Remove C++ content from tensorflow/c/c_api_macros.h

[yongtang]

This PR tries to remove C++ conent from tensorflow/c/c_api_macros.h
so that it is possible to include this file from an external plugin
without depending on tensorflow's C++ headers (tensorflow/core/platform/status.h).

The reason for this move is that for external plugins (e.g., file systems plugins)
that utilize C API, it cannot include status.h as otherwise the whole tensorflow's
C++ library will be a dependency. This defeat the purpose of C APi modular plugin.

This PR place C++ content to tensorflow/core/platform/status.h instead so that
everything will still be combined both for C external plugins and C++ plugins.

(Note the C++ inclusion was added in PR #51647.)

Signed-off-by: Yong Tang yong.tang.github@outlook.com

[yongtang]

@mihaimaruseac At the moment upgrade of tensorflow-io's dependency to TF 2.7.0rc0 is not working due to the C++ inclusion. For that it might make sense to include this PR to 2.7 if there is still enough time.

[mihaimaruseac]

Hmm, can you post what the error message is?

These lines got added recently via #51647 (manual import + fix) as Intel needed this for the 2.7 release.

CC @penpornk

[penpornk]

@yongtang The C++ part is wrapped with #ifdef __cplusplus so I think it should be fine with C compilers. Is the error message something like this?

cc: @jbaiocchi

[yongtang]

Thanks @mihaimaruseac @penpornk.

The issue is because of the following:

1. While C++ part is wrapped within #ifdef __cplusplus, c_api_macros.h itself is a header file and can be included by a C++ source file or C source file.
2. However, if a C++ source file include this header, it will invoke the inclusion of "status.h", which, will include almost lots of C++ header files under tensorflow (not just for C headers under tensorflow/c/:

So the issue is not really about C++ itself, but the include of status.h that expands the inclusion of too many header files (and defeat the purpose of a small limited set of C header files):

Below are the included headers within "status.h":

#include "absl/types/optional.h"
#include "tensorflow/core/platform/logging.h"
#include "tensorflow/core/platform/macros.h"
#include "tensorflow/core/platform/stack_frame.h"
#include "tensorflow/core/platform/stringpiece.h"
#include "tensorflow/core/platform/types.h"
#include "tensorflow/core/protobuf/error_codes.pb.h"

[penpornk]

@yongtang Thank you for the explanation! I agree with refactoring them out. However, I don't think platform/status.h is the right place.

Would you mind creating a new file //tensorflow/c/c_api_macros_internal.h? (This will also require updating the dependencies to c_api_macros.h for //tensorflow/c/experimental/stream_executor and //tensorflow/c/experimental/pluggable_profiler.) -- Or I can also do it. Let me know.

[penpornk]

Thank you very much!

[yongtang]

@mihaimaruseac @penpornk wondering if there is any update on this PR?

It would be great if this PR can be part of the 2.7 release as external plugin will be impacted.