add raise_cannot_infer_root_key_error to config

lib/active_model/serializer.rb

@@ -146,6 +146,8 @@ module ActiveModel
     config.jsonapi_include_toplevel_object = false
     config.jsonapi_use_foreign_key_on_belongs_to_relationship = false
     config.include_data_default = true
+    # Raise ActiveModel::Serializer::CollectionSerializer::CannotInferRootKeyError when cannot infer root key from collection type
+    config.raise_cannot_infer_root_key_error = true
 
     # For configuring how serializers are found.
     # This should be an array of procs.

lib/active_model/serializer/collection_serializer.rb

@@ -48,8 +48,11 @@ module ActiveModel
         key ||= object.respond_to?(:name) ? object.name && object.name.underscore : nil
         # 4. key may be nil for empty collection and no serializer option
         key &&= key.pluralize
-        # 5. fail if the key cannot be determined
-        key || fail(ArgumentError, 'Cannot infer root key from collection type. Please specify the root or each_serializer option, or render a JSON String')
+        if raise_cannot_infer_root_key_error?
+          # 5. fail if the key cannot be determined
+          key || fail(CannotInferRootKeyError, 'Cannot infer root key from collection type. Please specify the root or each_serializer option, or render a JSON String')
+        end
+        key
       end
       # rubocop:enable Metrics/CyclomaticComplexity
 
@@ -60,12 +63,18 @@ module ActiveModel
           object.respond_to?(:size)
       end
 
+      class CannotInferRootKeyError < StandardError; end
+
       protected
 
       attr_reader :serializers, :options
 
       private
 
+      def raise_cannot_infer_root_key_error?
+        ActiveModelSerializers.config.raise_cannot_infer_root_key_error
+      end
+
       def serializers_from_resources
         serializer_context_class = options.fetch(:serializer_context_class, ActiveModel::Serializer)
         object.map do |resource|

test/collection_serializer_test.rb

@@ -22,6 +22,8 @@ module ActiveModel
         type 'messages'
       end
 
+      class NonTypeSerializer < ActiveModel::Serializer; end
+
       def setup
         @singular_model = SingularModel.new
         @has_many_model = HasManyModel.new
@@ -95,18 +97,36 @@ module ActiveModel
         resource = []
         resource.define_singleton_method(:name) { nil }
         serializer = collection_serializer.new(resource)
-        assert_raise ArgumentError do
+        assert_raise ActiveModel::Serializer::CollectionSerializer::CannotInferRootKeyError do
           serializer.json_key
         end
       end
 
       def test_json_key_with_resource_without_name_and_no_serializers
         serializer = collection_serializer.new([])
-        assert_raise ArgumentError do
+        assert_raise ActiveModel::Serializer::CollectionSerializer::CannotInferRootKeyError do
           serializer.json_key
         end
       end
 
+      def test_json_key_with_empty_resources_with_non_type_serializer
+        resource = []
+        serializer = collection_serializer.new(resource, serializer: NonTypeSerializer)
+        assert_raise ActiveModel::Serializer::CollectionSerializer::CannotInferRootKeyError do
+          serializer.json_key
+        end
+      end
+
+      def test_json_key_with_empty_resources_with_non_type_serializer_when_raise_cannot_infer_root_key_error_is_false
+        previous_raise_cannot_infer_root_key_error = ActiveModelSerializers.config.raise_cannot_infer_root_key_error
+        ActiveModelSerializers.config.raise_cannot_infer_root_key_error = false
+        resource = []
+        serializer = collection_serializer.new(resource, serializer: NonTypeSerializer)
+        assert_nil serializer.json_key
+      ensure
+        ActiveModelSerializers.config.raise_cannot_infer_root_key_error = previous_raise_cannot_infer_root_key_error
+      end
+
       def test_json_key_with_empty_resources_with_serializer
         resource = []
         serializer = collection_serializer.new(resource, serializer: MessagesSerializer)