = World::TrackData::getTrackPiece(elTrack->trackId())[elTrack->sequenceIndex()];
      |                             ^~~~~~~~~~~
/home/aaron/Repositories/OpenLoco/OpenLoco/src/OpenLoco/src/Vehicles/Routing.cpp:554:119: note: the temporary was destroyed at the end of the full expression ‘OpenLoco::World::TrackData::getTrackPiece(((size_t)elTrack->OpenLoco::World::TrackElement::trackId())).nonstd::span_lite::span<const OpenLoco::World::TrackData::PreviewTrack>::operator[](((nonstd::span_lite::span<const OpenLoco::World::TrackData::PreviewTrack>::size_type)elTrack->OpenLoco::World::TrackElement::sequenceIndex()))’
  554 |                 const auto& targetPiece = World::TrackData::getTrackPiece(elTrack->trackId())[elTrack->sequenceIndex()];
      |                                                                                                                       ^
At global scope:
cc1plus: note: unrecognized command-line option ‘-Wno-unused-private-field’ may have been intended to silence earlier diagnostics
[115/190] Building CXX object src/OpenLoco/CMakeFiles/OpenLoco.dir/src/Windows/Construction/Common.cpp.o
/home/aaron/Repositories/OpenLoco/OpenLoco/src/OpenLoco/src/Windows/Construction/Common.cpp: In function ‘void OpenLoco::Ui::Windows::Construction::Common::setNextAndPreviousTrackTile(const OpenLoco::World::TrackElement&, const OpenLoco::World::Pos2&)’:
/home/aaron/Repositories/OpenLoco/OpenLoco/src/OpenLoco/src/Windows/Construction/Common.cpp:631:25: warning: possibly dangling reference to a temporary [-Wdangling-reference]
  631 |             const auto& piece = TrackData::getTrackPiece(elTrack.trackId())[elTrack.sequenceIndex()];
      |                         ^~~~~
/home/aaron/Repositories/OpenLoco/OpenLoco/src/OpenLoco/src/Windows/Construction/Common.cpp:631:100: note: the temporary was destroyed at the end of the full expression ‘OpenLoco::World::TrackData::getTrackPiece(((size_t)(& elTrack)->OpenLoco::World::TrackElement::trackId())).nonstd::span_lite::span<const OpenLoco::World::TrackData::PreviewTrack>::operator[](((nonstd::span_lite::span<const OpenLoco::World::TrackData::PreviewTrack>::size_type)(& elTrack)->OpenLoco::World::TrackElement::sequenceIndex()))’
  631 |             const auto& piece = TrackData::getTrackPiece(elTrack.trackId())[elTrack.sequenceIndex()];
      |                                                                                                    ^
/home/aaron/Repositories/OpenLoco/OpenLoco/src/OpenLoco/src/Windows/Construction/Common.cpp: In function ‘void OpenLoco::Ui::Windows::Construction::Common::setNextAndPreviousRoadTile(const OpenLoco::World::RoadElement&, const OpenLoco::World::Pos2&)’:
/home/aaron/Repositories/OpenLoco/OpenLoco/src/OpenLoco/src/Windows/Construction/Common.cpp:655:25: warning: possibly dangling reference to a temporary [-Wdangling-reference]
  655 |             const auto& piece = TrackData::getRoadPiece(elRoad.roadId())[elRoad.sequenceIndex()];
      |                         ^~~~~
/home/aaron/Repositories/OpenLoco/OpenLoco/src/OpenLoco/src/Windows/Construction/Common.cpp:655:96: note: the temporary was destroyed at the end of the full expression ‘OpenLoco::World::TrackData::getRoadPiece(((size_t)(& elRoad)->OpenLoco::World::RoadElement::roadId())).nonstd::span_lite::span<const OpenLoco::World::TrackData::PreviewTrack>::operator[](((nonstd::span_lite::span<const OpenLoco::World::TrackData::PreviewTrack>::size_type)(& elRoad)->OpenLoco::World::RoadElement::sequenceIndex()))’
  655 |             const auto& piece = TrackData::getRoadPiece(elRoad.roadId())[elRoad.sequenceIndex()];
      |                                                                                                ^
At global scope:
cc1plus: note: unrecognized command-line option ‘-Wno-unused-private-field’ may have been intended to silence earlier diagnostics
[140/190] Building CXX object src/OpenLoco/CMakeFiles/OpenLoco.dir/src/Windows/Options.cpp.o
/home/aaron/Repositories/OpenLoco/OpenLoco/src/OpenLoco/src/Windows/Options.cpp: In function ‘void OpenLoco::Ui::Windows::Options::Regional::prepareDraw(OpenLoco::Ui::Window&)’:
/home/aaron/Repositories/OpenLoco/OpenLoco/src/OpenLoco/src/Windows/Options.cpp:1351:19: warning: possibly dangling reference to a temporary [-Wdangling-reference]
 1351 |             auto& language = Localisation::getDescriptorForLanguage(Config::get().language);
      |                   ^~~~~~~~
/home/aaron/Repositories/OpenLoco/OpenLoco/src/OpenLoco/src/Windows/Options.cpp:1351:68: note: the temporary was destroyed at the end of the full expression ‘OpenLoco::Localisation::getDescriptorForLanguage(std::__cxx11::basic_string<char>(OpenLoco::Config::get().OpenLoco::Config::NewConfig::language))’
 1351 |             auto& language = Localisation::getDescriptorForLanguage(Config::get().language);
      |                              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
At global scope:
cc1plus: note: unrecognized command-line option ‘-Wno-unused-private-field’ may have been intended to silence earlier diagnostics

[AaronVanGeffen]

I'm getting these warnings in libfmt as well. Would it be an option to disable these warnings for libfmt exclusively, or perhaps even globally?

[duncanspumpkin]

I'm getting these warnings in libfmt as well. Would it be an option to disable these warnings for libfmt exclusively, or perhaps even globally?

we can just update libfmt fmtlib/fmt#3415

[AaronVanGeffen]

From that same thread:

GCC will temporarily move the warning to -Wextra

https://gcc.gnu.org/git/gitweb.cgi?p=gcc.git;h=6b927b1297e66e26e62e722bf15c921dcbbd25b9

Currently it's producing many false positives.

Hoping the next point release won't be too far off then.

[Brensom]

I have the same problem:

/home/qwerty/building/openloco/src/OpenLoco-23.06/src/Diagnostics/src/LogTerminal.cpp:68:36:   required from here
/home/qwerty/building/openloco/src/OpenLoco-23.06/build/_deps/fmt-src/include/fmt/core.h:1735:15: error: possibly dangling reference to a temporary [-Werror=dangling-reference]
 1735 |   const auto& arg = arg_mapper<Context>().map(FMT_FORWARD(val));
      |               ^~~
/home/qwerty/building/openloco/src/OpenLoco-23.06/build/_deps/fmt-src/include/fmt/core.h:1735:46: note: the temporary was destroyed at the end of the full expression ‘fmt::v9::detail::arg_mapper<fmt::v9::basic_format_context<fmt::v9::appender, char> >().fmt::v9::detail::arg_mapper<fmt::v9::basic_format_context<fmt::v9::appender, char> >::map<tm&>((* & val))’
 1735 |   const auto& arg = arg_mapper<Context>().map(FMT_FORWARD(val));
      |                     ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
In file included from /home/qwerty/building/openloco/src/OpenLoco-23.06/build/_deps/fmt-src/include/fmt/format.h:48,
                 from /home/qwerty/building/openloco/src/OpenLoco-23.06/src/Diagnostics/include/OpenLoco/Diagnostics/LogSink.h:4,
                 from /home/qwerty/building/openloco/src/OpenLoco-23.06/src/Diagnostics/include/OpenLoco/Diagnostics/LogFile.h:4,
                 from /home/qwerty/building/openloco/src/OpenLoco-23.06/src/Diagnostics/src/LogFile.cpp:1:
/home/qwerty/building/openloco/src/OpenLoco-23.06/build/_deps/fmt-src/include/fmt/core.h: In instantiation of ‘constexpr fmt::v9::detail::value<Context> fmt::v9::detail::make_value(T&&) [with Context = fmt::v9::basic_format_context<fmt::v9::appender, char>; T = tm&]’:
/home/qwerty/building/openloco/src/OpenLoco-23.06/build/_deps/fmt-src/include/fmt/core.h:1777:29:   required from ‘constexpr fmt::v9::detail::value<Context> fmt::v9::detail::make_arg(T&&) [with bool IS_PACKED = true; Context = fmt::v9::basic_format_context<fmt::v9::appender, char>; type <anonymous> = fmt::v9::detail::type::custom_type; T = tm&; typename std::enable_if<IS_PACKED, int>::type <anonymous> = 0]’
/home/qwerty/building/openloco/src/OpenLoco-23.06/build/_deps/fmt-src/include/fmt/core.h:1901:77:   required from ‘constexpr fmt::v9::format_arg_store<Context, Args>::format_arg_store(T&& ...) [with T = {tm&}; Context = fmt::v9::basic_format_context<fmt::v9::appender, char>; Args = {tm}]’
/home/qwerty/building/openloco/src/OpenLoco-23.06/build/_deps/fmt-src/include/fmt/core.h:1918:31:   required from ‘constexpr fmt::v9::format_arg_store<Context, typename std::remove_cv<typename std::remove_reference<Args>::type>::type ...> fmt::v9::make_format_args(Args&& ...) [with Context = basic_format_context<appender, char>; Args = {tm&}]’
/home/qwerty/building/openloco/src/OpenLoco-23.06/build/_deps/fmt-src/include/fmt/core.h:3206:44:   required from ‘std::string fmt::v9::format(format_string<T ...>, T&& ...) [with T = {tm}; std::string = std::__cxx11::basic_string<char>; format_string<T ...> = basic_format_string<char, tm>]’
/home/qwerty/building/openloco/src/OpenLoco-23.06/src/Diagnostics/src/LogFile.cpp:31:36:   required from here
/home/qwerty/building/openloco/src/OpenLoco-23.06/build/_deps/fmt-src/include/fmt/core.h:1735:15: error: possibly dangling reference to a temporary [-Werror=dangling-reference]
 1735 |   const auto& arg = arg_mapper<Context>().map(FMT_FORWARD(val));
      |               ^~~
/home/qwerty/building/openloco/src/OpenLoco-23.06/build/_deps/fmt-src/include/fmt/core.h:1735:46: note: the temporary was destroyed at the end of the full expression ‘fmt::v9::detail::arg_mapper<fmt::v9::basic_format_context<fmt::v9::appender, char> >().fmt::v9::detail::arg_mapper<fmt::v9::basic_format_context<fmt::v9::appender, char> >::map<tm&>((* & val))’
 1735 |   const auto& arg = arg_mapper<Context>().map(FMT_FORWARD(val));
      |                     ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
cc1plus: note: unrecognized command-line option ‘-Wno-unused-private-field’ may have been intended to silence earlier diagnostics
cc1plus: all warnings being treated as errors
make[2]: *** [src/Diagnostics/CMakeFiles/Diagnostics.dir/build.make:104: src/Diagnostics/CMakeFiles/Diagnostics.dir/src/LogTerminal.cpp.o] Error 1
make[2]: *** Waiting for unfinished jobs....
cc1plus: note: unrecognized command-line option ‘-Wno-unused-private-field’ may have been intended to silence earlier diagnostics
cc1plus: all warnings being treated as errors
make[2]: *** [src/Diagnostics/CMakeFiles/Diagnostics.dir/build.make:76: src/Diagnostics/CMakeFiles/Diagnostics.dir/src/LogFile.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:579: src/Diagnostics/CMakeFiles/Diagnostics.dir/all] Error 2

[AaronVanGeffen]

@Brensom A workaround is to pass -DSTRICT=Off when invoking cmake. That will disable -Werror, so compiling should work at least.

[AaronVanGeffen]

These have all been addressed in the past week, I believe.