Fix the compiling error for xcode 10

[JerryShih]

The xcode 10 removes the deprecated libstdc++ library. Now, we should
use libc++ instead.

Here is the error message when I try to build the protobuf with cpp implementation.

warning: include path for stdlibc++ headers not found; pass '-std=libc++' on the command line to use the libc++ standard library instead [-Wstdlibcxx-not-found]
In file included from google/protobuf/pyext/extension_dict.cc:34:
./google/protobuf/pyext/extension_dict.h:39:10: fatal error: 'memory' file not found
#include

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[JerryShih]

I signed it!

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[JerryShih]

@anandolee
Could you please review this change?

[JerryShih]

@TeBoring
How about this change?

[TeBoring]

Do you known since which version of xcode does libc++ exist? We probably can add it by default.

[JerryShih]

@TeBoring
Maybe start from xcode5. What's the minimum requirement to build protobuf at mac? Could I change to libc++ by default?

[TeBoring]

We provide support for up to osx 10.6 for now. It seems xcode 4 can still be run on osx 10.6.
https://stackoverflow.com/questions/13047630/what-is-the-latest-version-of-xcode-i-can-use-on-10-6-8
However, we do cross-compiling. If we don't use libc++, our binary won't work on machines with only xcode10 installed.
So the problem is that it's impossible to have a binary that supports both xcode4 and xcode10. Is that true?

[TeBoring]

https://gitlab.kitware.com/cmake/cmake/issues/18396
https://developer.apple.com/documentation/xcode_release_notes/xcode_10_release_notes

Libgcc is obsoleted. Xcode 10 can no longer build apps with deployment targets of macOS 10.4 and 10.5. (42818150, 38035243)

I feel since xcode10 still claims to support osx10.6, it should not deprecate libstdc++...

[TeBoring]

In https://developer.apple.com/documentation/xcode_release_notes/xcode_10_release_notes, it suggests:

C++ projects must now migrate to libc++ and are recommended to set a deployment target of macOS 10.9 or later, or iOS 7 or later

Perhaps the proper change is to set MACOSX_DEPLOYMENT_TARGET: https://github.com/grpc/grpc/blame/0a1d0d25a2392a0fa70d8ad54c572bdc726b62d3/tools/distrib/python/grpcio_tools/setup.py#L123

[JerryShih]

@TeBoring
It looks like the xcode 4.3 has libc++.
https://stackoverflow.com/questions/9345271/xcode-4-3-and-c11-include-paths/13621792

In https://developer.apple.com/documentation/xcode_release_notes/xcode_10_release_notes, it suggests:

C++ projects must now migrate to libc++ and are recommended to set a deployment target of macOS 10.9 or later, or iOS 7 or later

Perhaps the proper change is to set MACOSX_DEPLOYMENT_TARGET: https://github.com/grpc/grpc/blame/0a1d0d25a2392a0fa70d8ad54c572bdc726b62d3/tools/distrib/python/grpcio_tools/setup.py#L123

I can't catch the idea that we could change MACOSX_DEPLOYMENT_TARGET. You said that the protobuf could run at 10.6. How could we change MACOSX_DEPLOYMENT_TARGET to 10.9?

[TeBoring]

We have to support the newest xcode. For that, we can drop the older version of Mac OS.

…

On Wed, Oct 24, 2018 at 18:13 Jerry ***@***.***> wrote: @TeBoring <https://github.com/TeBoring> It looks like the xcode 4.3 has libc++. https://stackoverflow.com/questions/9345271/xcode-4-3-and-c11-include-paths/13621792 In https://developer.apple.com/documentation/xcode_release_notes/xcode_10_release_notes, it suggests: C++ projects must now migrate to libc++ and are recommended to set a deployment target of macOS 10.9 or later, or iOS 7 or later Perhaps the proper change is to set MACOSX_DEPLOYMENT_TARGET: https://github.com/grpc/grpc/blame/0a1d0d25a2392a0fa70d8ad54c572bdc726b62d3/tools/distrib/python/grpcio_tools/setup.py#L123 I can't catch the idea that we could change MACOSX_DEPLOYMENT_TARGET. You said that the protobuf could run at 10.6. How could we change MACOSX_DEPLOYMENT_TARGET to 10.9? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#5238 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AE9H5aVlay_D4otSY7frn6T5Xugc1BAdks5uoRAcgaJpZM4XNurE> .

[JerryShih]

@TeBoring
So, what should I do for the next step?
We could replace the libstdc++ with libc++. The xcode 4.3 has libc++.
Do you mean I could add "os.environ['MACOSX_DEPLOYMENT_TARGET'] = '10.9'" to setup.py?

[TeBoring]

Yes

…

On Wed, Oct 24, 2018 at 21:52 Jerry ***@***.***> wrote: @TeBoring <https://github.com/TeBoring> So, what should I do for the next step? We could replace the libstdc++ with libc++. The xcode 4.3 has libc++. Do you mean I could add "os.environ['MACOSX_DEPLOYMENT_TARGET'] = '10.9'" to setup.py? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#5238 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AE9H5ePXyLVC6D9YJShuCZoaSB9DKqCCks5uoUOfgaJpZM4XNurE> .

[JerryShih]

@TeBoring
Here is the patch with "os.environ['MACOSX_DEPLOYMENT_TARGET'] = '10.9'" only.
Thank you.

[TeBoring]

Could you do me a favor to send another PR with the same change to python-wheel-dev branch?
I need to run a test on the branch.

[JerryShih]

@TeBoring
Here is the pr for python-wheel-kekoro-dev branch.
#5303

[TeBoring]

Fixed in #5406