[p-linnane]

Upgrading a formula that's also a build dependency of another outdated formula could build it from source twice: once as the dependency, then again for its own queued upgrade. The second build reused the same keg, so if it failed it deleted the working installation. The already-attempted check missed the duplicate because the queued installer still held the API-loaded formula while the dependency used the source-loaded one, and Formula#== compares classes.

Compare attempted formulae by full name and spec, as fetch deduplication already does, so the queued upgrade is skipped before its keg is unlinked.

Fixes #24203

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GPT-6 Astra drafted the fix and tests and ran brew lgtm --online; Claude Code (Opus 5.5) reviewed it, reproduced the missed duplicate with real API- and source-loaded formulae and confirmed the regression tests fail without the change and pass with it. I reviewed the diff.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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📥 Commits

Reviewing files that changed from the base of the PR and between 7a8f775 and f387f01.

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📒 Files selected for processing (3)

• Library/Homebrew/formula_installer.rb
• Library/Homebrew/test/formula_installer_spec.rb
• Library/Homebrew/test/install_spec.rb

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🔇 Additional comments (3)

Library/Homebrew/formula_installer.rb (1)

411-411: LGTM!

Also applies to: 1508-1508, 1917-1925

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Library/Homebrew/test/formula_installer_spec.rb (1)

1248-1258: LGTM!

Also applies to: 1260-1265, 1267-1272, 1274-1285

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Library/Homebrew/test/install_spec.rb (1)

124-139: LGTM!

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📝 Summary

Summary by CodeRabbit

• Bug Fixes
  • Prevented duplicate upgrade attempts when the same formula is represented by different formula types.
  • Preserved a keg’s linked state when an upgrade fails after another formula type has already attempted the upgrade.

Walkthrough

FormulaInstaller now identifies equivalent formula attempts by full_name and active_spec_sym, without requiring matching classes. The same comparison is used to locate previously fetched formulas. Tests cover matching boundaries and linked-keg state after a failed upgrade attempt.

Changes

Formula attempt identity

Layer / File(s)	Summary
Formula identity comparison and checks Library/Homebrew/formula_installer.rb	A private comparison matches formulas by full_name and active_spec_sym, regardless of class. Attempt checks and fetched-formula lookup use this comparison.
Attempt-check and upgrade tests Library/Homebrew/test/formula_installer_spec.rb, Library/Homebrew/test/install_spec.rb	Tests cover rejection of matching formulas, allowance for different taps and specs, and linked-keg state after a failed upgrade attempt.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: mikemcquaid

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Merge Risk

Merge Risk: ⚪ Minimal · up to f387f

This change stops an outdated formula from being built from source twice during an upgrade, which could leave its keg broken. No merge-blocking issues were found.

Security Architecture Review

Security architecture risk: ⚪ Minimal · up to f387f

The change prevents duplicate installation attempts while preserving tap and stable/HEAD identity boundaries. No introduced or worsened security risk was identified in the reviewed installation paths.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The reviewed exposure change is broader duplicate suppression for equivalent Formula representations within an installation operation, not a new execution or authority path. Matching still separates different taps and active specs.

Trust Boundaries and Controls

• observed — The installer prelude retains forbidden-license, forbidden-tap and forbidden-formula checks before installation sanity checking. The PR changes duplicate identity recognition rather than removing these controls or adding a privileged caller.

Resilience and Maintainability Implications

• observed — Attempt markers remain recorded before pouring or building, and failed attempts remain subject to operation-local duplicate suppression. Existing dependency restoration, installation locking and exception-time lock release are unchanged; the PR does not introduce a new retry or concurrency mechanism.

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🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: preventing duplicate source upgrades of dependencies.
Description check		The description directly explains the duplicate-build bug, its cause, the fix, regression tests, and validation results.
Linked Issues check		The change satisfies the coding requirement in issue #24203. FormulaInstaller#check_installation_already_attempted now compares full_name and active_spec_sym through same_formula?, so API-load…
Out of Scope Changes check		The changes stay within issue #24203. The helper reuse in previously_fetched_formula applies the same formula identity rule to existing fetch deduplication. The added tests directly verify duplicate…

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[MikeMcQuaid]

Good catch, thanks!