utils/rubocop: activate installed platform Rubydex gem

[p-linnane]

Library/Homebrew/vendor/bundle/bundler/setup.rb is committed and was generated on macOS arm64, so it hardcodes gems/rubydex-0.3.0-arm64-darwin/lib. Other platforms install a different build (Linux aarch64 gets rubydex-0.3.0-aarch64-linux), that path does not exist, and require "rubydex" fails. Library/.rubocop.yml sets AllCops/UseProjectIndex: true, so RuboCop skips the project index and the cops that use it fall back to file-local behavior. brew style is weaker off macOS arm64.

To reproduce, run brew style on Linux and note AllCops/UseProjectIndex is enabled but the rubydex gem is not installed on stderr.

This activates the installed Rubydex specification through RubyGems before RuboCop loads, and only when its require path is missing from $LOAD_PATH. RubyGems filters by platform, so it picks the build that is installed rather than the one baked into the standalone bundle. On macOS arm64 the guard is a no-op, and a missing gem still falls back to RuboCop's existing behavior. The new spec drops Rubydex from $LOAD_PATH and requires rubocop -V to report +Rubydex.

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• I did not use AI/LLM to create this PR, or I disclosed the tool/model below and reviewed its output; I did not attribute commits to AI and will answer maintainer questions and review comments myself without AI/LLM.

Claude Code (Opus 5) drafted the implementation and tests; I reviewed the diff, verified the new test fails without the fix and passes with it, and ran brew lgtm plus targeted specs.

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[MikeMcQuaid]

Good catch!

[Copilot]

Pull request overview

This pull request fixes brew style on non-macOS-arm64 platforms by ensuring the platform-appropriate rubydex gem is activated before RuboCop loads, despite a vendored bundler/setup.rb that hardcodes a macOS arm64 Rubydex load path.

Changes:

• Activate the installed platform-specific rubydex gem (when its require paths are not already present on $LOAD_PATH) before requiring RuboCop.
• Add a spec that simulates a missing Rubydex load path and asserts rubocop -V reports +Rubydex.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
Library/Homebrew/utils/rubocop.rb	Activates the installed platform-specific Rubydex gem before RuboCop loads.
Library/Homebrew/test/rubocop_spec.rb	Adds a regression test to ensure Rubydex is loaded from the installed platform gem outside the Homebrew environment.

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