Move code to external mkdocs-get-deps dependency

[oprypin]

The "get-deps" command will still be provided inside MkDocs like before (and is not deprecated at all) but is now implemented in a separate repository and can be used directly from there as well.
https://github.com/mkdocs/get-deps

This separation of code was done because obtaining just the "get-deps" part with very few dependencies can be useful: one can run it in a main environment but then install actual MkDocs with dependencies in a virtual environment.

I have also already applied this extracted small library "mkdocs-get-deps" for another use case, which I'm very proud of:

https://github.com/mkdocs/hatch-mkdocs 🆕

In the near future I will write a new recommended guide for how to manage dependencies for a MkDocs site. This is only one part of it though.

[sillydan1]

This creates a problem with pip<=22.0.2 (the version shipped with ubuntu:22.04 is 22.0.2)

Upgrading the pip version to pip>=22.0.3 fixes the issue.

Recreation requirements.txt:

mkdocs
mkdocs-material

Recreation steps:

Launch a new ubuntu 22.04 container:

docker run --rm -it -v .:/code -w /code ubuntu:22.04

Inside the container

apt update
apt install python3 python3-pip
python3 -m pip install mkdocs mkdocs-material

Observe that pypa/pip#10851 occurs

[pawamoy]

Hi @sillydan1, I'm not sure to understand why this resolved pip bug from 2022 is relevant to this PR.

[oprypin]

Thanks for the report @sillydan1 . It should probably be opened as a new issue.

@pawamoy The problem, as was already described, is that users of Ubuntu 22.04 out of the box get an error for this command:

pip install mkdocs mkdocs-material

I confirm the finding, this was my repro:

virtualenv venv
venv/bin/pip install pip==22.0.2
venv/bin/pip install mkdocs mkdocs-material

Error:

ERROR: Exception:
Traceback (most recent call last):
  File "/tmp/a/venv/lib/python3.11/site-packages/pip/_internal/cli/base_command.py", line 165, in exc_logging_wrapper
    status = run_func(*args)
             ^^^^^^^^^^^^^^^
  File "/tmp/a/venv/lib/python3.11/site-packages/pip/_internal/cli/req_command.py", line 205, in wrapper
    return func(self, options, args)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/a/venv/lib/python3.11/site-packages/pip/_internal/commands/install.py", line 389, in run
    to_install = resolver.get_installation_order(requirement_set)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/a/venv/lib/python3.11/site-packages/pip/_internal/resolution/resolvelib/resolver.py", line 188, in get_installation_order
    weights = get_topological_weights(
              ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/a/venv/lib/python3.11/site-packages/pip/_internal/resolution/resolvelib/resolver.py", line 276, in get_topological_weights
    assert len(weights) == expected_node_count
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError

The cause is the intersection of the bug in pip and the fact that mkdocs-material pinned the version of MkDocs.

https://github.com/squidfunk/mkdocs-material/blob/5f40a5337492c8e8578142bd39b29d938af73947/requirements.txt#L24

The best solution would be to unpin versions there. In the world of Python packaging, it is hostile to pin versions in a library, because it just doesn't work well. See my comment that I wrote for a different project:

• Please remove dependency pinning, at least for MkDocs Guts/mkdocs-rss-plugin#137 (comment)

Some workarounds in the meantime

1. pip install -U pip

2. pip install 'mkdocs' 'mkdocs-material<=9.5.2'

3. pip install 'mkdocs<=1.5.3' 'mkdocs-material'

[oprypin]

Also @sillydan1 I'm not sure how you determined that this PR causes it. I was not able to confirm or deny that, but I think it's not related. I think the bug is purely due to the version number conflict. In any case definitely should be a separate issue.

[sillydan1]

Sorry for reviving a closed PR. You're right, this should be an issue by itself - I will create one.

I'm not sure how you determined that this PR causes it.

The only changes that happened to my CI build was that mkdocs was upgraded to v1.6.0 and that mkdocs-get-deps would be installed as a consequence. In retrospect, it's just a red herring and the issue you mentioned @oprypin with mkdocs-material version pinning is the root cause.

EDIT: Nevermind, someone beat me to it