[Bug]: Problem using abseil on Macos with C++14 only.

[KerstinKeller]

Describe the issue

Our eCAL project is using github actions to do CI.
With the newest available MacOS Tag (20230516.1), using abseil https://ghcr.io/v2/homebrew/core/abseil/manifests/20230125.3-1 and protobuf https://ghcr.io/v2/homebrew/core/protobuf/manifests/23.3 (e.g. most recent release)
we cannot use protobuf in our project anymore, as it leads to build problems:

In file included from /Users/runner/work/ecal/ecal/contrib/ecalproto/src/ecal_proto_decoder.cpp:24:
In file included from /Users/runner/work/ecal/ecal/contrib/ecalproto/include/ecal/protobuf/ecal_proto_decoder.h:29:
In file included from /usr/local/include/google/protobuf/message.h:119:
In file included from /usr/local/include/google/protobuf/arena.h:54:
In file included from /usr/local/include/google/protobuf/port.h:50:
In file included from /usr/local/include/absl/types/optional.h:39:
/usr/local/include/absl/utility/utility.h:164:12: error: no member named 'in_place_t' in namespace 'std'
using std::in_place_t;
      ~~~~~^

Now the question is: I though that to use the abseil library, one only needs to have C++14? However as std::in_place_t is C++17, I guess otherwise?
Or do we need to enable C++17 compile features, if the compiler supports it?

Steps to reproduce the problem

See the following eCAL build https://github.com/eclipse-ecal/ecal/actions/runs/5357089900/jobs/9717467948

What version of Abseil are you using?

20230125.3-1

What operating system and version are you using?

Macos 12

What compiler and version are you using?

AppleClang 14.0.0.14000029

What build system are you using?

CMake

Additional context

It's a bit unclear to me, wether this is an abseil issue, a protobuf issue, or in the end a CMake issue.
Our build activates only the C++14 standard, and we assume that the dependencies support this, as well.

From my understanding, if the C++17 flags are not passed to the compiler, I should be able to use the abseil library in C++14 "mode"? Or is this rather tied to the compiler, and its capabilities?

[derekmauro]

We do not maintain the homebrew package. From a quick Google search it looks like this is the recipe https://github.com/Homebrew/homebrew-core/blob/master/Formula/abseil.rb, and it is forcing C++17 on its users. We can't help you with this.

[JLP04]

Maybe open a ticket on homebrew/homebrew-core