p4c: Build errors with Protobuf 23

Hey,

I recently created a package of the p4 compiler for the Arch Linux User Repository: https://aur.archlinux.org/packages/p4lang-p4c It was already a bit complicated to build it, but I eventually got it working by using CMAKE_UNITY_BUILD=ON (for some reason the compilation error-ed without it) and by specifying PROTOBUF_LIBRARY=protobuf, because it would complain about the Protobuf version or not find it while linking (see https://aur.archlinux.org/cgit/aur.git/tree/PKGBUILD?h=p4lang-p4c#n50).

Recently, the Arch Linux developers updated protobuf from 21.12 to 23.3 (don’t ask me about these version numbers, but that seems to correspond to library version 4.23.3, while the previous one was 3.21.12). Anyway, this protobuf version depends on the abseil cpp libraries, and since CMakeLists.txt currently only links against Protobuf directly, this leaves undefined references that cause the build to fail. I found a possible solution to that problem here: https://github.com/protocolbuffers/protobuf/issues/12292#issuecomment-1529680040 By adding CONFIG to the find_package call, CMake should load the respective protobuf cmake files, which would then also link the program correctly against the abseil libraries and other possible dependencies of protobuf.

However, since adding this (and changing the version number from 3.0.0 to 23.3.0, because it complained), the build fails at the Genering protobuf dependencies step with:

[ 47%] Generating protobuf files
/bin/sh: line 1: -I: command not found
make[2]: *** [control-plane/CMakeFiles/controlplane-gen.dir/build.make:78: control-plane/google/rpc/status.pb.cc] Error 127
make[1]: *** [CMakeFiles/Makefile2:1871: control-plane/CMakeFiles/controlplane-gen.dir/all] Error 2
make: *** [Makefile:166: all] Error 2

Running make with -d for debug mode shows the following:

[ 47%] Generating protobuf files
Reaping winning child 0x561bb9b00500 PID 192167 
cd /home/jkhsjdhjs/aur/p4lang-p4c/src/p4lang-p4c/build/control-plane && -I /home/jkhsjdhjs/aur/p4lang-p4c/src/p4lang-p4c/control-plane/p4runtime/proto -I/home/jkhsjdhjs/aur/p4lang-p4c/src/p4lang-p4c/control-plane --cpp_out /home/jkhsjdhjs/aur/p4lang-p4c/src/p4lang-p4c/build/control-plane --python_out /home/jkhsjdhjs/aur/p4lang-p4c/src/p4lang-p4c/build/control-plane /home/jkhsjdhjs/aur/p4lang-p4c/src/p4lang-p4c/control-plane/google/rpc/status.proto /home/jkhsjdhjs/aur/p4lang-p4c/src/p4lang-p4c/control-plane/p4runtime/proto/p4/config/v1/p4info.proto /home/jkhsjdhjs/aur/p4lang-p4c/src/p4lang-p4c/control-plane/p4runtime/proto/p4/config/v1/p4types.proto /home/jkhsjdhjs/aur/p4lang-p4c/src/p4lang-p4c/control-plane/p4runtime/proto/p4/v1/p4runtime.proto /home/jkhsjdhjs/aur/p4lang-p4c/src/p4lang-p4c/control-plane/p4runtime/proto/p4/v1/p4data.proto
Live child 0x561bb9b00500 (control-plane/google/rpc/status.pb.cc) PID 192168 
/bin/sh: line 1: -I: command not found
Reaping losing child 0x561bb9b00500 PID 192168 
make[2]: *** [control-plane/CMakeFiles/controlplane-gen.dir/build.make:78: control-plane/google/rpc/status.pb.cc] Error 127
Removing child 0x561bb9b00500 PID 192168 from chain.
Reaping losing child 0x55a33b04adc0 PID 192166 
make[1]: *** [CMakeFiles/Makefile2:1871: control-plane/CMakeFiles/controlplane-gen.dir/all] Error 2
Removing child 0x55a33b04adc0 PID 192166 from chain.
Reaping losing child 0x55ed0f977d70 PID 192061 
make: *** [Makefile:166: all] Error 2
Removing child 0x55ed0f977d70 PID 192061 from chain.

The third line shows, that the command executed if the cd command succeeds is simply -I, so I assume that some variable containing the path to some executable (maybe the protoc executable), is now no longer defined.

Do you have any idea what might be going wrong here? Thanks in advance!