Issue not finding BuildType.cmake when building via CMake's FetchContent

[apthorpe]

I'm building a standalone application that depends on FLPR and I am using CMake for my build system. Recent-ish versions of CMake allow for downloading and building remote dependencies with the ExternalProject and FetchContent facilities. FetchContent is especially nice for including dependencies that also use CMake. So, for example, my application's CMakeFiles.txt contains:

include(FetchContent)
set(FLPR_SOURCE_DIR "${CMAKE_CURRENT_BINARY_DIR}/FLPR-source")
FetchContent_Declare(FLPR
  GIT_REPOSITORY https://github.com/lanl/FLPR.git
  GIT_TAG        HEAD
  SOURCE_DIR     "${FLPR_SOURCE_DIR}"
)
FetchContent_MakeAvailable(FLPR)

which will retrieve the FLPR source from GitHub and place it in build/FLPR-source, then perform some CMake magic to build it. So far, so good: you should see this pull and attempt to build FLPR with CMake.

The issue seems to be one of CMake module detection and pathing; the build fails with:

CMake Error at build/FLPR-source/CMakeLists.txt:18 (include):
  include could not find load file:

    BuildType


CMake Error at build/FLPR-source/CMakeLists.txt:19 (include):
  include could not find load file:

    CompilerFlags

Both BuildType.cmake and CompilerFlags.cmake exist under build/FLPR-source/cmake with appropriate permissions (as expected) but it seems like CMake is searching for them under <my project root>/cmake instead (where it should look for these files when it's normally built as a standalone project). That is, the errors disappear if I copy BuildType.cmake and CompilerFlags.cmake to <my project root>/cmake.

I believe the critical lines of FLPR's CMakeLists.txt are

# Allow CMake to find some project include files
list (INSERT CMAKE_MODULE_PATH 0 "${CMAKE_SOURCE_DIR}/cmake")

but I don't have a good idea of how to appropriately set CMAKE_MODULE_PATH in a submodule; what's needed is the child's version of "${CMAKE_SOURCE_DIR}/cmake", not the parent's.

I'm not sure if this configuration mismatch is on my side or not; I'm still digging into it.

[apthorpe]

This may be a simple fix; reviewing some of my other CMakeFiles.txt configs, I find I'm including CMake scripts with:

include("${CMAKE_CURRENT_SOURCE_DIR}/cmake/FetchFLPR.cmake")

Maybe change CMAKE_SOURCE_DIR to CMAKE_CURRENT_SOURCE_DIR in FLPR's CMakeLists.txt? I checked it locally and it doesn't seem to affect the standalone build.

Also, as an alternative/workaround, I have had success with including FLPR as an ExternalProject (see attachment)
BuildFLPR.zip

[pjh40]

That is cool CMake feature! Seems nicer than doing a 'git submodule', which is what I'm doing to build an app that depends on FLPR.

[apthorpe]

I have had better luck with ExternalProject but I thought I'd give FetchContent another try. One nice thing about ExternalProject is that it can deal with projects that don't use CMake or have weird build processes beyond the standard configure && make && make install. Especially on Windows. It's not exactly pleasant, but it is both possible and portable.