Revert "dependency: don't recurse infinitely."

This reverts commit 16ffbe1a2b2d99da42481dc50f70dbfee4472da6.

Library/Homebrew/dependency.rb

@@ -71,31 +71,25 @@ class Dependency
     # The default filter, which is applied when a block is not given, omits
     # optionals and recommendeds based on what the dependent has asked for.
     def expand(dependent, deps = dependent.deps, &block)
-      # Keep track dependencies to avoid infinite cyclic dependency recursion.
-      @expand_stack ||= []
-      @expand_stack.push dependent.name
-
       expanded_deps = []
 
       deps.each do |dep|
+        # FIXME: don't hide cyclic dependencies
         next if dependent.name == dep.name
 
         case action(dependent, dep, &block)
         when :prune
           next
         when :skip
-          next if @expand_stack.include? dep.name
           expanded_deps.concat(expand(dep.to_formula, &block))
         when :keep_but_prune_recursive_deps
           expanded_deps << dep
         else
-          next if @expand_stack.include? dep.name
           expanded_deps.concat(expand(dep.to_formula, &block))
           expanded_deps << dep
         end
       end
 
-      @expand_stack.pop
       merge_repeats(expanded_deps)
     end