u8string_view unknown

[0-wiz-0]

After updating nlohmann-json in pkgsrc from 3.11.3 to 3.12.0, openrct2 stopped building:

https://releng.netbsd.org/pkgreports/shadow/HEAD/NetBSD-10.0-x86_64/20250425.1835/openrct2-0.4.21nb2/build.log

with the error:

/usr/pkg/include/nlohmann/detail/conversions/from_json.hpp:544:27: error: 'u8string_view' is not a member of 'std'; did you mean 'wstring_view'?

I see that other places include <string_view> depending on if JSON_HAS_CPP_17, but that is not the case in detail/conversions/from_json.hpp, so I suspect this is an error here.

Comments?

[nlohmann]

Yes, this seems to be introduced in #4631. I will add a PR.

[nlohmann]

Please check if #4763 fixes the issue.

[0-wiz-0]

Thank you for the analysis and patch!
It looks like this should have fixed the problem, but it doesn't :-(

In file included from /usr/pkg/include/nlohmann/adl_serializer.hpp:14,                                                                                                                                                                                21:40:44 [103/1923]
                 from /usr/pkg/include/nlohmann/json.hpp:34,
                 from /scratch/games/openrct2/work/OpenRCT2-0.4.21/src/openrct2/core/Json.hpp:14,
                 from /scratch/games/openrct2/work/OpenRCT2-0.4.21/src/openrct2/CommandLineSprite.cpp:17:
/usr/pkg/include/nlohmann/detail/conversions/from_json.hpp: In function 'void nlohmann::json_abi_v3_12_0::detail::from_json(const BasicJsonType&, std::filesystem::__cxx11::path&)':
/usr/pkg/include/nlohmann/detail/conversions/from_json.hpp:548:27: error: 'u8string_view' is not a member of 'std'; did you mean 'wstring_view'?
  548 |     p = std_fs::path(std::u8string_view(reinterpret_cast<const char8_t*>(s.data()), s.size()));
      |                           ^~~~~~~~~~~~~
      |                           wstring_view
/usr/pkg/include/nlohmann/detail/conversions/from_json.hpp:548:64: error: 'char8_t' was not declared in this scope; did you mean 'wchar_t'?
  548 |     p = std_fs::path(std::u8string_view(reinterpret_cast<const char8_t*>(s.data()), s.size()));
      |                                                                ^~~~~~~
      |                                                                wchar_t
/usr/pkg/include/nlohmann/detail/conversions/from_json.hpp:548:21: error: expected primary-expression before '(' token
  548 |     p = std_fs::path(std::u8string_view(reinterpret_cast<const char8_t*>(s.data()), s.size()));
      |                     ^
/usr/pkg/include/nlohmann/detail/conversions/from_json.hpp:548:27: error: 'u8string_view' is not a member of 'std'; did you mean 'wstring_view'?
  548 |     p = std_fs::path(std::u8string_view(reinterpret_cast<const char8_t*>(s.data()), s.size()));
      |                           ^~~~~~~~~~~~~
      |                           wstring_view
/usr/pkg/include/nlohmann/detail/conversions/from_json.hpp:548:64: error: expected '>' before 'char8_t'
  548 |     p = std_fs::path(std::u8string_view(reinterpret_cast<const char8_t*>(s.data()), s.size()));
      |                                                                ^~~~~~~
/usr/pkg/include/nlohmann/detail/conversions/from_json.hpp:548:64: error: expected '(' before 'char8_t'
  548 |     p = std_fs::path(std::u8string_view(reinterpret_cast<const char8_t*>(s.data()), s.size()));
      |                                                                ^~~~~~~
      |                                                                (
/usr/pkg/include/nlohmann/detail/conversions/from_json.hpp:548:72: error: expected primary-expression before '>' token
  548 |     p = std_fs::path(std::u8string_view(reinterpret_cast<const char8_t*>(s.data()), s.size()));
      |                                                                        ^
In file included from /usr/pkg/include/nlohmann/adl_serializer.hpp:15:
/usr/pkg/include/nlohmann/detail/conversions/to_json.hpp: In function 'void nlohmann::json_abi_v3_12_0::detail::to_json(BasicJsonType&, const std::filesystem::__cxx11::path&)':
/usr/pkg/include/nlohmann/detail/conversions/to_json.hpp:447:16: error: 'u8string' in namespace 'std' does not name a type
  447 |     const std::u8string s = p.u8string();
      |                ^~~~~~~~
/usr/pkg/include/nlohmann/detail/conversions/to_json.hpp:26:1: note: 'std::u8string' is defined in header '<string>'; did you forget to '#include <string>'?
   25 | #include <nlohmann/detail/iterators/iteration_proxy.hpp>
  +++ |+#include <string>
   26 | #include <nlohmann/detail/meta/cpp_future.hpp>
/usr/pkg/include/nlohmann/detail/conversions/to_json.hpp:448:21: error: 's' was not declared in this scope
  448 |     j = std::string(s.begin(), s.end());
      |                     ^

In case it matters, here's the command line used for compiling this file in openrct2:

g++ -fstack-protector-all -D_FORTIFY_SOURCE=2 -Wl,-zrelro -Wl,-znow -fPIC '-DDOCDIR="/usr/pkg/share/doc/openrct2"' -DOPENGL_NO_LINK -D_FILE_OFFSET_BITS=64 -D__WARN_SUGGEST_FINAL_METHODS__ -__WARN_SUGGEST_FINAL_TYPES__ -I/scratch/games/openrct2/work/OpenRCT2-0.4.21/src/openrct2/../thirdparty/duktape -I/scratch/games/openrct2/work/OpenRCT2-0.4.21/libopenrct2 -isystem /scratch/games/openrct2/work/.buildlink/include -isystem /scratch/games/openrct2/work/.buildlink/include/freetype2 -isystem /scratch/games/openrct2/work/.buildlink/include/libpng16 -isystem /scratch/games/openrct2/work/OpenRCT2-0.4.21/src/openrct2/../thirdparty -O2 -g -fstack-clash-protection -I/scratch/games/openrct2/work/.buildlink/include -I/scratch/games/openrct2/work/.buildlink/include/SDL2 -I/scratch/games/openrct2/work/.buildlink/include/libdrm -I/scratch/games/openrct2/work/.buildlink/include/freetype2 -I/scratch/games/openrct2/work/.buildlink/include/libxml2 '-DORCT2_RESOURCE_DIR="/usr/pkg/share/openrct2"' -fstrict-overflow -fstrict-aliasing -Wundef -Wmissing-declarations -Winit-self -Wall -Wextra -Wshadow -Wno-unknown-pragmas -Wno-missing-braces -Wno-comment -Wnonnull -Wno-unused-parameter -Wno-attributes -DDEBUG=0 -fno-char8_t -Wno-deprecated-declarations -DNDEBUG -std=gnu++20 -fPIC -Wsuggest-override -Wduplicated-cond -Wnon-virtual-dtor -Wduplicated-branches -Wrestrict -Wmissing-field-initializers -Wlogical-op -Wold-style-cast -Wunused-const-variable=1 -Wno-clobbered -Wredundant-decls -Wnull-dereference -Wsuggest-final-types -Wsuggest-final-methods -Wignored-qualifiers -Wstrict-overflow=1 -DENABLE_SCRIPTING -pthread -MD -MT CMakeFiles/libopenrct2.dir/src/openrct2/CommandLineSprite.cpp.o -MF CMakeFiles/libopenrct2.dir/src/openrct2/CommandLineSprite.cpp.o.d -o CMakeFiles/libopenrct2.dir/src/openrct2/CommandLineSprite.cpp.o -c /scratch/games/openrct2/work/OpenRCT2-0.4.21/src/openrct2/CommandLineSprite.cpp -std=c++20

(The buildlink paths are there because we like to avoid including installed-but-not-listed headers from compilation in pkgsrc.)

[nlohmann]

I think the issue is -fno-char8_t. This seems to be an oversight of #4736.

[nlohmann]

Did you check the latest develop branch? Because #4736 added this:

#if defined(__cpp_lib_char8_t) && (__cpp_lib_char8_t >= 201907L)
    p = std_fs::path(std::u8string_view(reinterpret_cast<const char8_t*>(s.data()), s.size()));
#else
    p = std_fs::u8path(s); // accepts UTF-8 encoded std::string in C++17, deprecated in C++20
#endif

so std::u8string_view should only be used if it is available.

[0-wiz-0]

Sorry, no, I just took the patch from #4763 on top of the last release. I'll add #4736 too. (If that doesn't work, I'll try development-head, which is a bit more effort for me than adding patches.).

[0-wiz-0]

You were right, adding #4736 fixed the problem.
Thank you for the fast help!