fix(venv): include pth files at the root of the site-packages folder

[aignas]

Before this PR we would not include pth files at the root of the
site-packages folder, but we would include if they are further down
the tree.

Fixes #3339
Fixes #2071

[gemini-code-assist]

Summary of Changes

Hello @aignas, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves an issue where Python .pth files located directly in the site-packages root of a virtual environment were not being included, unlike those in subdirectories. The changes involve updating file extension recognition, refining the virtual environment symlink generation logic to correctly process these top-level files, and adding a dedicated test to ensure their proper inclusion.

Highlights

• .pth file recognition: The build system now explicitly recognizes .pth files by adding them to the PYTHON_FILE_EXTENSIONS list, ensuring they are considered during virtual environment creation.
• Virtual environment symlink generation: The logic for generating virtual environment symlinks has been updated to correctly handle the full path of files, specifically addressing an issue where .pth files at the root of the site-packages directory were previously overlooked.
• Test coverage: A new test case has been introduced to validate that top-level .pth files are properly included when --venvs_site_packages=yes is enabled, confirming the fix and preventing regressions.

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[gemini-code-assist]

Code Review

This pull request fixes an issue where .pth files at the root of site-packages were not correctly included in virtual environments. The fix involves updating the file extension list and modifying how symlink entries are created for root-level files. The changes in the implementation look correct and address the problem. However, the new test case added to verify this fix is flawed, as it asserts an incorrect behavior and doesn't test the new code path. I've provided a detailed comment with a suggested replacement for the test to ensure the fix is properly validated.

[aignas]

/gemini review

[gemini-code-assist]

Code Review

This pull request correctly addresses an issue where .pth files at the root of the site-packages folder were not being included in the virtual environment. The fix involves recognizing .pth as a valid Python file extension and adjusting the symlink creation logic to correctly handle these root-level files. The accompanying test changes effectively validate this fix. I have one suggestion to improve the maintainability of the test code.

[rickeylev]

A functional test would be good, too, but I think its fine for that to be in another PR