CppInfo Components internal requirements

[danimtb]

Changelog: Feature: Implements cpp_info.components dependencies.
Docs: conan-io/docs#1682

#tags: slow

• Refer to the issue that supports this Pull Request: closes [feature] Components: implement internal dependencies and link order resolution #6716
• If the issue has missing info, explain the purpose/use case/pain/need that covers this Pull Request.
• I've read the Contributing guide.
• I've followed the PEP8 style guides for Python code.
• I've opened another PR in the Conan docs repo to the develop branch, documenting this one.

^{Note: By default this PR will skip the slower tests and will use a limited set of python versions. Check here how to increase the testing level by writing some tags in the current PR body text.}

[jgsogo]

Some comments over the tests, I've been having a look mostly to the functionality, not the implementation

[memsharded]

Probably way simpler and faster to sort in the opposite order: check that the current components requires are None or all in ordered.

[danimtb]

I implemented that logic before and it was a mess calculating the link order later. I'd like to keep it as is for now and improve the speed in the future if needed

[memsharded]

When lazy/caching, this is better checked against None if self._sorted_components is None, to avoid firing again computations when result is an empty dict, list or set.

[memsharded]

Also as a oneliner: if any(comp_name == name for comp_name in self.components)

[jgsogo]

I'm missing a test here, but I don't know how to make it. Maybe you have an idea:

I need a package llvm using components that require another package openssl. I want to see that components from llvm need to require openssl explicitly in order to work (because it has to be explicit, right?):

OpenSSL recipe: any recipe not using components

LLVM recipe

class LLVM(ConanFile):
    name = 'llvm'
    requires = "openssl/1.1.1z"

    def package_info(self):
        self.cpp_info.components["tooling"].requires["openssl::openssl"]

        # What happens with this line in this PR? By now it should work the same as the previous one? raise? ignore?
        self.cpp_info.components["unwind"].requires["openssl::crypto"]

People will start to use components and we want them to add the .requires["openssl::openssl"] so it will work in the next Conan iteration with the "enhanced-generators". Otherwise people will need to change their recipes again with the next version.

I really don't know if it is worth to check it in the sources (at least for CMake I imagine a weird if clause in the CMake file) or just write it big and clear in the docs.

[memsharded]

People will start to use components and we want them to add the .requires["openssl::openssl"] so it will work in the next Conan iteration with the "enhanced-generators". Otherwise people will need to change their recipes again with the next version.

You mean to force the definition of at least one components["some_comp"].requires to each one of the current direct package requires definition, and otherwise it will be an error, right? Yes, this would be a nice addition if not too complex, to avoid badly-defined recipes.

It should be clearly documented that when defining components, it is not assumed a dependency to the required packages, and it should be explicit.

[jgsogo]

Easier than expected. Thanks for this extra effort \o/

[memsharded]

It seems that you were hit by your own check in another test: package_info_components_test()

[danimtb]

Added docs!

[jgsogo]

🎁 Ready to go!