CMake generation requiring generated files

Question

I'm building a project using CMake in multiple subdirectories. There is a parent directory containing a parent CMakeLists file, and each subdirectory contains its own CMakeLists file. As such, I'm using the add_subdirectory command to run the subdirectories.

My issue is that one of the subdirectories generates code that another subdirectory needs in order to build. Specifically, it's Google Protocol Buffers. The CMakeLists file in that subdirectory will generate the pb.cc and pb.h files if run independently, but until I do so, I cannot generate the cache of the parent CMake file as it complains it's missing those source files.

Directory structure is as follows:

/
--CMakeLists.txt
--protobuf/
----CMakeLists.txt
----src/
--main/
----CMakeLists.txt
----src/

Where the main subdirectory requires files generated by the protobuf subdirectory.

Is there a way I can have the parent CMakeLists file build the subdirectory as part of its generation step? Or somehow mark the protobuf files as required, but missing, so the generation does not fail?

Teivaz Teivaz · Accepted Answer · 2019-08-09T22:37:45

You can try running this particular cmake file as execute_process before including the main file. But this goes against the designed cmake usage.

The correct answer would be to make your generation step a part of build process. If you can post a minimal, reproducible example of your problem I could give you concrete ways to solve your problem directly instead of making your workaround work.

CMake generation requiring generated files

1 Answers