Build googletest at buildtime, relying on CMake

[santiagorr]

I believe it would be great to better integrate googletest into the opentelemetry-cpp's build process, so when distro/system-wide googletest source code is available, it can be built along with opentelemetry-cpp.

As googletest upstream recommends, gtest and gmock should be compiled with the same flags than the tested code (http://groups.google.com/group/googletestframework/browse_thread/thread/668eff1cebf5309d). Upstream doesn't recommend to rely on precompiled libraries.

I found a related issue while packaging opentelemetry-cpp to debian, getting tests that end up with FATAL, even if they should pass. E.g.:

test 515
        Start 515: exporter.otlp.OtlpHttpExporterTest.Shutdown

515: Test command: /home/santiago/cpp/opentelemetry-cpp-1.19.0/obj-x86_64-linux-gnu/exporters/otlp/otlp_http_exporter_test "--gtest_filter=OtlpHttpExporterTest.Shutdown"
515: Working Directory: /home/santiago/cpp/opentelemetry-cpp-1.19.0/obj-x86_64-linux-gnu/exporters/otlp
515: Test timeout computed to be: 1500
515: Running main() from ./googletest/src/gtest_main.cc
515: Note: Google Test filter = OtlpHttpExporterTest.Shutdown
515: [==========] Running 1 test from 1 test suite.
515: [----------] Global test environment set-up.
515: [----------] 1 test from OtlpHttpExporterTest
515: [ RUN      ] OtlpHttpExporterTest.Shutdown
515: [Error] File: ./exporters/otlp/src/otlp_http_exporter.cc:150 [OTLP TRACE HTTP Exporter] ERROR: Export 0 trace span(s) failed, exporter is shutdown
515: [       OK ] OtlpHttpExporterTest.Shutdown (0 ms)
515: [----------] 1 test from OtlpHttpExporterTest (0 ms total)
515: 
515: [----------] Global test environment tear-down
515: [==========] 1 test from 1 test suite ran. (0 ms total)
515: [  PASSED  ] 1 test.
515: 
515: [ FATAL ] ./googletest/include/gtest/internal/gtest-port.h:1811:: pthread_key_delete(key_)failed with error 22
515/609 Test #515: exporter.otlp.OtlpHttpExporterTest.Shutdown ..........................................................Subprocess aborted***Exception:   0.01 sec
Running main() from ./googletest/src/gtest_main.cc
Note: Google Test filter = OtlpHttpExporterTest.Shutdown
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from OtlpHttpExporterTest
[ RUN      ] OtlpHttpExporterTest.Shutdown
[Error] File: ./exporters/otlp/src/otlp_http_exporter.cc:150 [OTLP TRACE HTTP Exporter] ERROR: Export 0 trace span(s) failed, exporter is shutdown
[       OK ] OtlpHttpExporterTest.Shutdown (0 ms)
[----------] 1 test from OtlpHttpExporterTest (0 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test suite ran. (0 ms total)
[  PASSED  ] 1 test.

[ FATAL ] ./googletest/include/gtest/internal/gtest-port.h:1811:: pthread_key_delete(key_)failed with error 22

I understand that for opentelemetry-cpp's CI, googletest is setup with ./ci/setup_googletest.sh, but it is suboptimal from a distro packaging PoV.

I'd propose to rely on CMake's very features (ExternalProject / FindGTest) to build and find the googletest libraries. I belive

[lalitb]

@santiagorr Thanks for the issue. Would you like to contribute the PR?

[santiagorr]

@santiagorr Thanks for the issue. Would you like to contribute the PR?

I am far from being a cmake expert. I could try, if nobody else is eager to address it, but it would be great if someone with more cmake experience is available.

Thanks for the 'triage/accepted' label!

[ThomsonTan]

Thanks for raising the issue, @santiagorr.

We have googletest as submodule under https://github.com/open-telemetry/opentelemetry-cpp/tree/main/third_party.

Would that be very different than the ExternalProject / FindGTest approach?

[sjinks]

Would that be very different than the ExternalProject / FindGTest approach?

No. This is one of the approaches recommended by Google:

Add GoogleTest as a git submodule or equivalent. This may not always be possible or appropriate. Git submodules, for example, have their own set of advantages and drawbacks.