compilation problem with nvidia 25.3

[VictorEijkhout]

[ 46%] Building CXX object tests/CMakeFiles/test-iterators2_cpp20.dir/src/unit-iterators2.cpp.o
cd /work2/00434/eijkhout/json/build-3.12.0-stampede3-nvidia25.3/tests && /home1/apps/nvidia/Linux_x86_64/25.3/compilers/bin/nvc++ -DDOCTEST_CONFIG_SUPER_FAST_ASSERTS -DJSON_TEST_KEEP_MACROS -DJSON_TEST_USING_MULTIPLE_HEADERS=1 -I/work2/00434/eijkhout/json/json-3.12.0/tests/thirdparty/doctest -I/work2/00434/eijkhout/json/json-3.12.0/tests/thirdparty/fifo_map -I/work2/00434/eijkhout/json/build-3.12.0-stampede3-nvidia25.3/include -I/work2/00434/eijkhout/json/json-3.12.0/include -O2 -gopt -std=gnu++20 -Wno-deprecated -Wno-float-equal -MD -MT tests/CMakeFiles/test-iterators2_cpp20.dir/src/unit-iterators2.cpp.o -MF CMakeFiles/test-iterators2_cpp20.dir/src/unit-iterators2.cpp.o.d -o CMakeFiles/test-iterators2_cpp20.dir/src/unit-iterators2.cpp.o -c /work2/00434/eijkhout/json/json-3.12.0/tests/src/unit-iterators2.cpp
"/usr/lib/gcc/x86_64-redhat-linux/11/../../../../include/c++/11/ranges", line 1753: error: a constexpr function cannot have a nonliteral return type "std::__success_type<nlohmann::json_abi_v3_12_0::detail::iteration_proxy_value<nlohmann::json_abi_v3_12_0::detail::iter_impl<nlohmann::json_abi_v3_12_0::basic_json<std::map, std::vector, std::string, bool, int64_t, uint64_t, double, std::allocator, nlohmann::json_abi_v3_12_0::adl_serializer, std::vector<uint8_t, std::allocator<uint8_t>>, void>>>::string_type>::type" (aka "std::string")
          {
          ^
          detected during instantiation of class "std::ranges::transform_view<_Vp, _Fp>::_Iterator<_Const> [with _Vp=std::ranges::subrange<nlohmann::json_abi_v3_12_0::detail::iteration_proxy_value<nlohmann::json_abi_v3_12_0::detail::iter_impl<nlohmann::json_abi_v3_12_0::basic_json<std::map, std::vector, std::string, bool, int64_t, uint64_t, double, std::allocator, nlohmann::json_abi_v3_12_0::adl_serializer, std::vector<uint8_t, std::allocator<uint8_t>>, void>>>, nlohmann::json_abi_v3_12_0::detail::iteration_proxy_value<nlohmann::json_abi_v3_12_0::detail::iter_impl<nlohmann::json_abi_v3_12_0::basic_json<std::map, std::vector, std::string, bool, int64_t, uint64_t, double, std::allocator, nlohmann::json_abi_v3_12_0::adl_serializer, std::vector<uint8_t, std::allocator<uint8_t>>, void>>>, std::ranges::subrange_kind::unsized>, _Fp=lambda [](const auto &)->auto, _Const=false]" at line 963 of "/work2/00434/eijkhout/json/json-3.12.0/tests/src/unit-iterators2.cpp"

[nlohmann]

We recently fixed a related-but-different JSON_HAS_RANGES issue: nvcc (CUDA Toolkit) 12.0.x/12.1.x specifically choked on the enable_borrowed_range variable-template syntax in iteration_proxy.hpp (fixed in PR #5248, now on develop). That fix does not cover this case, though -- nvc++ (NVIDIA HPC SDK, the "nvidia 25.3" in your title) is a different compiler from nvcc and isn't affected by that guard. As a workaround, building with -DJSON_HAS_RANGES=0 should still resolve the failure. If you can confirm that works, it'd be worth filing a separate, dedicated report for an nvc++-specific JSON_HAS_RANGES exclusion, mirroring the nvcc one -- we don't currently have one tracked for nvc++.

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This reply was drafted by Claude Code on behalf of @nlohmann, as part of a review of open discussions.

[VictorEijkhout]

Your reply was confusing / incomplete:

"building with -DJSON_HAS_RANGES=0"

should have been: add a cmake flag

-D CMAKE_CXX_FLAGS='-DJSON_HAS_RANGES=0'

Next time reply from a human please? This word soup was hard to parse.

[nlohmann]

That's the spirit!

[nlohmann]

Thanks for confirming that -D CMAKE_CXX_FLAGS='-DJSON_HAS_RANGES=0' works.

The compile error comes from one of the library's tests, not from the library itself. With libstdc++ 11, nvc++ rejects a std::views::transform lambda in unit-iterators2.cpp that returns a std::string by value. We fixed that test in #4744, a few days after 3.12.0 came out. Our CI builds and runs the test suite with nvc++ 25.5 on top of libstdc++ 11, with ranges support on, and it passes. The next release should build without the flag.

If you call std::views::transform in your own code with this compiler and standard library, have the lambda return a std::string_view or a reference rather than a std::string by value.

If the current develop branch still fails for you with nvc++ 25.3, please let us know.

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Written by Claude Code on behalf of @nlohmann.

[VictorEijkhout]

Confirm: the dev branch compiles without that flag.