Allow sideload to be referenced multiple times

If the same resource was sideloaded twice, the next level of sideloading
would only apply once. This fixes that logic to allow this up to five
times (without cutoff there is infinite recursion).

Fixes #41

Author: Lee Richmond

lib/jsonapi_compliable/sideload.rb

@@ -310,7 +310,10 @@ def sideload(name)
     # @return [Hash] The nested include hash
     # @api private
     def to_hash(processed = [])
-      return { name => {} } if processed.include?(self)
+      # Cut off at 5 recursions
+      if processed.select { |p| p == self }.length == 5
+        return { name => {} }
+      end
       processed << self
 
       result = { name => {} }.tap do |hash|

spec/integration/rails/finders_spec.rb

@@ -295,6 +295,35 @@ def json
       end
     end
 
+    context 'sideloading the same "type", then adding another sideload' do
+      before do
+        Author.class_eval do
+          has_many :other_books, class_name: 'Book'
+        end
+
+        SerializableAuthor.class_eval do
+          has_many :other_books
+        end
+
+        Integration::AuthorResource.class_eval do
+          has_many :other_books,
+            scope: -> { Book.all },
+            foreign_key: :author_id,
+            resource: Integration::BookResource
+        end
+      end
+
+      it 'works' do
+        book2.genre = Genre.create! name: 'Comedy'
+        book2.save!
+        get :index, params: {
+          filter: { books: { id: book1.id }, other_books: { id: book2.id } },
+          include: 'books.genre,other_books.genre'
+        }
+        expect(json_includes('genres').length).to eq(2)
+      end
+    end
+
     context 'sideloading polymorphic belongs_to' do
       it 'allows extra fields for the sideloaded resource' do
         get :index, params: {