[Discussion] Install-based caching for libraries not suited for add_subdirectory

[TobiasWallner]

First off i really enjoy your project and it has helped me tremendously in the past.

However, sometimes i come across a library that is not written to be used with add_subdirectory, it is written to be installed and used with find_package.

If not used with find_package all sorts off issues can arise from:

• are not designed to be consumed via add_subdirectory
• assume they are the top-level project
• expose un-namespaced targets that clash with other dependencies
• rely on install-time configuration logic
• enable tests/examples by default when included as a subproject

So based on CPM.cmakes source caching and CMake only idea i experimented with a small complementary tool: https://github.com/TobiasWallner/BPM.cmake

It provides: BPMInstallPackage with:

• Git source caching (similar to CPM)
• A manifest-based hash derived from: compiler ID + version, toolchain file (if present), build flags, user-provided CMake arguments, etc. (all things CMake knows)
• Install directories per hash
• find_package(... CONFIG NO_DEFAULT_PATH) against that install

This effectively creates an light weight install cache per build configuration, while keeping CPM available for normal source-based dependencies.

I’m currently using it alongside CPM as an opt-in for libraries that don’t behave well as subprojects.

I would be interested in your thoughts:

• Do you see value in this pattern (fingerprinted installs and maybe even build caches) for CPM.cmake?
• Would it make sense to document this as an advanced/opt-in integration strategy?
• Or do you feel this is outside the intended scope of CPM?

Thanks again for the great tool.

Looking forward.