Can't build project (either API_ONLY or default options) using CMake from release tarball

[lidavidm]

Describe your environment

Ubuntu 18.04 x86_64, OpenTelemetry v1.0.0-rc2

$ uname -a
Linux partita 5.4.0-74-generic #83~18.04.1-Ubuntu SMP Tue May 11 16:01:00 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
$ cmake --version
cmake version 3.19.6
$ g++ --version
g++ (crosstool-NG 1.24.0.133_b0863d8_dirty) 9.3.0

Steps to reproduce

$ wget https://github.com/open-telemetry/opentelemetry-cpp/archive/refs/tags/v1.0.0-rc2.tar.gz
$ tar xf v1.0.0-rc2.tar.gz
$ cd opentelemetry-cpp-1.0.0-rc2/
$ mkdir build && cd build
$ cmake .. -DWITH_API_ONLY=ON # or omit

What is the expected behavior?

We should be able to configure OpenTelemetry.

What is the actual behavior?

CMake fails because nlohmann-json isn't included in the release tarball:

-- The C compiler identification is GNU 9.3.0
-- The CXX compiler identification is GNU 9.3.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /home/lidavidm/miniconda3/envs/arrow4/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /home/lidavidm/miniconda3/envs/arrow4/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Building for architecture ARCH=x64
-- Looking for pthread.h
-- Looking for pthread.h - found
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Failed
-- Looking for pthread_create in pthreads
-- Looking for pthread_create in pthreads - not found
-- Looking for pthread_create in pthread
-- Looking for pthread_create in pthread - found
-- Found Threads: TRUE  
Using local nlohmann::json from submodule
CMake Error at CMakeLists.txt:241 (add_subdirectory):
  The source directory

    /home/lidavidm/Code/upstream/arrow-otel2/build/temp/opentelemetry-cpp-1.0.0-rc2/third_party/nlohmann-json

  does not contain a CMakeLists.txt file.


-- Found GTest: /home/lidavidm/miniconda3/envs/arrow4/lib/libgtest.so  
GTEST_INCLUDE_DIRS   = /home/lidavidm/miniconda3/envs/arrow4/include
GTEST_BOTH_LIBRARIES = /home/lidavidm/miniconda3/envs/arrow4/lib/libgtest.so;/home/lidavidm/miniconda3/envs/arrow4/lib/libgtest_main.so
Building with nostd types...
-- Configuring incomplete, errors occurred!
See also "/home/lidavidm/Code/upstream/arrow-otel2/build/temp/opentelemetry-cpp-1.0.0-rc2/build/CMakeFiles/CMakeOutput.log".
See also "/home/lidavidm/Code/upstream/arrow-otel2/build/temp/opentelemetry-cpp-1.0.0-rc2/build/CMakeFiles/CMakeError.log".

Additional context

Ideally, we would just not build components that require nlohmann::json when it's not available, but otherwise, we should at least include it in the release tarball. And at the very least, WITH_API_ONLY should not require this dependency.

We specifically use the release tarball so we can also easily mirror it or provide it offline for a CMake ExternalProject build, instead of using a Git clone which would require Internet connectivity.

[lalitb]

Thanks for reporting @lidavidm. This was discussed earlier here #865 (comment) and should be fixed. cc @maxgolov

[lidavidm]

Ah, sorry for the duplicate, and thanks for pointing me there.

I do see a suggestion to always clone recursively - in that case it might be worth manually uploading release tarballs with submodules included? Since the default GitHub ones do not include them.