Hi @TheLartians and @threeal

I too have some issues with my package, in regards to appending a module path to CMAKE_MODULE_PATH.
Basically, whenever I install the package using cmake's native FetchContent_Declare, it appears to work (which might just be luck - only works if I use FetchContent from my consuming project's root level CMakeLists.txt file.). This is most likely because FetchContent_MakeAvailable() appears to include my package's CMakeLists.txt via add_subdirectory().

include(FetchContent)
FetchContent_Declare(
 "rsp-cmake-scripts"
 GIT_REPOSITORY "https://github.com/rsps/cmake-scripts"
 GIT_TAG "43febe92df4a06a31338e380eb2dc64683f8a273" # Commit hash for now, version not yet released.
)
FetchContent_MakeAvailable("rsp-cmake-scripts")
include("rsp/debug") # Works
dump(CMAKE_MODULE_PATH) # Works

But, when trying to fetch my package using CPM, any changes to CMAKE_MODULE_PATH are not propagated out of the CPMAddPackage() function. E.g.:

CPMAddPackage(
 NAME "rsp-cmake-scripts"
 GIT_TAG "43febe92df4a06a31338e380eb2dc64683f8a273" # Commit hash for now, version not yet released.
 # VERSION "${RSP_CMAKE_SCRIPTS_VERSION}"
 GITHUB_REPOSITORY "rsps/cmake-scripts"
 OPTIONS "RSP_ENABLE_ANSI true"
)
include("rsp/debug") # CMake Error: include could not find requested file: rsp/debug
dump(CMAKE_MODULE_PATH) # ...not reached

Experiment A (failed)

I have locally attempted to set the CMAKE_MODULE_PATH in the parent scope, by modifying the cpm_export_variables() macro:

macro(cpm_export_variables name)
 # ... previous not shown ...
 # Attempt to propagate eventual appended CMAKE_MODULE_PATH paths to parent
 set(CMAKE_MODULE_PATH "${CMAKE_MODULE_PATH}" PARENT_SCOPE)
endmacro()

Sadly, the above change had no effect. My package's module path isn't available.

Experiment B

Same as "Experiment A", but with an additional modification to cpm_fetch_package():

function(cpm_fetch_package PACKAGE DOWNLOAD_ONLY populated)
 # ... previous not shown ...
 set(${PACKAGE}_SOURCE_DIR
 ${${lower_case_name}_SOURCE_DIR}
 PARENT_SCOPE
 )
 set(${PACKAGE}_BINARY_DIR
 ${${lower_case_name}_BINARY_DIR}
 PARENT_SCOPE
 )
 # Attempt to propagate eventual appended CMAKE_MODULE_PATH paths to parent - allows
 # cpm_export_variables() to propagate change upwards...
 set(CMAKE_MODULE_PATH "${CMAKE_MODULE_PATH}" PARENT_SCOPE)
endfunction()

This seems to work in my case, yet I'm not sure if other CPM functions need to be modified?

For now, I do not see any viable work-around on how to make this work as desired. It is not uncommon for packages, libraries, ...etc, to append paths to CMAKE_MODULE_PATH, such that consuming projects are able to make use of cmake utilities, custom paths, or resources that are somehow made available.

In any case, I really hope that CPM can make this work.

In addition to the previous comment, the problem is actually not just for appended paths to CMAKE_MODULE_PATH, but basically every kind of variable that a "package" attempts to expose in a parent scope!

I'm not sure what a correct solution would be (I'm not a CMake expert... I'm still struggling to understand the basics).