Use a CMake macro packaged in a dependency

When a package recipe wants to provide a CMake functionality via a macro, it can be done as follows. Let’s say that we have a pkg recipe, that will “export” and “package” a Macros.cmake file that contains a pkg_macro() CMake macro:

pkg/conanfile.py

from conan import ConanFile
from conan.tools.files import copy

class Pkg(ConanFile):
    name = "pkg"
    version = "0.1"
    package_type = "static-library"
    # Exporting, as part of the sources
    exports_sources = "*.cmake"

    def package(self):
        # Make sure the Macros.cmake is packaged
        copy(self, "*.cmake", src=self.source_folder, dst=self.package_folder)

    def package_info(self):
        # We need to define that there are "build-directories", in this case
        # the current package root folder, containing build files and scripts
        self.cpp_info.builddirs = ["."]

pkg/Macros.cmake

function(pkg_macro)
    message(STATUS "PKG MACRO WORKING!!!")
endfunction()

When this package is created (cd pkg && conan create .), it can be consumed by other package recipes, for example this application:

app/conanfile.py

from conan import ConanFile
from conan.tools.cmake import CMake

class App(ConanFile):
    package_type = "application"
    generators = "CMakeToolchain"
    settings = "os", "compiler", "arch", "build_type"
    requires = "pkg/0.1"

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

That has this CMakeLists.txt:

app/CMakeLists.txt

cmake_minimum_required(VERSION 3.15)
project(App LANGUAGES NONE)

include(Macros)  # include the file with the macro (note no .cmake extension)
pkg_macro()  # call the macro

So when we run a local build, we will see how the file is included and the macro called:

$ cd app
$ conan build .
PKG MACRO WORKING!!!