rubocop: check for closed issues in comments

Library/Homebrew/formula_auditor.rb

@@ -816,6 +816,26 @@ module Homebrew
       end
     end
 
+    def audit_github_issue_comment
+      return unless @online
+
+      matches = text.to_s.scan(%r{https://github.com/([-\w_]*)/([-\w_]*)/(pull|issues)/([0-9]*)})
+      return unless matches
+
+      matches.each do |match|
+        owner, repo, type, id = match
+
+        # Do not trigger for self references
+        next if "#{owner}/#{repo}" == formula.tap.remote_repo || owner == "Homebrew"
+
+        issue = GitHub::API.open_rest("https://api.github.com/repos/#{owner}/#{repo}/issues/#{id}")
+        next if issue.blank? || issue["state"] == "open"
+
+        issue_url = "https://github.com/#{owner}/#{repo}/#{type}/#{id}"
+        problem "Formula refers to a GitHub issue or pull request that is closed: #{issue_url}"
+      end
+    end
+
     def audit_reverse_migration
       # Only enforce for new formula being re-added to core
       return unless @strict

Library/Homebrew/formula_text_auditor.rb

@@ -27,6 +27,10 @@ module Homebrew
       @text.include? s
     end
 
+    def to_s
+      @text
+    end
+
     def line_number(regex, skip = 0)
       index = @lines.drop(skip).index { |line| line =~ regex }
       index ? index + 1 : nil