Use cmake modules inside a tool_requires transparently

When we want to reuse some .cmake scripts that are inside another Conan package there are several possible different scenarios, like if the .cmake scripts are inside a regular requires or a tool_requires.

Also, it is possible to want 2 different approaches:

  • The consumer of the scripts can do a explicit include(MyScript) in their CMakeLists.txt. This approach is nicely explicit and simpler to setup, just define self.cpp_info.builddirs in the recipe, and consumers with CMakeToolchain will automatically be able to do the include() and use the functionality. See the example here
  • The consumer wants to have the dependency cmake modules automatically loaded when the find_package() is executed. This current example implements this case.

Let’s say that we have a package, intended to be used as a tool_require, with the following recipe:

import os
from conan import ConanFile
from import copy

class Conan(ConanFile):
    name = "myfunctions"
    version = "1.0"
    exports_sources = ["*.cmake"]

    def package(self):
        copy(self, "*.cmake", self.source_folder, self.package_folder)

    def package_info(self):
        self.cpp_info.set_property("cmake_build_modules", ["myfunction.cmake"])

And a myfunction.cmake file in:

    message("Hello myfunction!!!!")

We can do a cd myfunctions && conan create . which will create the myfunctions/1.0 package containing the cmake script.

Then, a consumer package will look like:

from conan import ConanFile
from import CMake, CMakeDeps, CMakeToolchain

class Conan(ConanFile):
    settings = "os", "compiler", "build_type", "arch"
    tool_requires = "myfunctions/1.0"

    def generate(self):
        tc = CMakeToolchain(self)

        deps = CMakeDeps(self)
        # By default 'myfunctions-config.cmake' is not created for tool_requires
        # we need to explicitly activate it
        deps.build_context_activated = ["myfunctions"]
        # and we need to tell to automatically load 'myfunctions' modules
        deps.build_context_build_modules = ["myfunctions"]

    def build(self):
        cmake = CMake(self)

And a CMakeLists.txt like:

cmake_minimum_required(VERSION 3.0)
find_package(myfunctions CONFIG REQUIRED)

Then, the consumer will be able to automatically call the myfunction() from the dependency module:

$ conan build .
Hello myfunction!!!!

If for some reason the consumer wants to force the usage from the tool_requires() as a CMake module, the consumer could do deps.set_property("myfunctions", "cmake_find_mode", "module", build_context=True), and then find_package(myfunctions MODULE REQUIRED) will work.