Prefer using system Abseil if available

[carlocab]

Newer versions of Protobuf (22+) pull in Abseil as a dependency. We
want to avoid using our bundled copy for these cases, as this will
likely conflict with the version of Abseil that Protobuf uses.

The simplest way to do this seems to be to just prefer a system
installation of Abseil if it's available.

I've also cherry-picked from #207 to simplify what I want to do here.

[carlocab]

I've also noticed some similar logic gated behind if(UNIX OR MINGW), but I don't quite follow why this is done. Happy to require something similar behind using a system Abseil if desired.

[carlocab]

Ping @haberman?

[haberman]

Sorry for the long delay on this.

The CI tests aren't running on this PR and I'm not sure why. They seems to be running on some PRs but not others.

The tests ran on the most recently merged PR #370. I wonder if there is any chance that PR broke the CI. Any idea @arunsathiya?

[arunsathiya]

The tests ran on the most recently merged PR #370. I wonder if there is any chance that PR broke the CI. Any idea @arunsathiya?

I am not sure just yet, but the workflows on the PR #370 were manually triggered by you, as a maintainer of the project.

cifuzz.yml	build.yml

Would something similar be required here? I am unable to see those workflows on the checks section of the current PR #347, possibly because I am not a maintainer of this project:

[haberman]

I saw the button on the other PR and clicked it. But I don't see the button here. I am not sure why it disappeared.

[carlocab]

I rebased on main. I think you can run the tests now.

[carlocab]

The external Abseil build seems to choke at trying to build googletest. I've fixed that by pointing it at third_party/googletest.

[carlocab]

The external Abseil build seems to choke at trying to build googletest. I've fixed that by pointing it at third_party/googletest.

Oops, that didn't work for some reason. I've just disabled Abseil's tests.

[carlocab]

Ping @haberman?

If it helps, we've been using a version of this patch at Homebrew for over a year now¹, and haven't gotten any complaints about it. (We've had at least ~5,000 installs in the past year.² This count excludes users who opt out of Homebrew analytics.)

Footnotes

1. https://github.com/Homebrew/homebrew-core/commit/be131c6c8ea3744a39d7fe059d2fb53cae464fc6 ↩

2. https://formulae.brew.sh/formula/bloaty#default ↩

[haberman]

Unfortunately I think I need to roll this back for now, as it broke the continuous build: https://github.com/google/bloaty/actions/runs/10566910014/job/29274712202#step:10:315

/home/runner/work/bloaty/bloaty/bloaty/third_party/abseil-cpp/absl/debugging/failure_signal_handler.cc:139:32: error: no matching function for call to ‘max(long int, int)’
139 | size_t stack_size = (std::max(SIGSTKSZ, 65536) + page_mask) & ~page_mask;

We may need to update the version of ABSL first.

[haberman]

Alternatively, would you be interested in trying to fix the continuous build with a fix-forward?

[carlocab]

Alternatively, would you be interested in trying to fix the continuous build with a fix-forward?

Sure, let me look at trying to update the bundled copy of abseil.

[carlocab]

#384