Experiment: "deselecting" default dependencies using extras

[abravalheri]

This is an experiment to test the waters regarding the possibility discussed in pypa/setuptools#4457 (comment):

Yeah, I bemoan these transitive dependencies too. I would like to refactor some of these supporting libraries so that they have fewer unused dependencies (as inflect and autocommand are in many cases). This problem would be easier if packages could have "default extras" that could be deselected on install (or vendoring).

Although we don't yet have the concept of "default" extras in Python, we can implement "exclusion" extras with an environment marker: dependency==0.42; extra != "xyz".

This does however mean that the code has to be written in a way that it allows for the "deselected dependency" to lazily evaluated or not evaluated at all. When the import statement resides in an isolated submodule that is easy and does not require many changes. However if the import statement is in __init__.py or in a submodule that is imported in other parts of the codebase, things start to be more complicated.

The reason why I decided to try the experiment with jaraco.text is because it seems to be the dependency of setuptools that brings most transient dependencies with itself. According to pipdeptree:

importlib_metadata==8.2.0
  zipp==3.20.0
jaraco.text==4.0.0
  autocommand==2.2.2
  importlib_resources==6.4.2
    zipp==3.20.0
  jaraco.context==5.3.0
    backports.tarfile==1.2.0
  jaraco.functools==4.0.2
    more-itertools==10.4.0
  more-itertools==10.4.0
ordered-set==4.1.0
packaging==24.1
platformdirs==4.2.2
tomli==2.0.1
wheel==0.44.0

This PR is by no means exhaustive, I only implemented the 2 most obvious optional exclusions to me.

[abravalheri]

I added this comment here to help clarifying to the end-user reading the docstring where is the files function coming from.

[Avasam]

If this solution is found acceptable (I think the main point of difference here being that it's for a temporary backport). Would a similar approach be applicable for jaraco.context's backports.tarfile? (see rejected #15 )

[abravalheri]

I did some tests and I was under the impression that the extra != ... marker works. I even remember seeing the output of pip list. But I was wrong and my memories deceiving.

extra != ... does not work, as explained in pypa/pip#8686 (comment).