Ensure tox_extend_envs list can be read twice
#3598
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Previously (PR tox-dev#3591) a new hook point was added. The tests checked that it works well with the `tox config` and `tox list` commands. However, `tox run` turned out to have a problem — it would complain that there's no such env, when invoked: ```console ROOT: 170 E HandledError| provided environments not found in configuration file: pip-compile-tox-env-lock [tox/run.py:23] ``` Turned out, this was because the config object is being interated twice in some subcommands. This in turn iterates over the discovered additional ephemeral environments list object. The implementation passes an iterator into it and so when it's first accessed, it's exhausted and the second attempt does not give the same envs, causing inconsistency. The patch solves this by using `itertools.tee()`, making sure that the underlying iterable is always cached and it's possible to repeat iteration as many times as possible without loosing the data in the process.
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Urgh.. it looks like the fix doesn't work on older Pythons (3.11 and lower). I'll take a look. |
Before Python 3.11, the first value is the the underlying iterator. And we still exhaust it. So for backwards compatibility, we request two iterators and disregard the first one.
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@gaborbernat this is now ready for inclusion in v4.29.1 |
gaborbernat
approved these changes
Sep 2, 2025
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@gaborbernat could you release when you have time? |
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Previously (PR #3591) a new hook point was added. The tests checked that it works well with the
tox configandtox listcommands. However,tox runturned out to have a problem — it would complain that there's no such env, when invoked:Turned out, this was because the config object is being interated twice in some subcommands. This in turn iterates over the discovered additional ephemeral environments list object. The implementation passes an iterator into it and so when it's first accessed, it's exhausted and the second attempt does not give the same envs, causing inconsistency.
The patch solves this by using
itertools.tee(), making sure that the underlying iterable is always cached and it's possible to repeat iteration as many times as possible without loosing the data in the process.tox -e fix)docs/changelogfolder