bundle: serialize installs sharing an implicit dependency

[dduugg]

What does this change do, and why?

Addresses one of two independent causes behind #23328 (per @MikeMcQuaid's request for a separate PR per cause).

brew bundle's parallel scheduler (bundle/parallel_installer.rb's build_dependency_map) avoids running two entries in the same batch when their recursive declared dependencies overlap, matching the locking FormulaInstaller#lock does. On Linux, though, formulae can silently gain an implicit dependency at instantiation time (bubblewrap, and gcc/glibc when build formulae are needed) whenever the relevant executable isn't installed yet, added via Formula#add_global_deps_to_spec rather than declared on any formula. Two entries with no declared dependency in common (e.g. bat and xz) can therefore both silently need to fetch the same bottle at once. Since DownloadLock's flock is non-blocking, the loser used to die immediately with OperationInProgressError instead of waiting.

This adds DependencyCollector#implicit_dependency_names, empty by default and overridden on Linux to report whichever of those names would currently be added, and folds it into every entry's recursive dependency set before computing overlaps, so entries that would both need the same implicit dependency get serialized like any other shared dependency.

I wasn't able to fully verify the Linux-specific code path end to end on my own machine (macOS doesn't load extend/os/linux/* at all, confirmed while investigating), so the Linux-specific unit tests here will get their first real execution on Linux CI. Opening as a draft for that reason, please let me know if you'd like anything adjusted before it's ready for a full review.

Step-by-step reproduction

Given in #23328: brew bundle install with a Brewfile containing two formulae that share no declared dependency but would both pull in bubblewrap on a fresh Linux machine without it installed (e.g. bat and xz).

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Used Claude Code to investigate #23328, trace the scheduler's overlap-detection logic and the implicit-dependency mechanism it misses, implement the fix, and write the accompanying tests. Verified by running brew typecheck and brew style --changed (clean), running the full spec files touched (dependency_collector_spec.rb, bundle/installer_spec.rb) and the full bundle directory (all passing), and manually confirming via a scratch script that Formula#recursive_dependencies (no block) preserves :implicit-tagged dependencies rather than pruning them, which the scheduler's overlap check relies on. Reviewed the full diff by hand before opening this PR.

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[MikeMcQuaid]

Thanks! Approach makes sense, just think it's possible to get this information another way instead.

[MikeMcQuaid]

Thanks!

[Copilot]

Pull request overview

This PR updates brew bundle’s parallel scheduler to account for Linux-only implicit formula dependencies (e.g. bubblewrap, gcc, glibc) that can be injected at formula instantiation time, so entries that would contend on the same implicit dependency are scheduled in separate batches to avoid lock/download races.

Changes:

• Add DependencyCollector#implicit_dependency_names to surface currently-applicable implicit dependency formula names.
• Incorporate implicit dependency names into brew bundle’s recursive dependency sets used for overlap/lock-conflict scheduling.
• Add unit tests covering implicit_dependency_names (generic + Linux) and the bundle scheduler’s serialization behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
Library/Homebrew/dependency_collector.rb	Introduces implicit_dependency_names helper to report currently-applicable implicit deps.
Library/Homebrew/bundle/parallel_installer.rb	Adds implicit deps into recursive dependency sets for lock-conflict scheduling in brew bundle.
Library/Homebrew/test/dependency_collector_spec.rb	Verifies default (non-Linux) implicit_dependency_names is empty.
Library/Homebrew/test/os/linux/dependency_collector_spec.rb	Adds Linux-specific tests for bubblewrap/gcc/glibc inclusion in implicit_dependency_names.
Library/Homebrew/test/bundle/installer_spec.rb	Adds a scheduler test ensuring entries are serialized when sharing an implicit dep.

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[MikeMcQuaid]

Yeh, this approach makes more sense I think! Thanks!