Preserve the serializer type when fragment caching

We were not previously cloning the type setting into the dynamically
generated cached/non-cached serializers for a given fragment-cached
serializer. This led to the type generated for JsonApi having the wrong
value when fragment caching is enabled by adding either :except or :only
options to cache.

This pulls the type setting from the fragment-cached serializer forward
onto the dynamic caching classes so it is preserved in the output.

lib/active_model/serializer/adapter/fragment_cache.rb

@@ -94,6 +94,10 @@ module ActiveModel
 
           cached.constantize.cache(klass._cache_options)
 
+          # Preserve the type setting in the cached/non-cached serializer classes
+          cached.constantize.type(klass._type)
+          non_cached.constantize.type(klass._type)
+
           cached.constantize.fragmented(serializer)
           non_cached.constantize.fragmented(serializer)
 

test/adapter/fragment_cache_test.rb

@@ -3,6 +3,14 @@ module ActiveModel
   class Serializer
     module Adapter
       class FragmentCacheTest < ActiveSupport::TestCase
+        TypedRoleSerializer = Class.new(ActiveModel::Serializer) do
+          type 'my-roles'
+          cache only: [:name], skip_digest: true
+          attributes :id, :name, :description
+
+          belongs_to :author
+        end
+
         def setup
           super
           @spam            = Spam::UnrelatedLink.new(id: 'spam-id-1')
@@ -31,8 +39,12 @@ module ActiveModel
           }
           assert_equal(@spam_hash.fetch, expected_result)
         end
-      end
-    end
-  end
-end
 
+        def test_fragment_fetch_with_type_override
+          serialization = serializable(Role.new(name: 'Another Author'), serializer: TypedRoleSerializer, adapter: :json_api).serializable_hash
+          assert_equal(TypedRoleSerializer._type, serialization.fetch(:data).fetch(:type))
+        end
+      end
+    end
+  end
+end