tox4: cannot handle empty envlist for tox -l

[jugmac00]

❯ tox4 -l
Traceback (most recent call last):
  File "/home/jugmac00/.local/bin/tox4", line 8, in <module>
    sys.exit(run())
  File "/home/jugmac00/.local/lib/python3.6/site-packages/tox/run.py", line 22, in run
    result = main(sys.argv[1:] if args is None else args)
  File "/home/jugmac00/.local/lib/python3.6/site-packages/tox/run.py", line 47, in main
    result = handler(state)
  File "/home/jugmac00/.local/lib/python3.6/site-packages/tox/session/cmd/legacy.py", line 98, in legacy
    return list_env(state)
  File "/home/jugmac00/.local/lib/python3.6/site-packages/tox/session/cmd/list_env.py", line 27, in list_env
    max_length = max(len(env) for env in (default.envs + extra))
ValueError: max() arg is an empty sequence

reproduction

Just delete the complete content of tox.ini on the rewrite branch.

(I noticed this problem when trying to reproduce #1985)

Interestingly (for me), tox4 list does not crash...

TIL: tox -l and tox list are not aliases => -l and --listenvs are legacy options, and not the same as list

❯ tox4 list
additional environments:
py -> [no description]

(btw what is py??? and why is there an entry, when there is no additional environment)

[jugmac00]

The issue looks straightforward (except for the additional environment: py).

I'd like to work on this one.

[gaborbernat]

Because empty envlist is translated to py extra. That's by design. tox -l should though make it empty 👍🏻 to be backwards compatible.

[jugmac00]

closed by #1988