Fix Tox configuration issue

[agjohnson]

I was getting errors from Tox about base_path replacement not
existing. This was using inv docker.test, so I don't think this is
limited to me.

inv docker.test -a "-e py310 -- -k ProjectsEndpointTests"             
Traceback (most recent call last):
  File "/usr/local/bin/tox", line 8, in <module>
    sys.exit(cmdline())
  File "/usr/local/lib/python3.10/dist-packages/tox/session/__init__.py", line 44, in cmdline
    main(args)
  File "/usr/local/lib/python3.10/dist-packages/tox/session/__init__.py", line 65, in main
    config = load_config(args)
  File "/usr/local/lib/python3.10/dist-packages/tox/session/__init__.py", line 81, in load_config
    config = parseconfig(args)
  File "/usr/local/lib/python3.10/dist-packages/tox/config/__init__.py", line 299, in parseconfig
    ParseIni(config, config_file, content)
  File "/usr/local/lib/python3.10/dist-packages/tox/config/__init__.py", line 1323, in __init__
    raise tox.exception.ConfigError(
tox.exception.ConfigError: ConfigError: migrations failed with ConfigError: substitution key 'base_python' not found at Traceback (most recent call last):
  File "/usr/local/lib/python3.10/dist-packages/tox/config/__init__.py", line 1299, in run
    results[name] = cur_self.make_envconfig(name, section, subs, config)
  File "/usr/local/lib/python3.10/dist-packages/tox/config/__init__.py", line 1475, in make_envconfig
    res = meth(env_attr.name, env_attr.default, replace=replace)
  File "/usr/local/lib/python3.10/dist-packages/tox/config/__init__.py", line 1772, in getargvlist
    return _ArgvlistReader.getargvlist(self, s, replace=replace, name=name)
  File "/usr/local/lib/python3.10/dist-packages/tox/config/__init__.py", line 2036, in getargvlist
    commands.append(cls.processcommand(reader, current_command, replace, name=name))
  File "/usr/local/lib/python3.10/dist-packages/tox/config/__init__.py", line 2062, in processcommand
    new_word = reader._replace(word, name=name)
  File "/usr/local/lib/python3.10/dist-packages/tox/config/__init__.py", line 1857, in _replace
    replaced = Replacer(self, crossonly=crossonly).do_replace(value)
  File "/usr/local/lib/python3.10/dist-packages/tox/config/__init__.py", line 1893, in do_replace
    expanded = substitute_once(value)
  File "/usr/local/lib/python3.10/dist-packages/tox/config/__init__.py", line 1891, in substitute_once
    return self.RE_ITEM_REF.sub(self._replace_match, x)
  File "/usr/local/lib/python3.10/dist-packages/tox/config/__init__.py", line 1964, in _replace_match
    return self._replace_substitution(sub_value)
  File "/usr/local/lib/python3.10/dist-packages/tox/config/__init__.py", line 1999, in _replace_substitution
    val = self._substitute_from_other_section(sub_key)
  File "/usr/local/lib/python3.10/dist-packages/tox/config/__init__.py", line 1994, in _substitute_from_other_section
    raise tox.exception.ConfigError("substitution key {!r} not found".format(key))
tox.exception.ConfigError: ConfigError: substitution key 'base_python' not found

[humitos]

I don't think this is
limited to me.

Yeah, I've also got this errors. However, I didn't debug it 😅 . I suppose your PR is fine 👍🏼

[benjaoming]

This sounds like another fall-out of the Tox 4 upgrade. I don't think it seems very well documented. In general, it seems like a lot of substitution variables with underscores _ have the underscore as an option but that the version without the underscore is the "main" documented variable name.

The Tox documentation does, however, still casually mention the "aliases" with underscores around in their docs.

https://tox.wiki/en/latest/config.html#python-options

https://tox.wiki/en/latest/faq.html#new-features-in-tox-4

It could appear like the base_python isn't set automatically anymore from the environment, but only basepython is... even though base_python is documented to resolve the same way.

[benjaoming]

What made me suspicious that it's a Tox 4 regression is this entry in the release FAQ:

basepython is now a list, the first successfully detected python will be used to generate python environment.

[stsewd]

Also, weird that this works on our CI, guess the update that @benjaoming mentioned, or you may need to rebuild your docker env to install the latest version of tox.

[agjohnson]

or you may need to rebuild your docker env to install the latest version of tox.

These tests were in Docker, via inv docker.test, so it should be up to date, no?

[stsewd]

These tests were in Docker, via inv docker.test, so it should be up to date, no?

That command makes use of the web container, after requirements are updated, you need to run inv docker.build. I run the command without this patch and it worked.

root@191d3c567ae8:/usr/src/app/checkouts/readthedocs.org# tox --version
4.0.14 from /usr/local/lib/python3.10/dist-packages/tox/__init__.py

[agjohnson]

Confirmed, another rebuild does resolve the issue, without this PR.

I came across this in #9843, where I needed to docker.build no less than 5 times to get my environment working, so not sure why this was missing.