tools can only be built with appropriate nlohmann_json version

[tmadlener]

#163 introduced a CI failure, because it tries to build a target that links to nlohmann_json, which is not explicitly discovered via find_package before (or at least not with an appropriate version).

This should be rather easy to fix by putting the find_package that is currently in tests into a CMakeLists.txt further up the directory tree and then dealing with it appropriately.

[vvolkl]

I'd prefer to add a cmake option and always build the nlohmann_json dependent parts except if this is explicitly turned off.

[tmadlener]

Yeah, probably the solution that is easier to maintain.

[zaborowska]

On that topic... EDM4hep that I build locally works well with nlohmann_json 3.11.2, but it fails when 3.10.2 was used. Are you sure that 3.10 is the minimal requirement? That's the error I get:

[ 29%] Building CXX object edm4hep/CMakeFiles/edm4hep.dir/src/ParticleID.cc.o
/builds/azaborow/OpenDataDetector/EDM4hep/edm4hep/src/ParticleID.cc: In function 'void edm4hep::to_json(nlohmann::json&, const edm4hep::ParticleID&)':
/builds/azaborow/OpenDataDetector/EDM4hep/edm4hep/src/ParticleID.cc:138:3: error: no matching function for call to 'nlohmann::basic_json<>::basic_json(<brace-enclosed initializer list>)'
  138 |   };
      |   ^
In file included from /builds/azaborow/OpenDataDetector/EDM4hep/edm4hep/edm4hep/ParticleID.h:15,
                 from /builds/azaborow/OpenDataDetector/EDM4hep/edm4hep/src/ParticleID.cc:4:
/usr/local/include/nlohmann/json.hpp:19687:5: note: candidate: 'nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType>::basic_json(nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType>&&) [with ObjectType = std::map; ArrayType = std::vector; StringType = std::__cxx11::basic_string<char>; BooleanType = bool; NumberIntegerType = long int; NumberUnsignedType = long unsigned int; NumberFloatType = double; AllocatorType = std::allocator; JSONSerializer = nlohmann::adl_serializer; BinaryType = std::vector<unsigned char>]'
19687 |     basic_json(basic_json&& other) noexcept
      |     ^~~~~~~~~~
/usr/local/include/nlohmann/json.hpp:19687:5: note:   candidate expects 1 argument, 5 provided
[...]

Moreover, I have trouble updating nlohmann_json version because it seems to be always using the version ROOT was compiled with (but maybe that compatibility is needed).

[tmadlener]

I am not sure I have ever tried with 3.10.2, but it looks like it is not sufficient. The lowest I have tried is 3.10.5.

I am not sure which version of nlohmman_json takes precedence if root was compiled with a different one (also probably depending on whether root was built with builtin_nlohmannjson or whether root also uses an external installation.

Which stack have you tried to build against? I will have another look and see whether we have to tighten that requirement.

On a side note: I think the main problem this issue tried to keep track of has been solved with #185

[zaborowska]

I was using this docker image, it's used in the CI of the Open Data Detector.

ROOT uses external installation (v 3.10.2).

[tmadlener]

Thanks for testing. Do you need the JSON output capabilities, or would it be enough to simply make the requirements higher, so that no JSON output is built?

[zaborowska]

I think it would make sense to have the requirement changed to 3.10.5, since it's clearly not sufficient to have 3.10.

I do not need JSON output, so it was just an obstacle in the installation for me. But I just upgraded the docker image and we use now 3.10.5, so I do not have any problem anymore.