Failed to build with external abseil-cpp

[hcoona]

It's simple to understand so I didn't follow the template.

The opentelemetry-cpp vendor parts of the absl source code within the API but without change the namespace. If I build a cpp target included both opentelementry-cpp & abseil-cpp, it would occurred an error (build with bazel & llvm-13):

external/com_google_absl/absl/meta/type_traits.h:162:8: error: redefinition of 'is_detected_convertible_impl<typename std::enable_if<std::is_convertible<Op<Args...>, To>::value>::type, To, Op, Args...>'
struct is_detected_convertible_impl<
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
bazel-out/k8-fastbuild/bin/external/io_opentelemetry_cpp/api/_virtual_includes/api/opentelemetry/nostd/./absl/types/../types/internal/../../meta/type_traits.h:154:8: note: previous definition is here
struct is_detected_convertible_impl<
       ^

The critical rule is to use an alternative namespace than the original namespace absl when vendoring any source code.

[hcoona]

Still failing after add --copt -DHAVE_ABSEIL=1 to .bazelrc

In file included from external/io_opentelemetry_cpp/exporters/ostream/test/ostream_span_test.cc:17:
In file included from external/com_google_googletest/googletest/include/gtest/gtest.h:62:
In file included from external/com_google_googletest/googletest/include/gtest/internal/gtest-internal.h:40:
In file included from external/com_google_googletest/googletest/include/gtest/internal/gtest-port.h:2299:
In file included from external/com_google_absl/absl/types/any.h:57:
In file included from external/com_google_absl/absl/utility/utility.h:49:
In file included from external/com_google_absl/absl/base/internal/inline_variable.h:20:
external/com_google_absl/absl/base/internal/identity.h:26:8: error: redefinition of 'identity'
struct identity {
       ^
bazel-out/k8-fastbuild/bin/external/io_opentelemetry_cpp/api/_virtual_includes/api/opentelemetry/nostd/absl/types/../types/internal/../../base/internal/identity.h:26:8: note: previous definition is here
struct identity {
       ^

[lalitb]

Does change the order of inclusion of header file helps as documented here: https://github.com/open-telemetry/opentelemetry-cpp/blob/main/examples/otlp/README.md#additional-notes-regarding-abseil-library

If not, please let us know the version of abseil-cpp used externally?

[hcoona]

I didn't try changing the order. It's ridiculous to make it work relying about including order, and our coding guideline disallow manually ordering the includes.

The abseil-cpp commit id is 3c8b5d7 from master branch.

[lalitb]

Agree, I still believe -DHAVE_ABSEIL=ON should work in this case. If not, this needs to be fixed.

[lalitb]

Tested with below cmake command, and the build and tests were successful:

$ cmake -DWITH_ABSEIL=ON -DCMAKE_PREFIX_PATH=/home/labhas/custom_abseil/ .. && make -j14

Looks like the problem is specific to bazel. Need to test more.

[owent]

We meet the same problem and I solve this problem by add modify HAVE_ABSEIL to api/BUILD and the move the paths of internal abseil-cpp.
This issue can assign to me and I can try to merge the changes here and add some tests some days later. @lalitb

[lalitb]

Thanks, @owent. Assigned to you.