Problem description

In pypi packaging you have the concept of environment markers, which can help you to optionally install a dependency. We've had requests of people wanting to use this to exclude certain dependencies according to the python version e.g:

pkg = { path ="./my-pkg", env-markers = ["python_version < '3.11'"] }

Because we re-create the PEP508 requirements, it would be easy to add and this is already taken into account in the satisfyiability. The main upside would be less features when compared to splitting all this up. Also, it would not be very hard to integrate.

Would love to hear everyone's thoughts.

Previous discussions

We have also talked about explicitly excluding certain dependencies from environments. However, @baszalmstra and myself feel this would open a can of worms. Seeing as how long it's taking to even agree on how to exclude the default-feature: #1092 this approach mentioned above would be easier and already supported by the pypi ecosystem.

This kind of leaves the same question for conda dependencies, but I think we might need to tackle this differently, although a similar feature would probably be desirable.