Document the interaction of virtualenv with Python interpreter autodetection

[ben-ng]

Description of the problem / feature request / question:

If the bazel server is started when a python virtualenv is activated, actions are run in that virtualenv until the server restarts. bazel clean does not clear this state.

If possible, provide a minimal example to reproduce the problem:

1. Create a python virtualenv
2. Create a python script that imports a dependency in that virtualenv
3. Activate the virtualenv
4. Build & run the script with bazel. It should exit normally.
5. Deactivate the virtualenv. Build & run the script with bazel again. It passes, unexpectedly.
6. bazel shutdown (in practice this happens automatically, which is even more surprising)
7. Build & run the script with bazel. It now fails because the dependency couldn't be found.

It looks like it's because activating the virtualenv changes PATH, and the deactivation of the virtualenv doesn't propagate to the bazel server.

Environment info

• Operating System:

CentOS Linux release 7.0.1406

• Bazel version (output of bazel info release):

release 0.7.0

[brandjon]

Correct me if I'm wrong, but this seems like a natural consequence of how virtualenv works by manipulating the shell env. I suppose we could have the Bazel CLI client check the current shell environment and compare it with the server's state...

I'd consider this a feature request but we can certainly document this behavior regardless.

[brandjon]

FWIW, this issue can be avoided by specifying a py_runtime to refer to an interpreter by a fixed absolute path instead of relying on a command lookup in PATH. This will be more mainstream when #7375 is implemented, though it sounds like the default toolchain (which will look up a runtime from PATH) will still be affected by this issue.

[github-actions]

Thank you for contributing to the Bazel repository! This issue has been marked as stale since it has not had any activity in the last 1+ years. It will be closed in the next 90 days unless any other activity occurs. If you think this issue is still relevant and should stay open, please post any comment here and the issue will no longer be marked as stale.

[github-actions]

This issue has been automatically closed due to inactivity. If you're still interested in pursuing this, please post @bazelbuild/triage in a comment here and we'll take a look. Thanks!