fix(py_venv): Activate embedded interpreters

[arrdem]

Previously the bin/activate script relied on Bazel (specifically bazel run) defined envvars, or being sourced directly from the binary entrypoint. This meant that if the user created a link (eg via the venv link verb or manually) to the venv defined by a given target, sourcing that venv's activate script would fail to locate a runfiles-based interpreter. On systems where there is no appropriately versioned non-hermetic interpreter available, this meant that venvs which should run with the Bazel-managed interpreter instead failed.

The fix is to harden venv initialization so that if the activate script is directly used AND the runfiles preconditions are not met an effort will be made to satisfy them.

---

Changes are visible to end-users: yes

• Searched for relevant documentation and updated as needed: no
• Breaking change (forces users to change their own code or config): no
• Suggested release notes appear below: no

Test plan

• Updated script works on BASH

$ /bin/bash
$ bazel run //examples/py_binary:py_binary.venv
INFO: Analyzed target //examples/py_binary:py_binary.venv (0 packages loaded, 0 targets configured).
INFO: Found 1 target...
Target //examples/py_binary:py_binary.venv up-to-date:
  bazel-bin/examples/py_binary/py_binary.venv
INFO: Elapsed time: 1.224s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
INFO: Running command line: bazel-bin/examples/py_binary/py_binary.venv
Linking: /private/var/tmp/_bazel_arrdem/93bfea6cdc1153cc29a75400cd38823a/execroot/aspect_rules_py/bazel-out/darwin_arm64-fastbuild/bin/examples/py_binary/.py_binary.venv -> /Users/arrdem/Documents/work/aspect/rules_py/.py_binary.venv

To activate the virtualenv run:
    source /Users/arrdem/Documents/work/aspect/rules_py/.py_binary.venv/bin/activate

Link is up to date!
$ ( source .py_binary.venv/bin/activate; echo $VIRTUAL_ENV; which python; which python3; echo $PYTHONHOME; deactivate; echo $VIRTUAL_ENV; which python; which python3 )
/private/var/tmp/_bazel_arrdem/93bfea6cdc1153cc29a75400cd38823a/execroot/aspect_rules_py/bazel-out/darwin_arm64-fastbuild/bin/examples/py_binary/.py_binary.venv
/private/var/tmp/_bazel_arrdem/93bfea6cdc1153cc29a75400cd38823a/execroot/aspect_rules_py/bazel-out/darwin_arm64-fastbuild/bin/examples/py_binary/.py_binary.venv/bin/python
/private/var/tmp/_bazel_arrdem/93bfea6cdc1153cc29a75400cd38823a/execroot/aspect_rules_py/bazel-out/darwin_arm64-fastbuild/bin/examples/py_binary/.py_binary.venv/bin/python3
/private/var/tmp/_bazel_arrdem/93bfea6cdc1153cc29a75400cd38823a/external/python_toolchain_aarch64-apple-darwin

/Users/arrdem/.local/pyenv/shims/python
/Users/arrdem/.local/pyenv/shims/python3

• Updated script works on ZSH

$ /bin/zsh
$ bazel run //examples/py_binary:py_binary.venv
INFO: Analyzed target //examples/py_binary:py_binary.venv (0 packages loaded, 0 targets configured).
INFO: Found 1 target...
Target //examples/py_binary:py_binary.venv up-to-date:
  bazel-bin/examples/py_binary/py_binary.venv
INFO: Elapsed time: 1.224s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
INFO: Running command line: bazel-bin/examples/py_binary/py_binary.venv
Linking: /private/var/tmp/_bazel_arrdem/93bfea6cdc1153cc29a75400cd38823a/execroot/aspect_rules_py/bazel-out/darwin_arm64-fastbuild/bin/examples/py_binary/.py_binary.venv -> /Users/arrdem/Documents/work/aspect/rules_py/.py_binary.venv

To activate the virtualenv run:
    source /Users/arrdem/Documents/work/aspect/rules_py/.py_binary.venv/bin/activate

Link is up to date!
$ ( source .py_binary.venv/bin/activate; echo $VIRTUAL_ENV; which python; which python3; echo $PYTHONHOME; deactivate; echo $VIRTUAL_ENV; which python; which python3 )
/private/var/tmp/_bazel_arrdem/93bfea6cdc1153cc29a75400cd38823a/execroot/aspect_rules_py/bazel-out/darwin_arm64-fastbuild/bin/examples/py_binary/.py_binary.venv
/private/var/tmp/_bazel_arrdem/93bfea6cdc1153cc29a75400cd38823a/execroot/aspect_rules_py/bazel-out/darwin_arm64-fastbuild/bin/examples/py_binary/.py_binary.venv/bin/python
/private/var/tmp/_bazel_arrdem/93bfea6cdc1153cc29a75400cd38823a/execroot/aspect_rules_py/bazel-out/darwin_arm64-fastbuild/bin/examples/py_binary/.py_binary.venv/bin/python3
/private/var/tmp/_bazel_arrdem/93bfea6cdc1153cc29a75400cd38823a/external/python_toolchain_aarch64-apple-darwin

/Users/arrdem/.local/pyenv/shims/python
/Users/arrdem/.local/pyenv/shims/python3

[aspect-workflows]

Test

19 test targets passed

Targets

//examples/multi_version:py_version_default_test [k8-fastbuild]                             1s
//examples/multi_version:py_version_test [k8-fastbuild-ST-494921797612]                     1s
//examples/pytest:pytest_test [k8-fastbuild]                                                2s
//examples/pytest:sharded/test [k8-fastbuild]                                               3s
//examples/virtual_deps:pytest_test [k8-fastbuild]                                          1s
//py/tests/cc-deps:test_smoke [k8-fastbuild]                                                428ms
//py/tests/external-deps:test_can_import_runfiles_helper [k8-fastbuild]                     552ms
//py/tests/internal-deps:assert [k8-fastbuild]                                              999ms
//py/tests/py-binary:runfiles_from_pip_test [k8-fastbuild]                                  1s
//py/tests/py-external-venv:test [k8-fastbuild]                                             190ms
//py/tests/py-internal-venv:test [k8-fastbuild]                                             202ms
//py/tests/py-test:test_env_vars [k8-fastbuild]                                             418ms
//py/tests/py_image_layer:py_image_test [k8-fastbuild]                                      1s
//py/tests/py_venv_image_layer:my_app_amd64_layers_test_test [k8-fastbuild]                 46ms
//py/tests/py_venv_image_layer:my_app_arm64_layers_test_test [k8-fastbuild]                 42ms
//py/tests/py_venv_image_layer:py_amd64_image_command_test [k8-fastbuild]                   998ms
//py/tests/py_venv_image_layer:py_amd64_image_content_test [k8-fastbuild]                   204ms
//py/tests/py_venv_image_layer:py_arm64_image_content_test [k8-fastbuild]                   701ms
//py/tests/repo_relative_imports/test:test [k8-fastbuild]                                   421ms

Total test execution time was 16s. 19 tests (50.0%) were fully cached saving 46s.

[github-actions]

e2e/use_release folder: LCOV of commit a4c3dbd during CI #1816

Summary coverage rate:
  lines......: 100.0% (2 of 2 lines)
  functions..: 100.0% (1 of 1 function)
  branches...: no data found

Files changed coverage rate: n/a

[alexeagle]

🌮