Add find_package overrides that also work in CONFIG mode (#498)

[patstew]

CPM currently adds a FindFoo.cmake to the module path to override subsequent find_package calls. This makes sure that works when the find_package call is in CONFIG mode as well. Some of my dependencies use this in their CMakeLists.txt. This is equivalent to the OVERRIDE_FIND_PACKAGE argument to FetchContent, we could add that option to CPMAddPackage, but it seems like this is the intended default behaviour of CPM?

The include(....-extra.cmake) bits are something FetchContent does that's also useful here. They should maybe be added to the Find*.cmake version too?

Fixes #498

[TheLartians]

Thanks a lot for the PR and sorry for taking long to review it! It looks great on first glance, I have one small suggestion for readability. Also I'm not sure why the CI pipelines are not running, do you need to enable GitHub actions for your fork?

[patstew]

No worries, thanks for CPM.
I have added some documentation.
I think you need to approve it to run the tests https://docs.github.com/en/actions/managing-workflow-runs-and-deployments/managing-workflow-runs/approving-workflow-runs-from-public-forks
There should be an "Approve and Run" button somewhere for you?

[TheLartians]

There should be an "Approve and Run" button somewhere for you?

Yep this time it showed the button, thanks for update!

Looks like we need to update the tests to support the different behavior based on the CMake version and also run
The code formatter (see here for more info).

[patstew]

I think I've fixed the issues (patstew#1). I've also added a few checks to the modules.cmake test so that it fails without the fixes in this commit, and ensures the fallback to the old method works. I've got rid of the simple check that FindA.cmake exists and reinstated the check that find_package works instead. Was there was a reason for the find_package to be disabled previously?

[TheLartians]

Looks great, thanks for updating this feature and the according documentation and test changes!

Was there was a reason for the find_package to be disabled previously?

Probably an oversight, good catch!

[TheLartians]

Changes released in v0.40.3 🎉

[jay3d]

This change breaks my configuration that worked in v0.40.2 before.
I have two packages that are added via CPM, and one is dependent on the other, now the "next" package won't find the first one anymore after this change, that was working fine before by default:

CPMAddPackage(
        NAME TBB
        GIT_REPOSITORY https://github.com/oneapi-src/oneTBB.git
        GIT_TAG v2021.13.0
        EXCLUDE_FROM_ALL YES
        SYSTEM YES
)

CPMAddPackage(
        NAME OpenSubdiv
        GIT_REPOSITORY https://github.com/PixarAnimationStudios/OpenSubdiv.git
        GIT_TAG v3_6_0
        EXCLUDE_FROM_ALL YES
        SYSTEM YES
)

Now it can't find TBB anymore in .3 and above.