CPM_<dep>_SOURCE does not load project

[Tetragramm]

This might be two bugs, or the problems could be related.

I have a project (call it MainLib) that is included in FinalProj by CPMAddPackage. MainLib uses CPMAddPackage to include multiple dependencies LibA, LibB, ect.

When I build FinalProj with CPM_MainLib_SOURCE set to a local copy of the source, the dependencies are not included.

First problem: FetchContent_Populate

CMake Warning (dev) at /usr/share/cmake-3.30/Modules/FetchContent.cmake:1953 (message):
[cmake]   Calling FetchContent_Populate(MainLib) is deprecated, call
[cmake]   FetchContent_MakeAvailable(MainLib) instead.  Policy CMP0169 can be set
[cmake]   to OLD to allow FetchContent_Populate(MainLib) to be called directly for
[cmake]   now, but the ability to call it with declared details will be removed
[cmake]   completely in a future version.
[cmake] Call Stack (most recent call first):
[cmake]   /home/me/Source/CPM_cache/cpm/CPM_0.40.8.cmake:1139 (FetchContent_Populate)
[cmake]   /home/me/Source/CPM_cache/cpm/CPM_0.40.8.cmake:917 (cpm_fetch_package)
[cmake]   /home/me/Source/CPM_cache/cpm/CPM_0.40.8.cmake:711 (CPMAddPackage)
[cmake]   /home/me/Source/FinalProj/CMakeLists.txt:19 (cpmaddpackage)
[cmake] This warning is for project developers.  Use -Wno-dev to suppress it.

Using cmake_policy(SET CMP0169 OLD) does not remove this error. set(CMAKE_POLICY_DEFAULT_CMP0169 OLD) does.

Once that is suppressed, it reports success.
[cmake] -- CPM: Adding package MainLib@ (~/Source/MainLib/)
But it does not log the inclusion of the dependencies the way it does when CPM_MainLib_SOURCE is not set.

That would look like

[cmake] -- CPM: MainLib: Adding package LibA@1.15.0 (v1.15.0 at /home/me/Source/CPM_cache/LibA/7251ead404dccd824789f8f3a13df2a6fb56440c/LibA)
[cmake] -- CPM: MainLib: Adding package LibB@1.0.3 (1.0.3 at /home/me/Source/CPM_cache/LibB/e91eb1dcff97b3aba7576745a2dcd030fdec5378/LibB)

Cmake version is 3.30.2
CPM version is 0.40.8

[itavero]

For what it's worth, I also see these warnings a lot with CMake 4.0.
Seems like CPM.cmake might need an update to remain compatible, @TheLartians ?

[iboB]

There's actually a bug in CMake (fixed in 3.30.3) which was handled in CPM through #605

So it seems to me that there's a narrow window of CMake versions 3.30.0 (introducing cmp0169) and 3.30.2 (prior to fixing https://gitlab.kitware.com/cmake/cmake/-/issues/26243) which will lead to the behavior in this issue.

@Tetragramm can you try this using CMake 3.30.3 or later?