Recommendation for zephyr project setup with multiple libraries

[thorsten-klein]

I'm relatively new to Zephyr and currently exploring the best project setup for our needs. Our previous project was structured using CMake, with multiple folders and CMakeLists.txt files, each containing add_library(mylib INTERFACE) or add_library(mylib STATIC) statements. Here's an example of our structure:

   ├── CMakeLists.txt
   ├── lib1
   │   ├── CMakeLists.txt
   │   ├── include
   │   └── src
   │       ├── bar.cpp
   │       └── foo.cpp
   ├── lib2
   │   ├── CMakeLists.txt
   │   ├── include
   │   └── src
   │       └── baz.cpp
   └── lib3
       ├── CMakeLists.txt
       ├── include
       └── src
           └── lib.cpp

We use libraries to organize our software into smaller, manageable parts, which are then provided to users for linking to their applications. Each library has a limited scope, containing only the necessary compile definitions and include directories.

As we transition to Zephyr, we aim to maintain this modular structure. We want users to include our software as a single Zephyr module composed of multiple libraries. Technically, using zephyr_library_named to create static libraries that users can link to their applications seems feasible. In contrast to this, combining everything into one library results in an overly complex compile_commands.json file, with unnecessary flags for each compilation unit.

We've started creating a sample app using zephyr_library_named in its CMakeLists.txt. Unfortunately, we encounter warnings such as:

Make Warning at /home/user/work/GIT/zephyrproject/zephyr/cmake/modules/extensions.cmake:593 (message):
 zephyr_library() or zephyr_library_named() called in Zephyr CMake
 application mode.  `library.component1` will not be treated as a Zephyr
 library. To create a Zephyr library in Zephyr CMake kernel mode consider
 creating a Zephyr module.  See more here:
 https://docs.zephyrproject.org/latest/guides/modules.html
Call Stack (most recent call first):
 /home/user/work/GIT/zephyrproject/zephyr/cmake/modules/extensions.cmake:464 (zephyr_append_cmake_library)
 CMakeLists.txt:50 (zephyr_library_named)

Could you advise on how to avoid these warnings? Will they disappear once we move all zephyr_library_named entries into a separate Zephyr module that we then consume in our sample app? Any further recommendations for us?

Thank you for your assistance!

[TK5090]

I assume your library is located in a Git repository? Let west check out this library; then west will find your library during compilation.
To allow west to check out the library, your library must be listed as a project in your manifest west.yml or in a submanifest like zephyr.yml.

https://docs.zephyrproject.org/latest/develop/modules.html

[thedjnK]

Technically, using zephyr_library_named to create static libraries that users can link to their applications seems feasible

No, this is not supported, the point in static libraries is you build a static library that has no relation to zephyr then use it from within zephyr, not build zephyr with static libraries then use said static libraries in other zephyr (or non-zephyr) projects, the latter is a complete minefield full of pitfalls that if you think is a good idea, you do not understand how zephyr or the build system works (because it is not, you can experiment with this by setting a Kconfig, building a "static library" then including said static library with an application with a different value for the same Kconfig, the library is inherently broken/faulty/deficient by design)

[thorsten-klein]

Yes, I fully agree that using static libraries as blobs is a minefield full of pitfalls. But this is not how we want to use them.
We want to build those static libraries just as "intermediate artifacts" within our build. So of course we use this "mono build" which is fully configured by setting a Kconfig.