Add JSON C++ support - Bazel

[jajanet]

PR to import JSON in C++ as an external dependency. Would be useful for zPages/TraceZ and other SDK features for OpenTelemetry. @maxgolov

Reference: nlohmann/json#1606

[maxgolov]

I assume this is for Bazel only right now. There are two approaches for CMake:

• vcpkg install nlohmann-json - safe; OR
• add it as submodule to third_party - I don't think we agreed yet we can use submodules.

[pyohannes]

add it as submodule to third_party - I don't think we agreed yet we can use submodules.

I think this would be necessary to make it work cross-platform. There were some discussions about vendoring strategies with CMake/Bazel, but no final conclusions were made.

There's also the option to just vendor the single include version. It almost feels like a bit of an overkill to add a submodule if all we need is just a single header.

[pyohannes]

This is still marked as a draft. Is it intended to solve all the TODOs mentioned in this PR?

[jajanet]

I think we could leave it as is, and merge. @maxgolov said he can handle adding CMake support.

Alternatively, different features could also add JSON C++ via CMake by adding it manually to their CMake file:

find_package(nlohmann_json 3.2.0 REQUIRED)
...
add_library(foo ...)
...
target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)

[pyohannes]

I think we could leave it as is, and merge. @maxgolov said he can handle adding CMake support.

Ok. Can you please write issues for TODOs that remain open after merging this PR?

[jajanet]

Will do, thank you!