cache DeclarativePolicy.class_for at the class level

lib/declarative_policy.rb

@@ -8,7 +8,12 @@ require_dependency 'declarative_policy/step'
 
 require_dependency 'declarative_policy/base'
 
+require 'thread'
+
 module DeclarativePolicy
+  CLASS_CACHE_MUTEX = Mutex.new
+  CLASS_CACHE_IVAR = :@__DeclarativePolicy_CLASS_CACHE
+
   class << self
     def policy_for(user, subject, opts = {})
       cache = opts[:cache] || {}
@@ -23,7 +28,36 @@ module DeclarativePolicy
 
       subject = find_delegate(subject)
 
-      subject.class.ancestors.each do |klass|
+      class_for_class(subject.class)
+    end
+
+    private
+
+    # This method is heavily cached because there are a lot of anonymous
+    # modules in play in a typical rails app, and #name performs quite
+    # slowly for anonymous classes and modules.
+    #
+    # See https://bugs.ruby-lang.org/issues/11119
+    #
+    # if the above bug is resolved, this caching could likely be removed.
+    def class_for_class(subject_class)
+      unless subject_class.instance_variable_defined?(CLASS_CACHE_IVAR)
+        CLASS_CACHE_MUTEX.synchronize do
+          # re-check in case of a race
+          break if subject_class.instance_variable_defined?(CLASS_CACHE_IVAR)
+
+          policy_class = compute_class_for_class(subject_class)
+          subject_class.instance_variable_set(CLASS_CACHE_IVAR, policy_class)
+        end
+      end
+
+      policy_class = subject_class.instance_variable_get(CLASS_CACHE_IVAR)
+      raise "no policy for #{subject.class.name}" if policy_class.nil?
+      policy_class
+    end
+
+    def compute_class_for_class(subject_class)
+      subject_class.ancestors.each do |klass|
         next unless klass.name
 
         begin
@@ -37,12 +71,8 @@ module DeclarativePolicy
           nil
         end
       end
-
-      raise "no policy for #{subject.class.name}"
     end
 
-    private
-
     def find_delegate(subject)
       seen = Set.new