Improvements on .policy_class support

The `BlogPolicy -> "BlogPolicy" -> "Blog" -> "BlogPolicy" -> BlogPolicy`
issue @jnicklas pointed out has been resolved. For example, given

```ruby
class BlogPolicy < Struct.new(:user, :blog); end
class Blog; end
class ArtificialBlog < Blog
  def self.policy_class
    BlogPolicy
  end
end
```

The above string manipulation/casting is prevented; the `BlogPolicy`
class will be immediately returned to `policy` and on to be evaluated.

Anonymous classes are now supported too. For example, given

```ruby
class BlogPolicy < Struct.new(:user, :blog); end
class Blog; end
class ArtificialBlog < Blog
  def self.policy_class
    Struct.new(:user, :blog) do
      def create?
        true
      end
    end
  end
end
```

The `Struct` will be returned and evaluated as any other policy.

lib/pundit/policy_finder.rb

@@ -6,30 +6,16 @@ module Pundit
       @object = object
     end
 
-    def name
-      if object.respond_to?(:policy_class)
-        object.policy_class.name.gsub(/Policy$/, '')
-      elsif object.class.respond_to?(:policy_class)
-        object.class.policy_class.name.gsub(/Policy$/, '')
-      elsif object.respond_to?(:model_name)
-        object.model_name.to_s
-      elsif object.class.respond_to?(:model_name)
-        object.class.model_name.to_s
-      elsif object.is_a?(Class)
-        object.to_s
-      else
-        object.class.to_s
-      end
-    end
-
     def scope
-      scope_name.constantize
+      policy::Scope
     rescue NameError
       nil
     end
 
     def policy
-      policy_name.constantize
+      klass = policy_evaluator
+      klass = klass.constantize if klass.is_a?(String)
+      klass
     rescue NameError
       nil
     end
@@ -42,12 +28,33 @@ module Pundit
       policy or raise NotDefinedError, "unable to find policy #{policy_name} for #{object}"
     end
 
-    def scope_name
-      "#{name}Policy::Scope"
-    end
+    private
+      def policy_evaluator
+        if object.respond_to?(:policy_class)
+          return object.policy_class
+        elsif object.class.respond_to?(:policy_class)
+          return object.class.policy_class
+        elsif object.respond_to?(:model_name)
+          klass = object.model_name
+        elsif object.class.respond_to?(:model_name)
+          klass = object.class.model_name
+        elsif object.is_a?(Class)
+          klass = object
+        else
+          klass = object.class
+        end
 
-    def policy_name
-      "#{name}Policy"
-    end
+        "#{klass}Policy"
+      end
+
+      def scope_name
+        "#{policy_name}::Scope"
+      end
+
+      def policy_name
+        name = policy_evaluator
+        return name.name unless name.is_a?(String)
+        name
+      end
   end
 end

spec/pundit_spec.rb

@@ -41,6 +41,18 @@ class ArtificialBlog < Blog
     BlogPolicy
   end
 end
+class ArticleTag
+  def self.policy_class
+    Struct.new(:user, :tag) do
+      def show?
+        true
+      end
+      def destroy?
+        false
+      end
+    end
+  end
+end
 
 describe Pundit do
   let(:user) { stub }
@@ -49,6 +61,7 @@ describe Pundit do
   let(:article) { Article.new }
   let(:controller) { stub(:current_user => user, :params => { :action => "update" }).tap { |c| c.extend(Pundit) } }
   let(:artificial_blog) { ArtificialBlog.new }
+  let(:article_tag) { ArticleTag.new }
 
   describe ".policy_scope" do
     it "returns an instantiated policy scope given a plain model class" do
@@ -76,6 +89,10 @@ describe Pundit do
     it "throws an exception if the given policy scope can't be found" do
       expect { Pundit.policy_scope!(user, Article) }.to raise_error(Pundit::NotDefinedError)
     end
+
+    it "throws an exception if the given policy scope can't be found" do
+      expect { Pundit.policy_scope!(user, ArticleTag) }.to raise_error(Pundit::NotDefinedError)
+    end
   end
 
   describe ".policy" do
@@ -85,18 +102,6 @@ describe Pundit do
       policy.post.should == post
     end
 
-    it "returns an instantiated policy given a plain model instance with policy_class class method set" do
-      policy = Pundit.policy(user, artificial_blog)
-      policy.user.should == user
-      policy.blog.should == artificial_blog
-    end
-
-    it "returns an instantiated policy given a plain model class with policy_class class method set" do
-      policy = Pundit.policy(user, ArtificialBlog)
-      policy.user.should == user
-      policy.blog.should == ArtificialBlog
-    end
-
     it "returns an instantiated policy given an active model instance" do
       policy = Pundit.policy(user, comment)
       policy.user.should == user
@@ -119,6 +124,32 @@ describe Pundit do
       Pundit.policy(user, article).should be_nil
       Pundit.policy(user, Article).should be_nil
     end
+
+    describe "with .policy_class set on the model" do
+      it "returns an instantiated policy given a plain model instance" do
+        policy = Pundit.policy(user, artificial_blog)
+        policy.user.should == user
+        policy.blog.should == artificial_blog
+      end
+
+      it "returns an instantiated policy given a plain model class" do
+        policy = Pundit.policy(user, ArtificialBlog)
+        policy.user.should == user
+        policy.blog.should == ArtificialBlog
+      end
+
+      it "returns an instantiated policy given a plain model instance providing an anonymous class" do
+        policy = Pundit.policy(user, article_tag)
+        policy.user.should == user
+        policy.tag.should == article_tag
+      end
+
+      it "returns an instantiated policy given a plain model class providing an anonymous class" do
+        policy = Pundit.policy(user, ArticleTag)
+        policy.user.should == user
+        policy.tag.should == ArticleTag
+      end
+    end
   end
 
   describe ".policy!" do
@@ -173,6 +204,11 @@ describe Pundit do
       expect { controller.authorize(post, :destroy?) }.to raise_error(Pundit::NotAuthorizedError)
     end
 
+    it "works with anonymous class policies" do
+      controller.authorize(article_tag, :show?).should be_true
+      expect { controller.authorize(article_tag, :destroy?) }.to raise_error(Pundit::NotAuthorizedError)
+    end
+
     it "raises an error when the permission check fails" do
       expect { controller.authorize(Post.new) }.to raise_error(Pundit::NotAuthorizedError)
     end