[RFC] Two recipes for regular flex and flex_installer in one repo: use python_requires

[madebr]

In response to bincrafters/community#625

This pr is very similar to #4 in that it creates multiple recipes in one repo.
This main difference is that this one is using python_requires.
This allows the common logic to be put in a common base class flex_base, which is subclassed by flex_installer and flex.

Imho, it looks much cleaner.
But alas, it has a major problem (and showstopper):

• The python_requires in the flex and flex_installer recipe requires a full conan reference.
  In this pr, this reference is hardcoded to flex_base/2.6.4@bincrafters/stable which is not correct.
  The username and channel of flex_base should default to be the same as the username and channel of the flex_installer and flex recipe.

I do not know whether this is a limitation of python_requires or a limitation of my knowledge.
Imho, a ConanFile class should have the ability to override the username and channel of a python_requires.
Please comment if you know how to fix this.

Notes:

• depends on Common builds correct dir conan-io/conan-package-tools#325
• depends on python_requires fails when remote is in CONAN_REMOTES but not added to conan conan-io/conan-package-tools#331
• I don't like the logic to export and upload flex_base in build.py

[jgsogo]

@madebr, about the python_requires issue I can point you to this comment conan-io/conan#4355 (comment), Conan needs to know which python_requires to use (flex_base) before trying to resolve the recipe (flex). The reason for this is that a python-requires might affect how the reference is computed and thus the pyreq should be fully resolved before, think about something like this:

base = python_requires("name/version@user/channel")

class MyLib(ConanFile):
    name = "mylib"
    version = base.compute_my_version()

how could I know MyLib::version without locking the base = python_req...?

[madebr]

@jgsogo Thanks for the tip. Good to know that an explicit version is required in derived conan classes.

My main problem/question remains though: the dependency on flex_base/2.6.4@bincrafters/stable is explicit. This will make it impossible to create a flex package for the testing channel without changing the string to flex_base/2.6.4@bincrafters/testing.

In other words, this is impossible:

conan export flex_base someuser/somechannel
conan create flex_installer someuser/somechannel
conan create flex someuser/somechannel

[jgsogo]

It cannot depend on the version of the recipe that is using the python requires, but you can do this without any problem:

username = os.getenv("CONAN_USERNAME")
channel = os.getenv("CONAN_CHANNEL")

base = python_requires("flex_base/2.6.4@{}/{}".format(username, channel))

class MyLib(base.ConanFile):
    name = "flex"
    ...

and those env variables can be populated from the command line or CI itself.

[madebr]

@jgsogo
The problem with that approach is that those variables are not defined when this package is used as a dependency.

If a package has a build_requires("flex_installer/2.6.4@bincrafters/stable"), an error will be thrown because flex_base/2.6.4@None/None is not found.
Using a default in get_env is also not appropriate.

Apart from that, I don't think it is good design to let environment variables define dependencies.
The dependency graph should be independent of environment variables.

[jgsogo]

Now I understand your problem, this is more related to this other issue (conan-io/conan#3988). I think we haven't come up with a solution yet 😞

[SSE4]

outdated by #7