chore: enable pipstar for experimental_index_url users

[aignas]

bazel query may break if users right now rely on the behaviour of:

only host platform packages are present in the whl_library instances

When we enabled pipstar by default, one of our user reported this breakage
because:

1. The triton dependency is only used on linux and it is in one of the
   requirements files.
2. On mac, this dependency did not have a whl_library repository materialized
   and the bazel query failed because of this reason.

Hence we enable pipstar in a different way - we only enable it when whl files
are downloaded via the bazel downloader and bazel query is less likely to fail
if you can use the bazel downloader for all of your deps.

Work towards #2949

[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 introduces a targeted adjustment to how pipstar is enabled within whl_library rules. The primary goal is to enhance the robustness of bazel query operations, particularly in environments with platform-specific dependencies, by ensuring pipstar is active when wheel files are directly managed by Bazel's downloader or provided via labels. This prevents build failures stemming from unmaterialized dependencies on incompatible platforms, streamlining the dependency resolution process for experimental_index_url users.

Highlights

• Pipstar Activation Logic Refinement: The mechanism for enabling pipstar within whl_library has been updated. Previously, it relied on rp_config.enable_pipstar and rctx.attr.config_load. Now, pipstar is explicitly enabled if the wheel file is provided via a whl_path (meaning it's passed through a label or downloaded directly by Bazel), ensuring it's active for these scenarios.
• Improved Cross-Platform Compatibility: This change addresses a specific issue where bazel query could fail on non-Linux platforms (e.g., macOS) if a Linux-specific dependency (like triton) was listed in requirements but its whl_library was not materialized on the current platform. By enabling pipstar more broadly for directly provided/downloaded wheels, this breakage is prevented.
• Changelog Documentation: A new entry has been added to CHANGELOG.md to reflect that pipstar is now enabled for all whl_library instances where the wheel is passed through a label or downloaded using the Bazel downloader, providing clear documentation for users.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[gemini-code-assist]

Code Review

This pull request correctly enables pipstar more selectively to avoid issues with bazel query on platform-specific dependencies. The change enables pipstar for wheels that are provided directly via a label or downloaded with the Bazel downloader, which aligns with the stated goal. The logic is sound, and the changelog is updated accordingly. I've added one suggestion to improve the clarity of the new logic in whl_library.bzl.