GEOS snippet in Wiki is unclear

[lindsaySFS]

The snippit is currently:

set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${GEOS_SOURCE_DIR}/cmake")

CPMAddPackage(
  NAME geos
  GITHUB_REPOSITORY libgeos/geos
  GIT_TAG 3.8.1
)

But it's unclear how GEOS_SOURCE_DIR would be set. My understanding is that a variable called geos_SOURCE_DIR would be defined after CPMAddPackage is called. Is there a way to get the source directory beforehand?

I don't actually need GEOS, but another library with the same problem, where I need to add to the CMAKE_MODULE_PATH before calling CPMAddPackage.

[lindsaySFS]

I made it work for my case by:

1. use CPMAddPackage with DOWNLOAD_ONLY True
2. Append to CMAKE_MODULE_PATH with now populated _SOURCE_DIR
3. Add the project with add_subdirectory

But this feels pretty hacky. I guess ideally the project would set the CMAKE_MODULE_PATH correctly, but it would also be nice if there is a better way to manually set it, that plays nicely with CPM.