[dduugg]

• Stop brew upgrade and brew reinstall relinking kegs that were unlinked with brew unlink, as FormulaInstaller treats link_keg: false as the default for non-keg-only formulae.
• Make link_keg nilable: nil uses the default and false does not link.
• Pass nil from install_dependency unless the dependency was linked, so new dependencies still link.
• Update the formula_installer_spec.rb example that expected link_keg: false to link and add upgrade and reinstall examples for an unlinked keg.
• Reproduce with brew install foo, brew unlink foo and brew reinstall foo (or brew upgrade foo once it is outdated): brew link --dry-run foo then reports Already linked.

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• Have you followed our Contributing guidelines?
• Have you checked for other open Pull Requests for the same change?
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• For bug fixes, have you given step-by-step brew commands to reproduce the bug?
• Have you written new tests (excluding integration tests)? Here's an example.
• Have you successfully run brew lgtm (style, typechecking and tests) locally?

---

• 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 with Sonnet 5.5 and Opus 5.5, with local review and testing.

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[coderabbitai]

Summary

Summary by CodeRabbit

• Bug Fixes
  • Installation, reinstallation and upgrades now preserve an explicit choice to keep a formula unlinked. When no linking choice is specified, the default linking behaviour continues to follow the formula’s eligibility. This keeps the formula’s requested linking state consistent across these installation workflows.

FormulaInstaller now distinguishes an omitted link_keg value from explicit false. During dependency installation, it passes the previous linked state, or nil when that state is false or unavailable. Tests cover initializer defaults and unlinked kegs during reinstall and upgrade.

Changes: Link keg defaults

Layer / File(s)	Summary
Initializer link defaults Library/Homebrew/formula_installer.rb, Library/Homebrew/test/formula_installer_spec.rb	FormulaInstaller#initialize accepts a nullable link_keg value. It derives the default only when the value is nil and preserves explicit false. The spec checks that false remains false.
Dependency link state Library/Homebrew/formula_installer.rb, Library/Homebrew/test/reinstall_spec.rb, Library/Homebrew/test/upgrade_spec.rb	Dependency installation passes the previous linked state, or nil when that state is false or unavailable. Reinstall and upgrade tests check the resulting installer’s link_keg value for an unlinked keg.

Merge Risk: Minimal · previous review 7eefd

Direct upgrades and reinstalls preserve the unlinked state. Unlinked dependencies can still be relinked as before; additional lifecycle tests are recommended.

Pre-merge checks: 4

Check name	Status	Explanation
Title check		The title describes the main change: keeping unlinked kegs unlinked.
Description check		The description covers the linking changes, dependency behaviour, and tests.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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[coderabbitai]

Actionable comments posted: 1

Review info

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Reviewing files that changed from the base of the PR and between 88f401f and c7e5ce3.

Files selected for processing: 4

• Library/Homebrew/formula_installer.rb
• Library/Homebrew/test/formula_installer_spec.rb
• Library/Homebrew/test/reinstall_spec.rb
• Library/Homebrew/test/upgrade_spec.rb

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[MikeMcQuaid]

Thanks looks good! CodeRabbit comment up to you to decide what to do, no rereview needed either way.

[dduugg]

I've corrected the description: !formula.keg_only? || link_keg dates from the 2020 FormulaInstaller refactor, so link_keg: false has been the default for non-keg-only formulae for a long time. (#21684 restored that after #21676, which makes this a behaviour change rather than a fix for a regression.)

[coderabbitai]

Nitpick comments: 2

Library/Homebrew/test/reinstall_spec.rb: 1

23-32: Trivial · Maintainability & Code Quality · Quick win

Test the unlinked state after reinstall.

Run reinstall on a linked, then unlinked, keg. Assert that the opt link remains and that the ordinary prefix links and linked-keg record are absent. The current test only checks the installer flag, so it can pass if the reinstall lifecycle creates ordinary links.

Library/Homebrew/test/upgrade_spec.rb: 1

97-115: Trivial · Maintainability & Code Quality · Quick win

Test the unlinked state after an upgrade.

This test checks the installer flag but does not run the upgrade. A regression in the install or finish path could create ordinary links without failing this test. Add an upgrade test with an older opt-linked, unlinked keg. Assert that the new version is installed and opt-linked, but has no linked-keg record or ordinary prefix links.

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• Library/Homebrew/formula_installer.rb

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