autoremove: allow removing source-built formulae - #24471

Minor · Keep build dependencies of source-built formulae that casks require. · autoremove.rb:18-19

Library/Homebrew/utils/autoremove.rb:18-19
Minor · Functional Correctness · Quick win

Keep build dependencies of source-built formulae that casks require.

When HOMEBREW_AUTOREMOVE_BUILT_FROM_SOURCE is set, a source-built formula that a cask requires can still be selected as unused. The recursive pass then removes it from its input, so its build dependencies are no longer protected. The later cask filter keeps that formula. It does not restore protection for its build dependencies. The InstalledDependents check after selection reads runtime dependencies only, so it does not protect build-only edges either.

The installed formula keeps working. A later rebuild from source may fail or require reinstalling the removed build dependency.

Apply the cask check during candidate selection. The protected formula then stays in the input, and its build dependencies stay protected.

Suggested fix

       def removable_formulae(formulae, casks, keep_built_from_source: true)
-        unused_formulae = unused_formulae_with_no_formula_dependents(formulae, keep_built_from_source:)
         cask_dep_names = cask_dependent_formula_names(casks, formulae)
-        unused_formulae.reject { |f| cask_dep_names.intersect?(f.possible_names) }
+        unused_formulae_with_no_formula_dependents(formulae, keep_built_from_source:, protected_names: cask_dep_names)
       end

-      sig { params(formulae: T::Array[Formula], keep_built_from_source: T::Boolean).returns(T::Array[Formula]) }
-      def unused_formulae_with_no_formula_dependents(formulae, keep_built_from_source: true)
+      sig {
+        params(formulae: T::Array[Formula], keep_built_from_source: T::Boolean,
+               protected_names: T::Set[String]).returns(T::Array[Formula])
+      }
+      def unused_formulae_with_no_formula_dependents(formulae, keep_built_from_source: true, protected_names: Set.new)
         unused_formulae = bottled_formulae_with_no_formula_dependents(formulae, keep_built_from_source:).select do |f|
           tab = f.any_installed_keg&.tab
           next unless tab
           next unless tab.installed_on_request_present?
+          next if protected_names.intersect?(f.possible_names)
 
           tab.installed_on_request == false
         end
 
         unless unused_formulae.empty?
-          unused_formulae += unused_formulae_with_no_formula_dependents(formulae - unused_formulae,
-                                                                        keep_built_from_source:)
+          unused_formulae += unused_formulae_with_no_formula_dependents(formulae - unused_formulae,
+                                                                        keep_built_from_source:,
+                                                                        protected_names:)
         end

Minor · Qualify the build-dependency guarantee for… · env_config.rb:107-112

Library/Homebrew/env_config.rb:107-112
Minor · Functional Correctness · Quick win

Qualify the build-dependency guarantee for HOMEBREW_NO_CLEANUP_FORMULAE.

The description says that build dependencies of remaining source-built formulae are kept. That does not hold for formulae listed in HOMEBREW_NO_CLEANUP_FORMULAE, or for their installed runtime dependencies. Autoremove removes those formulae from its input before it selects candidates. Their build dependencies then lose that protection, and they can be removed unless another rule keeps them. Reinstalling a removed source-built build dependency can be slow, which the PR is meant to avoid.

Suggested fix

         description: "If set, `brew autoremove`, `brew cleanup` and `brew uninstall` will also remove unused " \
                      "formulae that were built from source. Build dependencies of the remaining formulae that " \
-                     "were built from source are still kept.",
+                     "were built from source are still kept. This rule does not keep build dependencies of " \
+                     "formulae listed in `HOMEBREW_NO_CLEANUP_FORMULAE`, or of their installed runtime " \
+                     "dependencies. Other rules can still keep them.",
         boolean:     true,

Regenerate manpages/brew.1 and docs/Manpage.md from the same description text. The docs/Manpage.md body was not inspected, so this change is not shown as a diff for that file.