Does CPM work with CMakePresets?

[janos-ijgyarto]

Hi all,

I have a somewhat complicated project setup, where I use CMakePresets combined with VS 2022 to manage different configurations (compiler, generator, platform, etc.) Because of how CMakePresets currently works, practically every one of the variables will require a whole different config preset, and thus a whole new configuration. For builds, this was not a problem, I could just set it so CMake's output and the binaries would be placed in a subfolder named after the config preset.

The problems began when I tried to combine this with FetchContent. Because of how it works, it wasn't possible to "share" the fetched libraries between different build configs. Ideally all I want is that I fetch the sources once, configure if needed (some libraries are header-only and don't even contain a CMakeLists.txt), and output the builds based on the current configuration (i.e make it behave as a package manager)

With how FetchContent works, however, I had to set the FetchContent base directory within the config-specific subfolder, which means I had to re-fetch every dependency for every different configuration (including when I just swap between debug and release). There is a thread on the CMake forums which illustrates the issue.

Does CPM offer a way around this? Or would I end up having the same issue?

[TheLartians]

Not sure I understand the problem 100%, but would setting the CPM_SOURCE_CACHE environment variable solve the issue? That way any dependencies added with CPM will be downloaded to the source cache directory only once for all projects that share the same cache.

[audricschiltknecht]

Hello,

I've got the same initial question.
For me, that would allow to define a set of CMake variables in a preset of a library and abstract them for our users, who can then simply use the "user" preset, instead of having to manually specify each CMake variable as an option when adding a dependency via CPM.

[oceanofthelost]

@janos-ijgyarto, one way around having to have a separate configuration per compiler, generator, etc, is to use a multi config generator. Currently CMake supports two, Ninja Multi-Config and Visual Studio.

When using a CMakePreset, build and test presents need to explicitly set configuration in order have the correct configuration built.

With this setup, a single build step or workflow can be used and CPM will work as expected.

If a multi-config generator cannot be used, then CPM cache will need to be set and shared across projects.