audit: unnecessary comments from external taps

Co-Authored-By: Mike McQuaid <mike@mikemcquaid.com>

Library/Homebrew/rubocops/lines.rb

@@ -64,6 +64,15 @@ module RuboCop
 
             problem "Commented-out dependency #{Regexp.last_match(1)}"
           end
+
+          return if formula_tap != "homebrew-core"
+
+          # Citation and tag comments from third-party taps
+          audit_comments do |comment|
+            next if comment !~ /#\s*(cite(?=\s*\w+:)|doi(?=\s*['"])|tag(?=\s*['"]))/
+
+            problem "Formulae in homebrew/core should not use `#{Regexp.last_match(1)}` comments"
+          end
         end
       end
 

Library/Homebrew/test/rubocops/lines_spec.rb

@@ -106,6 +106,21 @@ describe RuboCop::Cop::FormulaAudit::Comments do
         end
       RUBY
     end
+
+    it "citation tags" do
+      expect_offense(<<~RUBY, "/homebrew-core/")
+        class Foo < Formula
+          desc "foo"
+          url 'https://brew.sh/foo-1.0.tgz'
+          # cite Howell_2009:
+          ^^^^^^^^^^^^^^^^^^^ Formulae in homebrew/core should not use `cite` comments
+          # doi "10.111/222.x"
+          ^^^^^^^^^^^^^^^^^^^^ Formulae in homebrew/core should not use `doi` comments
+          # tag "software"
+          ^^^^^^^^^^^^^^^^ Formulae in homebrew/core should not use `tag` comments
+        end
+      RUBY
+    end
   end
 end