Add support for exec subcommand

[gaborbernat]

Run arbitrary commands within your tox environment. Don't abuse it.

Resolves #1790

[codecov]

Codecov Report

Merging #2142 (1a54692) into rewrite (62976a9) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           rewrite    #2142   +/-   ##
========================================
  Coverage    99.85%   99.85%           
========================================
  Files          155      157    +2     
  Lines         8693     8744   +51     
  Branches       918      921    +3     
========================================
+ Hits          8680     8731   +51     
  Misses           3        3           
  Partials        10       10           

Flag	Coverage Δ
tests	99.85% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
src/tox/plugin/manager.py	100.00% <100.00%> (ø)
src/tox/session/cmd/devenv.py	100.00% <100.00%> (ø)
src/tox/session/cmd/exec_.py	100.00% <100.00%> (ø)
src/tox/session/common.py	100.00% <100.00%> (ø)
tests/config/cli/conftest.py	100.00% <100.00%> (ø)
tests/session/cmd/test_exec_.py	100.00% <100.00%> (ø)

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[jugmac00]

While there are several potentially dangerous configuration options (e.g. delete directories) already present in tox, this one is special - let's hope for the best 👍

@asottile Any opinion on this one?

I am not super happy with the autogenerated documentation, as at least I could not see that the command needs to be passed in after a double dash --.

Is there anything we could do with the autogenerated docs or maybe should we add a FAQ entry? Although - technically it is not a frequently asked question :-)

[gaborbernat]

I am not super happy with the autogenerated documentation, as at least I could not see that the command needs to be passed in after a double dash --.

It's documented in the epilogue of the sub-command (see tox4 e --help), if it's not rendering means we need to fix that in our documentation generation.

[jugmac00]

I am not super happy with the autogenerated documentation, as at least I could not see that the command needs to be passed in after a double dash --.

It's documented in the epilogue of the sub-command (see tox4 e --help), if it's not rendering means we need to fix that in our documentation generation.

Thanks - tox4 exec --help indeed renders the example - the documentation does not - yet.

[gaborbernat]

Created tox-dev/sphinx-argparse-cli#20 to address that.

[gaborbernat]

While there are several potentially dangerous configuration options (e.g. delete directories) already present in tox, this one is special - let's hope for the best

I don't think it's overly dangerous. Users can already invoke commands within the tox environments (as in .tox/py39/bin/pip install x). The only thing this adds is convenience to easier invocation for that, and allowing you to take advantage of tox environment isolation and altering. And we're all consenting adults here at the end of the day, not?