[question] Why is the default component name not checked when resolving components with check_components_exist?

[Kogzedri]

What is your question?

I've created a library created with several components in the following manner:

class ExampleRecipe(ConanFile):
    name = "example"
    version= "1.0.0"
    package_type = "header-library"

    settings = "os", "compiler", "build_type", "arch"

    exports_sources = "CMakeLists.txt", "src/*"          

    def layout(self):
        cmake_layout(self)
    
    def generate(self):
        deps = CMakeDeps(self)
        deps.generate()
        tc = CMakeToolchain(self)
        tc.generate()

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

    def package(self):
        cmake = CMake(self)
        cmake.install()
    
    def package_info(self):
        self.cpp_info.components["asdf"].requires = []

When trying to consume the above library:

class ConsumerRecipe(ConanFile):
    ...
   def requirements(self):
        self.requires('example/1.0.0')
    def generate(self)
        deps = CMakeDeps(self)
        deps.check_components_exist=True
        deps.generate()
        tc = CMakeToolchain(self)
        tc.generate()
    ...

find_package(example REQUIRED COMPONENTS asdf)
set(${tgt} consume_test)
add_executable(${tgt})
...
target_link_libraries(${tgt}
    PRIVATE
        example::asdf
)

Relevant output:

======== Calling build() ========
conanfile.py (consume_test/1.0.0): Calling build()
conanfile.py (consume_test/1.0.0): Running CMake.configure()
conanfile.py (consume_test/1.0.0): RUN: cmake -G "Unix Makefiles" -DCMAKE_TOOLCHAIN_FILE="generators/conan_toolchain.cmake" -DCMAKE_INSTALL_PREFIX="/path/to/consume_test" -DCMAKE_POLICY_DEFAULT_CMP0091="NEW" -DCMAKE_BUILD_TYPE="Release" "/path/to/consume_test"
-- Using Conan toolchain: /path/to/consume_test/build/Release/generators/conan_toolchain.cmake
-- Conan toolchain: Defining architecture flag: -m64
-- Conan toolchain: C++ Standard 17 with extensions ON
-- Conan: Component target declared 'example::asdf'
-- Conan: Target declared 'example::example'
CMake Error at build/Release/generators/example-config.cmake:48 (message):
  Conan: Component 'asdf' NOT found in package 'example'
Call Stack (most recent call first):
  src/CMakeLists.txt:1 (find_package)

When specifying CMakeDeps.check_components_exists, only the strict component name seems to get checked. The generated CMake code doesn't check the default namespaced package_name::component target, despite it being declared earlier during processing.

The culprit seems to be here: config.py, checking only if(TARGET _FIND_COMPONENT)

My ultimate question boils down to: why is the above template CMake code not checking: if((TARGET _FIND_COMPONENT) OR (TARGET ${CMAKE_FIND_PACKAGE_NAME}::${_FIND_COMPONENTS})? Does that cause some kind of other problem that I'm just not seeing?

Have you read the CONTRIBUTING guide?

• I've read the CONTRIBUTING guide

[memsharded]

Hi @Kogzedri

Thanks for your question.

This is a known limitation of the current CMakeDeps generator.
See the following unit test:

def test_components_required():
    # https://github.com/conan-io/conan/issues/17689
    conanfile = textwrap.dedent("""
        from conan import ConanFile
        class ExampleRecipe(ConanFile):
            name = "example"
            version = "1.0.0"
            package_type = "header-library"
            settings = "os", "compiler", "build_type", "arch"
            exports_sources = "CMakeLists.txt", "src/*"

            def package_info(self):
                self.cpp_info.components["asdf"].requires = []
        """)
    consumer = textwrap.dedent("""
        from conan import ConanFile
        from conan.tools.cmake import CMakeDeps, CMakeToolchain, CMake
        class ConsumerRecipe(ConanFile):
            settings = "os", "arch", "compiler", "build_type"
            def requirements(self):
                self.requires('example/1.0.0')
            def generate(self):
                deps = CMakeDeps(self)
                deps.check_components_exist=True
                deps.generate()
                CMakeToolchain(self).generate()
            def build(self):
                cmake = CMake(self)
                cmake.configure()
                cmake.build()
        """)
    cmake = textwrap.dedent("""
        cmake_minimum_required(VERSION 3.15)
        project(consumer)
        find_package(example REQUIRED COMPONENTS example::asdf)
        """)
    c = TestClient()
    c.save({"example/conanfile.py": conanfile,
            "consumer/conanfile.py": consumer,
            "consumer/CMakeLists.txt": cmake})
    c.run("create example")
    c.run("build consumer")
    print(c.out)
    # seems to work fine

Note it has to use the COMPONENTS as the example::asdf, not the asdf alone. That might be changed using the set_property("cmake_target_name"), but by default, it requires the full name.

This has already been improved in the new "incubating" CMakeDeps generator, see https://docs.conan.io/2/incubating.html

It can be validated in the above test, changing

    find_package(example REQUIRED COMPONENTS asdf)
    ...
    c.run("build consumer -c tools.cmake.cmakedeps:new=will_break_next")

Also, the deps.check_components_exist=True is not necessary in the incubating new CMakeDeps, component validation is done by default.