Problem building latest master

so I clone the latest master and run cmake with flags :

-Dbuiltin_nlohmannjson=OFF -DPython3_EXECUTABLE=/usr/bin/python3.10 -DCMAKE_CXX_COMPILER=/usr/bin/g++-11 -DCMAKE_C_COMPILER=/usr/bin/gcc-11 -DCMAKE_CXX_STANDARD=17 -Dopengl=ON

and at the end of the build ( 90% ) it crashes with lots of errors regarding nlohmann json

/usr/include/nlohmann/json_fwd.hpp:37:7: error: redeclared with 9 template parameters
   37 | class basic_json;

This is a fresh Ubuntu install with the basic libraries needed to build root installed as per the documentation … what I’m missing ? Note that I added -Dbuiltin_nlohmannjson=OFF to see if this fixed it, but happens both ways


Please check which version of nlohmann/json.hppinstalled on your system.
Only 3.9 or 3.10 can be used with ROOT.
Or try -Dbuiltin_nlohmannjson=ON.

thanks for the heads-up, it’s working now

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