py-protobuf3: install failures for macOS 10.8 through 10.11: compilation error related to PROTOBUF_MAYBE_CONSTEXPR MapFieldBase(ConstantInitialized)

[mascguy (Christopher Nielsen)]

It looks like this port is failing to install for some macOS releases, blocking builds for a fair number of downstream ports:

/usr/bin/clang -Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -pipe -Os -arch x86_64 -isysroot/ -I. -I../src -I/opt/local/Library/Frameworks/Python.framework/Versions/3.9/include/python3.9 -c google/protobuf/pyext/map_container.cc -o build/temp.macosx-10.10-x86_64-3.9/google/protobuf/pyext/map_container.o -Wno-write-strings -Wno-invalid-offsetof -Wno-sign-compare -Wno-unused-variable -std=c++11 -Wno-shorten-64-to-32 -Wno-deprecated-register -stdlib=libc++  -Wno-shorten-64-to-32
In file included from google/protobuf/pyext/map_container.cc:39:
../src/google/protobuf/map_field.h:332:37: error: constexpr constructor never produces a constant expression [-Winvalid-constexpr]
  explicit PROTOBUF_MAYBE_CONSTEXPR MapFieldBase(ConstantInitialized)
                                    ^
../src/google/protobuf/map_field.h:335:9: note: non-literal type 'internal::WrappedMutex' cannot be used in a constant expression
        mutex_(GOOGLE_PROTOBUF_LINKER_INITIALIZED),
        ^
1 error generated.
error: command '/usr/bin/clang' failed with exit code 1
Command failed:  cd "/opt/local/var/macports/build/_opt_bblocal_var_buildworker_ports_build_ports_python_py-protobuf3/py39-protobuf3/work/protobuf-3.14.0/python" && /opt/local/Library/Frameworks/Python.framework/Versions/3.9/bin/python3.9 setup.py --no-user-cfg --cpp_implementation install --prefix=/opt/local/Library/Frameworks/Python.framework/Versions/3.9 --root=/opt/local/var/macports/build/_opt_bblocal_var_buildworker_ports_build_ports_python_py-protobuf3/py39-protobuf3/work/destroot 
Exit code: 1
Error: Failed to destroot py39-protobuf3: command execution failed

Ignore the fact that this port is compiling code during phase destroot, as that's covered by issue:56534.

These specific failures are occurring on macOS 10.8, 10.9, 10.10, and 10.11.

[mascguy (Christopher Nielsen)]

FYI, this port was building successfully across-the-board, until the following change was committed:

    Change #8856
    Category 	None
    Changed by 	Marius Schamschula <mps@macports.org>
    Changed at 	Fri 04 Dec 2020 01:09:14
    Repository 	https://github.com/macports/macports-ports
    Project 	macports/macports-ports
    Branch 	master
    Revision 	4a9aebc831732ecbf83188cec3c06d05ff822f14
    Comments

    protobuf3-cpp, py-protobuf3: update to 3.14.0

    mosh, protobuf-c: rev bump

    Changed files
        devel/protobuf-c/Portfile
        devel/protobuf3-cpp/Portfile
        net/mosh/Portfile
        python/py-protobuf3/Portfile

[mascguy (Christopher Nielsen)]

Perhaps this ticket should be assigned to Marius...?

[Schamschula (Marius Schamschula)]

So I update a port to the current upstream release version, which builds correctly on my build machine (Mojave). I push the update, only to find out later that El Capitan and below have an issue.

If you want to run older macOS versions, you are likely to run into this type of issue. Upstream developers, in this case Google, often only support the latest OS versions, breaking backwards compatibility.

Making things work on older systems takes a bit of detective work, which requires access to a machine running the older OS. I don't have a machine running anything below Mojave. The only possible way for me to test on older systems is to blindly throw possible fixes at the CI systems.

Of course we're also running into the opposite problem: very old packages need a lot of updates to run on new systems, e.g. the arm64 platform.

[mascguy (Christopher Nielsen)]

KenC and I - among other folks - are running a suite of macOS VMs, from 10.6 through present. Parallels 16 runs them all beautifully, and only requires a one-time $50 purchase.

[mascguy (Christopher Nielsen)]

If you're willing to take a look at this ASAP, and propose some fixes, I'm willing to assist with testing on 10.8 through 10.11.

[Schamschula (Marius Schamschula)]

I'm aware of being able to run VMs (and have installers all the way back to Snow Leopard Server). I have done so in the past. I don't have time and energy to do so.

[Schamschula (Marius Schamschula)]

I just think this is a bad idea to ask anyone revbumping dependent ports to check if they build on 11 macOS versions (12 counting arm64 Big Sur), and fix everything while they're at it.

I'm thinking of updates to ghostscript, for example. Things are often broken before the revbump.

[Schamschula (Marius Schamschula)]

Yes, Ken has been most helpful for a long time in insuring that things work on older systems.

[mascguy (Christopher Nielsen)]

In the near-term, I'm offering to assist with testing on these older macOS releases. Can you propose some fixes?

[Schamschula (Marius Schamschula)]

This issue has been reported upstream ​https://github.com/protocolbuffers/protobuf/issues/8150

[Schamschula (Marius Schamschula)]

See ​https://trac.macports.org/ticket/61751 for a possible solution.

[mascguy (Christopher Nielsen)]

Yes, I was going to suggest blacklisting clang versions older than 9, and/or updating the c++ requirements to 2014.

[Schamschula (Marius Schamschula)]

GitHub PR: ​https://github.com/macports/macports-ports/pull/9822

[Schamschula (Marius Schamschula)]

In f714e0715c4368da1fab8dcf09e77c1a51e529fb/macports-ports (master):

py-protobuf3: Fix build on 10.11 (and below)

Closes: #62158
See: #61751