POC fix for GCC/Clang under Linux for header only singletons

[astitcher]

Changes

This the minimal change that will work for GCC with Linux. This approach
won't work for Windows. MacOS is unknown but might work.

Fixes #1520

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
  • This is a very small perhaps trivial change
• Unit tests have been added
• Changes in public API reviewed
  • No changes to public API

[astitcher]

I have created this PR because this is the patch that is going to be used by the Fedora/RHEL rpm packages until this issue is resolved in an official release of opentelemetry-cpp.

I think this is a fine approach for Linux etc. and it is about the minimal change I could find. I'm completely fine with this not being merged though if there is a better approach that might work for Windows/Visual Studio too.

[codecov]

Codecov Report

Merging #1594 (e593a9c) into main (22e64e2) will increase coverage by 0.05%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1594      +/-   ##
==========================================
+ Coverage   84.96%   85.00%   +0.05%     
==========================================
  Files         156      156              
  Lines        4977     4977              
==========================================
+ Hits         4228     4230       +2     
+ Misses        749      747       -2     

Impacted Files	Coverage Δ
api/include/opentelemetry/baggage/baggage.h	97.33% <100.00%> (ø)
...ntelemetry/context/propagation/global_propagator.h	100.00% <100.00%> (ø)
...pi/include/opentelemetry/context/runtime_context.h	97.60% <100.00%> (ø)
api/include/opentelemetry/metrics/provider.h	100.00% <100.00%> (ø)
api/include/opentelemetry/trace/provider.h	100.00% <100.00%> (ø)
api/include/opentelemetry/trace/trace_state.h	97.60% <100.00%> (ø)
sdk/src/trace/batch_span_processor.cc	90.63% <0.00%> (-0.78%)	⬇️
...dk/include/opentelemetry/sdk/metrics/instruments.h	0.00% <0.00%> (ø)
ext/src/http/client/curl/http_client_curl.cc	81.44% <0.00%> (+1.14%)	⬆️

[owent]

Is this duplicated of #1595 ?

[marcalff]

PR #1595 tests the api fix from this branch, with unit tests implemented by PR #1525

In general, the fix works for gcc and clang, with the exception of a crash seen when using the STL.

See CI / CMake C++20 test

Update:

the fix works with gcc and clang, verified by the unit test.
The WITH_STL segfault was a makefile bug, fixed in PR#1595

[astitcher]

@marcalff Thank you for #1595. should I close this PR in favor of that one?

[marcalff]

@marcalff Thank you for #1595. should I close this PR in favor of that one?

@astitcher ,

Thanks for also testing on your side.

The change for gcc and clang is the similar in PR#1595 and here, with added unit tests in 1595,
so yes, I don't see the need to keep this PR open.

PR#1595 contains more code for windows, but if this can not be made to work I will cleanup the extra ifdef when merging, so it will look like this PR here if only the gcc/clang fix is merged.

[astitcher]

Closing this in favor of #1595