Add config.serializer_lookup_enabled that defaults true

CHANGELOG.md

@@ -21,8 +21,10 @@ Features:
 - [#1127](https://github.com/rails-api/active_model_serializers/pull/1127) Add support for nested
     associations for JSON and Attributes adapters via the `include` option (@NullVoxPopuli, @beauby).
 - [#1050](https://github.com/rails-api/active_model_serializers/pull/1050) Add support for toplevel jsonapi member (@beauby, @bf4)
-- [#tbd](https://github.com/rails-api/active_model_serializers/pull/tbd) Rename ArraySerializer to
+- [#1251](https://github.com/rails-api/active_model_serializers/pull/1251) Rename ArraySerializer to
     CollectionSerializer for clarity, add ActiveModelSerializers.config.collection_serializer (@bf4)
+- [#1295](https://github.com/rails-api/active_model_serializers/pull/1295) Add config `serializer_lookup_enabled` that,
+  when disabled, requires serializers to explicitly specified. (@trek)
 
 Fixes:
 - [#1239](https://github.com/rails-api/active_model_serializers/pull/1239) Fix duplicates in JSON API compound documents (@beauby)

docs/general/configuration_options.md

@@ -5,7 +5,7 @@ The following configuration options can be set on `ActiveModel::Serializer.confi
 ## General
 
 - `adapter`: The [adapter](adapters.md) to use. Possible values: `:attributes, :json, :json_api`. Default: `:attributes`.
-- `automatic_lookup`: Whether serializer should be automatically looked up or manually provided. Default: `true`
+- `serializer_lookup_enabled`: When `false`, serializers must be explicitly specified. Default: `true`
 
 ## JSON API
 

lib/action_controller/serialization.rb

@@ -27,10 +27,6 @@ module ActionController
     end
 
     def get_serializer(resource, options = {})
-      unless options[:serializer] || options[:each_serializer] || ActiveModel::Serializer.config.automatic_lookup
-        return resource
-      end
-
       if !use_adapter?
         warn 'ActionController::Serialization#use_adapter? has been removed. '\
           "Please pass 'adapter: false' or see ActiveSupport::SerializableResource.new"

lib/active_model/serializer.rb

@@ -208,6 +208,7 @@ module ActiveModel
     #   2. try again with superclass, if present
     #   3. nil
     def self.get_serializer_for(klass)
+      return nil unless config.serializer_lookup_enabled
       serializers_cache.fetch_or_store(klass) do
         # NOTE(beauby): When we drop 1.9.3 support we can lazify the map for perfs.
         serializer_class = serializer_lookup_chain_for(klass).map(&:safe_constantize).find { |x| x && x < ActiveModel::Serializer }

lib/active_model/serializer/configuration.rb

@@ -9,6 +9,7 @@ module ActiveModel
       included do |base|
         config = base.config
         config.collection_serializer = ActiveModel::Serializer::CollectionSerializer
+        config.serializer_lookup_enabled = true
 
         def config.array_serializer=(collection_serializer)
           self.collection_serializer = collection_serializer
@@ -20,7 +21,6 @@ module ActiveModel
 
         config.adapter = :attributes
         config.jsonapi_resource_type = :plural
-        config.automatic_lookup = true
       end
     end
   end

test/serializers/serializer_for_test.rb

@@ -57,7 +57,7 @@ module ActiveModel
 
         def test_serializer_for_non_ams_serializer
           serializer = ActiveModel::Serializer.serializer_for(@tweet)
-          assert_nil(serializer)
+          assert_equal nil, serializer
         end
 
         def test_serializer_for_existing_serializer
@@ -65,6 +65,13 @@ module ActiveModel
           assert_equal ProfileSerializer, serializer
         end
 
+        def test_serializer_for_existing_serializer_with_lookup_disabled
+          serializer = with_serializer_lookup_disabled do
+            ActiveModel::Serializer.serializer_for(@profile)
+          end
+          assert_equal nil, serializer
+        end
+
         def test_serializer_for_not_existing_serializer
           serializer = ActiveModel::Serializer.serializer_for(@model)
           assert_equal nil, serializer
@@ -75,21 +82,51 @@ module ActiveModel
           assert_equal ProfileSerializer, serializer
         end
 
+        def test_serializer_inherited_serializer_with_lookup_disabled
+          serializer = with_serializer_lookup_disabled do
+            ActiveModel::Serializer.serializer_for(@my_profile)
+          end
+          assert_equal nil, serializer
+        end
+
         def test_serializer_custom_serializer
           serializer = ActiveModel::Serializer.serializer_for(@custom_profile)
           assert_equal ProfileSerializer, serializer
         end
 
+        def test_serializer_custom_serializer_with_lookup_disabled
+          serializer = with_serializer_lookup_disabled do
+            ActiveModel::Serializer.serializer_for(@custom_profile)
+          end
+          assert_equal ProfileSerializer, serializer
+        end
+
         def test_serializer_for_namespaced_resource
           post = ResourceNamespace::Post.new
           serializer = ActiveModel::Serializer.serializer_for(post)
-          assert_equal(ResourceNamespace::PostSerializer, serializer)
+          assert_equal ResourceNamespace::PostSerializer, serializer
+        end
+
+        def test_serializer_for_namespaced_resource_with_lookup_disabled
+          post = ResourceNamespace::Post.new
+          serializer = with_serializer_lookup_disabled do
+            ActiveModel::Serializer.serializer_for(post)
+          end
+          assert_equal nil, serializer
         end
 
         def test_serializer_for_nested_resource
           comment = ResourceNamespace::Comment.new
           serializer = ResourceNamespace::PostSerializer.serializer_for(comment)
-          assert_equal(ResourceNamespace::PostSerializer::CommentSerializer, serializer)
+          assert_equal ResourceNamespace::PostSerializer::CommentSerializer, serializer
+        end
+
+        def test_serializer_for_nested_resource_with_lookup_disabled
+          comment = ResourceNamespace::Comment.new
+          serializer = with_serializer_lookup_disabled do
+            ResourceNamespace::PostSerializer.serializer_for(comment)
+          end
+          assert_equal nil, serializer
         end
       end
     end

test/support/serialization_testing.rb

@@ -31,6 +31,14 @@ module SerializationTesting
     ActiveModel::Serializer.config.replace(old_config)
   end
 
+  def with_serializer_lookup_disabled
+    original_serializer_lookup = ActiveModelSerializers.config.serializer_lookup_enabled
+    ActiveModelSerializers.config.serializer_lookup_enabled = false
+    yield
+  ensure
+    ActiveModelSerializers.config.serializer_lookup_enabled = original_serializer_lookup
+  end
+
   def serializable(resource, options = {})
     ActiveModel::SerializableResource.new(resource, options)
   end