error: expected initializer before ‘<’ token

[pipelinedestroyer]

Description

When using the single include header (https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json.hpp) I get the following error during compilation
error: expected initializer before ‘<’ token
in line 5323.
Sorry if it's an easy fix, I don't have much experience with C++.
I'm using g++ together with the latest CUDA compiler nvcc under WSL.
Edit: does not work using C++20, C++17 (probably below as well) compiles flawlessly

Reproduction steps

Include "json.hpp" in any header file

Expected vs. actual results

Expected: Successful compilation
Actual: No compilation

Minimal code example

No response

Error messages

No response

Compiler and operating system

g++ (Ubuntu 12.1.0-2ubuntu1~22.04) 12.1.0 | Cuda compilation tools, release 12.0, V12.0.76 Build cuda_12.0.r12.0/compiler.31968024_0

Library version

version 3.11.2

Validation

• The bug also occurs if the latest version from the develop branch is used.
• I can successfully compile and run the unit tests.

Can confirm the bug for

• Ubuntu 22.04
• g++12
• cuda 12
• CMake 3.25.2

build-debug/_deps/json-src/include/nlohmann/detail/iterators/iteration_proxy.hpp:241:22: error: expected initializer before ‘<’ token
  241 |     inline constexpr bool ::std::ranges::enable_borrowed_range<::nlohmann::detail::iteration_proxy<IteratorType>> = true;

No error when the library is compiled with c++17

[shaoyaoqian]

Same error. You might compile the program with nvcc as the default compiler. I have the same problem but can't find the solution. I used the 3.8.0 to avoid this problem.

[steef435]

Looking at this, it seems that support for ranges (a C++20 feature) is disabled on g++11. I have the issue above with nvcc12 and g++10.2.1. Maybe there should be more checks here? (I thought nvcc just used gcc's headers, so maybe it has nothing to do with CUDA/nvcc.)

In any case, I wanted to share the workaround of disabling ranges with

#define JSON_HAS_RANGES 0

before including the library.

[franzpoeschel]

Problem persists in library version 3.12.0

[nlohmann]

Can you please try with the latest develop branch?

[franzpoeschel]

Yep, the error also occurs on the development branch (commit ac0133e):

.../include/nlohmann/detail/iterators/iteration_proxy.hpp:234:22: error: expected initializer before '<' token
  234 |     inline constexpr bool ::std::ranges::enable_borrowed_range<::nlohmann::detail::iteration_proxy<IteratorType>> = true;
      |                      ^

Compilers are:

-- The CXX compiler identification is GNU 10.5.0                                                                                                            
-- The C compiler identification is GNU 10.5.0  
-- The CUDA compiler identification is NVIDIA 12.0.140                                                                                                      

And the error was triggered by an NVCC call

[nlohmann]

Can you copy from the CMake output the snippet which C++ Standard Library is used?

[franzpoeschel]

I do not see that in the CMake output, but the binary is linked to the libstdc++ shipped by gcc:

> ldd picongpu 
        linux-vdso.so.1 (0x00007ffff7fc4000)
        libm.so.6 => /nix/store/nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36/lib/libm.so.6 (0x00007ffff7ed7000)
        libboost_program_options.so.1.81.0 => /nix/store/b19xm70h59bz7j8kwgyr67iphsfa26bq-boost-1.81.0/lib/libboost_program_options.so.1.81.0 (0x00007ffff7e69000)
        libmpi.so.40 => /nix/store/81rq99pfpsflr6h42z641lcwzg8zqnlm-openmpi-5.0.6/lib/libmpi.so.40 (0x00007ffff7ab2000)
        libcudart.so.12 => /nix/store/7dzdpnzkypv9ywhg9i5jh9ljxrxdv96s-cuda-merged-12.0/lib/libcudart.so.12 (0x00007ffff7800000)
        libdl.so.2 => /nix/store/nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36/lib/libdl.so.2 (0x00007ffff77fb000)
        librt.so.1 => /nix/store/nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36/lib/librt.so.1 (0x00007ffff77f6000)
        libcurand.so.10 => /nix/store/7dzdpnzkypv9ywhg9i5jh9ljxrxdv96s-cuda-merged-12.0/lib/libcurand.so.10 (0x00007ffff1200000)
        libpthread.so.0 => /nix/store/nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36/lib/libpthread.so.0 (0x00007ffff77f1000)
        libstdc++.so.6 => /nix/store/jnkxcihmlwcpw0y1f5xibsr5ry92y17r-gcc-10.5.0-lib/lib/libstdc++.so.6 (0x00007ffff102f000)
        libgomp.so.1 => /nix/store/jnkxcihmlwcpw0y1f5xibsr5ry92y17r-gcc-10.5.0-lib/lib/libgomp.so.1 (0x00007ffff77b4000)
        libgcc_s.so.1 => /nix/store/jnkxcihmlwcpw0y1f5xibsr5ry92y17r-gcc-10.5.0-lib/lib/libgcc_s.so.1 (0x00007ffff779a000)
        libc.so.6 => /nix/store/nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36/lib/libc.so.6 (0x00007ffff0e36000)
        /nix/store/nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36/lib/ld-linux-x86-64.so.2 => /nix/store/nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36/lib64/ld-linux-x86-64.so.2 (0x00007ffff7fc6000)
        libucc.so.1 => /nix/store/g0i2rphjnk9ncay0na1bhkf4py10h5ka-ucc-1.3.0/lib/libucc.so.1 (0x00007ffff775e000)
        libpsm2.so.2 => /nix/store/d3cnswndnwdc9jszk8kdzfvwm2vhpy6w-libpsm2-12.0.1/lib/libpsm2.so.2 (0x00007ffff76f3000)
        libopen-pal.so.80 => /nix/store/81rq99pfpsflr6h42z641lcwzg8zqnlm-openmpi-5.0.6/lib/libopen-pal.so.80 (0x00007ffff0d01000)
        libfabric.so.1 => /nix/store/dm53cb9h1d6nw8i0c8dc5r50qkiq4s0m-libfabric-1.22.0/lib/libfabric.so.1 (0x00007ffff0968000)
        libucp.so.0 => /nix/store/w50wwqqslz9cwvihnh67rgg7ri2qbqp8-ucx-1.17.0/lib/libucp.so.0 (0x00007ffff07e5000)
        libucm.so.0 => /nix/store/w50wwqqslz9cwvihnh67rgg7ri2qbqp8-ucx-1.17.0/lib/libucm.so.0 (0x00007ffff76d1000)
        libucs.so.0 => /nix/store/w50wwqqslz9cwvihnh67rgg7ri2qbqp8-ucx-1.17.0/lib/libucs.so.0 (0x00007ffff0767000)
        libuct.so.0 => /nix/store/w50wwqqslz9cwvihnh67rgg7ri2qbqp8-ucx-1.17.0/lib/libuct.so.0 (0x00007ffff7683000)
        libevent_core-2.1.so.7 => /nix/store/cqz2b6rs1lcvp00545fff5x7ykgvyl7d-libevent-2.1.12/lib/libevent_core-2.1.so.7 (0x00007ffff072f000)
        libevent_pthreads-2.1.so.7 => /nix/store/cqz2b6rs1lcvp00545fff5x7ykgvyl7d-libevent-2.1.12/lib/libevent_pthreads-2.1.so.7 (0x00007ffff767e000)
        libhwloc.so.15 => /nix/store/51jqliabhgbn1p9xh8krjn5cnx99wcm3-hwloc-2.11.2-lib/lib/libhwloc.so.15 (0x00007ffff06cc000)
        libpmix.so.2 => /nix/store/i8dppq09dy7bcrxbjl93dzf9igz2mb36-pmix-5.0.5/lib/libpmix.so.2 (0x00007ffff0492000)
        libnuma.so.1 => /nix/store/hayj6hcc8508j2yilxdsk1ar74i0qnla-numactl-2.0.18/lib/libnuma.so.1 (0x00007ffff0483000)
        libuuid.so.1 => /nix/store/qmn58s05ay763vzi7vxax0a6kw37gyjq-util-linux-minimal-2.39.4-lib/lib/libuuid.so.1 (0x00007ffff7670000)
        libatomic.so.1 => /nix/store/4gk773fqcsv4fh2rfkhs9bgfih86fdq8-gcc-13.3.0-lib/lib/libatomic.so.1 (0x00007ffff0478000)
        libbfd-2.43.1.so => /nix/store/x4hyx7dfaw8frfqxg7wxwfrwgdax780x-binutils-2.43.1-lib/lib/libbfd-2.43.1.so (0x00007fffefd06000)
        libz.so.1 => /nix/store/l5g2v1jgfyf3j0jp9iv5b79fi8yrwzpp-zlib-1.3.1/lib/libz.so.1 (0x00007fffefce8000)
        libmunge.so.2 => /nix/store/frbbd39ad9dy9gh7l5zd4iszgb8dszj1-munge-0.5.16/lib/libmunge.so.2 (0x00007fffefcda000)
        libsframe.so.1 => /nix/store/x4hyx7dfaw8frfqxg7wxwfrwgdax780x-binutils-2.43.1-lib/lib/libsframe.so.1 (0x00007fffefcd2000)

[nlohmann]

Can you please share how you call CMake or provide a minimal example?

[franzpoeschel]

I saw this issue originally in these CI runs and then reproduced it locally:

https://gitlab.com/hzdr/crp/picongpu/-/jobs/10167591489
https://gitlab.com/hzdr/crp/picongpu/-/jobs/10167591783

I can try setting up a minimal example

[franzpoeschel]

Alright, the reproducer is simple enough:

// reproducer.cpp

#include <nlohmann/json.hpp>

int main(){}

/nix/store/7dzdpnzkypv9ywhg9i5jh9ljxrxdv96s-cuda-merged-12.0/bin/nvcc \
    -forward-unknown-to-host-compiler \
    -ccbin=/nix/store/8ssrd7ngjhzhcp7ijnd05v094hkayh6r-gcc-wrapper-10.5.0/bin/g++ \
    -DCMAKE_BUILD_TYPE=Release \
    -DCMAKE_CXX_COMPILER_ID=GNU \
    -DCMAKE_CXX_COMPILER_VERSION=10.5.0 \
    -DCMAKE_SYSTEM=Linux-5.15.0-140-generic \
    -DCMAKE_SYSTEM_PROCESSOR=x86_64 \
    -DCMAKE_VERSION=3.30.5 \
    -D_FILE_OFFSET_BITS=64 \
    -D_GNU_SOURCE \
    -D_LARGEFILE_SOURCE \
    -D_POSIX_C_SOURCE=200809L \
    -isystem /nix/store/mbk7c881hdqw0jv4bfa6hjqkrl7rdsy2-cuda_nvcc-12.0.140/include \
    -O3 \
    -DNDEBUG \
    -std=c++20 "--generate-code=arch=compute_52,code=[compute_52,sm_52]" \
    --extended-lambda \
    --expt-relaxed-constexpr \
    --display-error-number \
    -MD \
    -x cu \
    -c ./reproducer.cpp \
    -o ./out.a

Outputs:

/nix/store/0nbmqd7s6vfjlqq0p9xcpm7nwy4mnhnh-nlohmann_json-ac0133ea89a8fd730a9cc9649c5226a9995dc3e1/include/nlohmann/detail/iterators/iteration_proxy.hpp:234:22: error: expected initializer before '<' token
  234 |     inline constexpr bool ::std::ranges::enable_borrowed_range<::nlohmann::detail::iteration_proxy<IteratorType>> = true;
      |

(I used Nix for setting up a local environment that would imitate the CI environment where I observed the error, but from the linked CI runs you can see that this probably makes no big difference.)