Tox: Cannot substitute install_command from another section (regression in 3.21.0)

[vytas7]

Consider the following tox.ini in an otherwise empty directory:

[tox]
envlist = py38
skipsdist = True

[base]
install_command = python -m pip install {opts} {packages}

[testenv]
install_command = {[base]install_command}
commands =
    python -c 'print("Hi there ;-)")'

$ tox --version
3.21.0 imported from /tmp/venv/lib/python3.8/site-packages/tox/__init__.py

Observed result

Cannot substitute install_command from the [base] section:

$ tox -rvv
using tox.ini: /tmp/test/tox.ini (pid 8575)
  removing /tmp/test/.tox/log
Traceback (most recent call last):
  File "/tmp/venv/bin/tox", line 8, in <module>
    sys.exit(cmdline())
  File "/tmp/venv/lib/python3.8/site-packages/tox/session/__init__.py", line 44, in cmdline
    main(args)
  File "/tmp/venv/lib/python3.8/site-packages/tox/session/__init__.py", line 65, in main
    config = load_config(args)
  File "/tmp/venv/lib/python3.8/site-packages/tox/session/__init__.py", line 81, in load_config
    config = parseconfig(args)
  File "/tmp/venv/lib/python3.8/site-packages/tox/config/__init__.py", line 280, in parseconfig
    ParseIni(config, config_file, content)
  File "/tmp/venv/lib/python3.8/site-packages/tox/config/__init__.py", line 1276, in __init__
    raise tox.exception.ConfigError(
tox.exception.ConfigError: ConfigError: py38 failed with ConfigError: substitution key 'opts' not found at Traceback (most recent call last):
  File "/tmp/venv/lib/python3.8/site-packages/tox/config/__init__.py", line 1252, in run
    results[name] = cur_self.make_envconfig(name, section, subs, config)
  File "/tmp/venv/lib/python3.8/site-packages/tox/config/__init__.py", line 1407, in make_envconfig
    res = meth(env_attr.name, env_attr.default, replace=replace)
  File "/tmp/venv/lib/python3.8/site-packages/tox/config/__init__.py", line 1716, in getargv_install_command
    return _ArgvlistReader.getargvlist(self, s, replace=replace, name=name)[0]
  File "/tmp/venv/lib/python3.8/site-packages/tox/config/__init__.py", line 1946, in getargvlist
    commands.extend(cls.getargvlist(reader, replaced, name=name))
  File "/tmp/venv/lib/python3.8/site-packages/tox/config/__init__.py", line 1948, in getargvlist
    commands.append(cls.processcommand(reader, current_command, replace, name=name))
  File "/tmp/venv/lib/python3.8/site-packages/tox/config/__init__.py", line 1974, in processcommand
    new_word = reader._replace(word, name=name)
  File "/tmp/venv/lib/python3.8/site-packages/tox/config/__init__.py", line 1782, in _replace
    replaced = Replacer(self, crossonly=crossonly).do_replace(value)
  File "/tmp/venv/lib/python3.8/site-packages/tox/config/__init__.py", line 1818, in do_replace
    expanded = substitute_once(value)
  File "/tmp/venv/lib/python3.8/site-packages/tox/config/__init__.py", line 1816, in substitute_once
    return self.RE_ITEM_REF.sub(self._replace_match, x)
  File "/tmp/venv/lib/python3.8/site-packages/tox/config/__init__.py", line 1876, in _replace_match
    return self._replace_substitution(sub_value)
  File "/tmp/venv/lib/python3.8/site-packages/tox/config/__init__.py", line 1911, in _replace_substitution
    val = self._substitute_from_other_section(sub_key)
  File "/tmp/venv/lib/python3.8/site-packages/tox/config/__init__.py", line 1906, in _substitute_from_other_section
    raise tox.exception.ConfigError("substitution key {!r} not found".format(key))
tox.exception.ConfigError: ConfigError: substitution key 'opts' not found

Expected result

$ tox --version
3.20.1 imported from /tmp/venv/lib/python3.8/site-packages/tox/__init__.py

$ tox -r
py38 recreate: /tmp/test/.tox/py38
py38 run-test-pre: PYTHONHASHSEED='1073641419'
py38 run-test: commands[0] | python -c 'print("Hi there ;-)")'
Hi there ;-)
___________________________________________________________________________ summary ____________________________________________________________________________
  py38: commands succeeded
  congratulations :)

[gaborbernat]

Thanks for reporting it, if you have time feel free to open a PR fixing it 👍

[vytas7]

Heh, thanks for the invitation. And thanks for maintaining tox!
But I'm afraid I'm unable to spare the time right now.

[jayvdb]

I'll take a look at this, as it looks like a bug in one of my changes.

[jayvdb]

I've got a fix together - just needs a bit more polish. Will have it up today.

[jayvdb]

@gaborbernat , this should be closed now. Not sure why the commit message didnt auto-close it.

[jayvdb]

Actually it looks like a force push has deleted that commit (da140fb) on master.

[gaborbernat]

Released now via https://tox.readthedocs.io/en/latest/changelog.html#v3-21-1-2021-01-13