CMake 2.24 Dependency Provider

[chfast]

CMake 2.24 is going to introduce a new feature called Dependency Providers. In essence, user will be able to setup a single dependency provider for a project. And the job of the dependency provider is to deliver dependency by intercepting find_package() and FetchContent_MakeAvailable() commands.

It would be very nice to adapt CPM to the Dependency Provider role.

[itavero]

An example provider can also be found in the CMake documentation.

I think this is an interesting concept, but at the same time, I don't think you can make this really "portable".
find_package will have to be passed a package name that makes sense to CPM.cmake.
For that you either need specific names, or additional "middleware" that transforms it.
And, if you need middleware to transform it, making the integration with CPM.cmake yourself does not seem to be a whole lot more work.

But then again, I'm also not 100% sure how the developers of CMake envisioned this to be used, so maybe my expectations are a bit off as well.

[chfast]

I make a PoC using FetchContent for declaring dependencies. It feels a bit weird to use FetchContent to call CPM which uses FetchContent under the hood, but it works.

CMakeLists.txt

cmake_minimum_required(VERSION 3.24)
project(cpm_dep_prov)

include(FetchContent)
FetchContent_Declare(
    argparse
    GIT_REPOSITORY https://github.com/p-ranav/argparse.git
    GIT_TAG v2.9
)
FetchContent_MakeAvailable(argparse)

set(BENCHMARK_ENABLE_TESTING FALSE)
FetchContent_Declare(
    benchmark
    GIT_REPOSITORY https://github.com/google/benchmark
    GIT_TAG v1.7.1
)
FetchContent_MakeAvailable(benchmark)

add_executable(cpm_dep_prov main.cpp)
target_link_libraries(cpm_dep_prov PRIVATE argparse::argparse benchmark::benchmark)

cpm_provider.cmake

include(CPM.cmake)
include(FetchContent)

function(cpm_provide_dependency METHOD NAME)
    CPMAddPackage(NAME ${NAME} GIT_REPOSITORY ${ARGV7} GIT_TAG ${ARGV9})
    FetchContent_SetPopulated(${NAME} SOURCE_DIR ${${NAME}_SOURCE_DIR} BINARY_DIR ${${NAME}_BINARY_DIR})
endfunction()

cmake_language(
    SET_DEPENDENCY_PROVIDER cpm_provide_dependency
    SUPPORTED_METHODS FETCHCONTENT_MAKEAVAILABLE_SERIAL
)

CMake log

-- The C compiler identification is GNU 12.2.0
-- The CXX compiler identification is GNU 12.2.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- CPM: Adding package argparse@2.9 (v2.9)
-- CPM: Adding package benchmark@1.7.1 (v1.7.1)
-- Failed to find LLVM FileCheck
-- Found Git: /usr/bin/git (found version "2.37.2") 
-- git version: v1.7.1 normalized to 1.7.1
-- Version: 1.7.1
-- Looking for shm_open in rt
-- Looking for shm_open in rt - found
-- Performing Test HAVE_CXX_FLAG_WALL
-- Performing Test HAVE_CXX_FLAG_WALL - Success
-- Performing Test HAVE_CXX_FLAG_WEXTRA
-- Performing Test HAVE_CXX_FLAG_WEXTRA - Success
-- Performing Test HAVE_CXX_FLAG_WSHADOW
-- Performing Test HAVE_CXX_FLAG_WSHADOW - Success
-- Performing Test HAVE_CXX_FLAG_WFLOAT_EQUAL
-- Performing Test HAVE_CXX_FLAG_WFLOAT_EQUAL - Success
-- Performing Test HAVE_CXX_FLAG_WERROR
-- Performing Test HAVE_CXX_FLAG_WERROR - Success
-- Performing Test HAVE_CXX_FLAG_WSUGGEST_OVERRIDE
-- Performing Test HAVE_CXX_FLAG_WSUGGEST_OVERRIDE - Success
-- Performing Test HAVE_CXX_FLAG_PEDANTIC
-- Performing Test HAVE_CXX_FLAG_PEDANTIC - Success
-- Performing Test HAVE_CXX_FLAG_PEDANTIC_ERRORS
-- Performing Test HAVE_CXX_FLAG_PEDANTIC_ERRORS - Success
-- Performing Test HAVE_CXX_FLAG_WSHORTEN_64_TO_32
-- Performing Test HAVE_CXX_FLAG_WSHORTEN_64_TO_32 - Failed
-- Performing Test HAVE_CXX_FLAG_FSTRICT_ALIASING
-- Performing Test HAVE_CXX_FLAG_FSTRICT_ALIASING - Success
-- Performing Test HAVE_CXX_FLAG_WNO_DEPRECATED_DECLARATIONS
-- Performing Test HAVE_CXX_FLAG_WNO_DEPRECATED_DECLARATIONS - Success
-- Performing Test HAVE_CXX_FLAG_WNO_DEPRECATED
-- Performing Test HAVE_CXX_FLAG_WNO_DEPRECATED - Success
-- Performing Test HAVE_CXX_FLAG_WSTRICT_ALIASING
-- Performing Test HAVE_CXX_FLAG_WSTRICT_ALIASING - Success
-- Performing Test HAVE_CXX_FLAG_WD654
-- Performing Test HAVE_CXX_FLAG_WD654 - Failed
-- Performing Test HAVE_CXX_FLAG_WTHREAD_SAFETY
-- Performing Test HAVE_CXX_FLAG_WTHREAD_SAFETY - Failed
-- Performing Test HAVE_CXX_FLAG_COVERAGE
-- Performing Test HAVE_CXX_FLAG_COVERAGE - Success
-- Compiling and running to test HAVE_STD_REGEX
-- Performing Test HAVE_STD_REGEX -- success
-- Compiling and running to test HAVE_GNU_POSIX_REGEX
-- Performing Test HAVE_GNU_POSIX_REGEX -- failed to compile
-- Compiling and running to test HAVE_POSIX_REGEX
-- Performing Test HAVE_POSIX_REGEX -- success
-- Compiling and running to test HAVE_STEADY_CLOCK
-- Performing Test HAVE_STEADY_CLOCK -- success
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE  
-- Configuring done
-- Generating done

[TheLartians]

Thanks for the POC, it does indeed feel weird to use FetchContent to call CPM which uses FetchContent.
I think one use-case could be to use this for easily getting CPM features like caching and lock file in projects currently built for FetchContent.

As CPM forwards all origin parameters to FetchContent, maybe it could even be made more generic by forwarding all extra arguments here as well?

function(cpm_provide_dependency METHOD NAME)
    CPMAddPackage(NAME ${NAME} ${ARGN})
    FetchContent_SetPopulated(${NAME} SOURCE_DIR ${${NAME}_SOURCE_DIR} BINARY_DIR ${${NAME}_BINARY_DIR})
endfunction()