Resolve relative symlinks in bootstrap script

[mattyclarkson]

Currently, the bootstrap script only accepts absolute symlinks.

Implements a patch to resolve relative symlinks.

Adds an extra, take it if you want it, patch that adds an explicit error when a symlink is dangling.

[gemini-code-assist]

Summary of Changes

Hello @mattyclarkson, 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 enhances the robustness of the bootstrap script by improving its symlink resolution capabilities. It ensures that both absolute and relative symlinks are correctly followed, preventing issues that arose from relative paths. Additionally, it introduces a more informative error handling mechanism for broken or dangling symlinks, making the script more resilient and easier to debug.

Highlights

• Relative Symlink Resolution: The bootstrap script has been updated to correctly resolve relative symbolic links, addressing a previous limitation where it only handled absolute symlinks.
• Dangling Symlink Detection: An explicit check has been added to detect and report dangling symbolic links, providing a clear error message when a symlink points to a non-existent target.

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[gemini-code-assist]

Code Review

This pull request correctly identifies and fixes an issue with handling relative symlinks in the bootstrap script. The addition of a check for dangling symlinks is also a valuable improvement. However, I've found a critical bug in the implementation for absolute symlinks where an undefined variable is used. Please see my comment for the fix.

[aignas]

Thanks for providing a patch! We are about to cut a release, so maybe we should wait until after the release branch is created.

Could you add some extra explanation as to what made you add this change? How do you manage python?

[mattyclarkson]

Could you add some extra explanation as to what made you add this change?

During an action, a tool symlinks to a py_binary target with a relative symlink path. This then results in a Unable to find runfiles error as the relative symlink is not resolved. The tool performs relative symlinks because outside of Bazel this will result in a relocatable set of symlinks.

How do you manage python?

We let Bazel manage it with @rules_python//python/config_settings:bootstrap_impl=script.

[aignas]

It would be nice to add some integration tests which would make the change more explanatory and avoid us running into the problem later.