Revert "Revert "dependency: don't recurse infinitely.""

This reverts commit fa43883dd1cd82f234b79c4a322339f03b9c098d.

Closes Homebrew/homebrew#48187.

Library/Homebrew/dependency.rb

@@ -71,25 +71,31 @@ 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
 

Library/Homebrew/test/test_dependency_expansion.rb

@@ -73,7 +73,7 @@ class DependencyExpansionTests < Homebrew::TestCase
   def test_merger_preserves_env_proc
     env_proc = stub
     dep = Dependency.new("foo", [], env_proc)
-    dep.stubs(:to_formula).returns(stub(:deps => []))
+    dep.stubs(:to_formula).returns(stub(:deps => [], :name => "foo"))
     @deps.replace [dep]
     assert_equal env_proc, Dependency.expand(@f).first.env_proc
   end