Use symbol of mime type instead of object to get correct parser

After registering new `:json` mime type `parsers.fetch` can't find the mime type because new mime type is not equal to old one. Using symbol of the mime type as key on parsers hash solves the problem.

Closes rails#23766

Author: meinac

actionpack/lib/action_controller/test_case.rb

@@ -52,7 +52,7 @@ def initialize(env, session)
       self.session = session
       self.session_options = TestSession::DEFAULT_OPTIONS
       @custom_param_parsers = {
-        Mime[:xml] => lambda { |raw_post| Hash.from_xml(raw_post)['hash'] }
+        xml: lambda { |raw_post| Hash.from_xml(raw_post)['hash'] }
       }
     end
 
@@ -105,7 +105,7 @@ def assign_parameters(routes, controller_path, action, parameters, generated_pat
           when :url_encoded_form
             data = non_path_parameters.to_query
           else
-            @custom_param_parsers[content_mime_type] = ->(_) { non_path_parameters }
+            @custom_param_parsers[content_mime_type.symbol] = ->(_) { non_path_parameters }
             data = non_path_parameters.to_query
           end
         end

actionpack/lib/action_dispatch/http/parameters.rb

@@ -4,7 +4,7 @@ module Parameters
       PARAMETERS_KEY = 'action_dispatch.request.path_parameters'
 
       DEFAULT_PARSERS = {
-        Mime[:json] => lambda { |raw_post|
+        Mime[:json].symbol => -> (raw_post) {
           data = ActiveSupport::JSON.decode(raw_post)
           data.is_a?(Hash) ? data : {:_json => data}
         }
@@ -51,7 +51,7 @@ def path_parameters
       def parse_formatted_parameters(parsers)
         return yield if content_length.zero?
 
-        strategy = parsers.fetch(content_mime_type) { return yield }
+        strategy = parsers.fetch(content_mime_type.symbol) { return yield }
 
         begin
           strategy.call(raw_post)

actionpack/test/controller/webservice_test.rb

@@ -65,7 +65,7 @@ def test_put_json
 
   def test_register_and_use_json_simple
     with_test_route_set do
-      with_params_parsers Mime[:json] => Proc.new { |data| ActiveSupport::JSON.decode(data)['request'].with_indifferent_access } do
+      with_params_parsers json: Proc.new { |data| ActiveSupport::JSON.decode(data)['request'].with_indifferent_access } do
         post "/",
           params: '{"request":{"summary":"content...","title":"JSON"}}',
           headers: { 'CONTENT_TYPE' => 'application/json' }
@@ -99,7 +99,7 @@ def test_dasherized_keys_as_json
   def test_parsing_json_doesnot_rescue_exception
     req = Class.new(ActionDispatch::Request) do
       def params_parsers
-        { Mime[:json] => Proc.new { |data| raise Interrupt } }
+        { json: Proc.new { |data| raise Interrupt } }
       end
 
       def content_length; get_header('rack.input').length; end

actionpack/test/dispatch/request/json_params_parsing_test.rb

@@ -150,6 +150,22 @@ def teardown
     )
   end
 
+  test "parses json params after custom json mime type registered" do
+    Mime::Type.register "application/json", :json, %w(application/vnd.api+json)
+    assert_parses(
+      {"user" => {"username" => "meinac"}, "username" => "meinac"},
+      "{\"username\": \"meinac\"}", { 'CONTENT_TYPE' => 'application/json' }
+    )
+  end
+
+  test "parses json params after custom json mime type registered with synonym" do
+    Mime::Type.register "application/json", :json, %w(application/vnd.api+json)
+    assert_parses(
+      {"user" => {"username" => "meinac"}, "username" => "meinac"},
+      "{\"username\": \"meinac\"}", { 'CONTENT_TYPE' => 'application/vnd.api+json' }
+    )
+  end
+
   private
     def assert_parses(expected, actual, headers = {})
       with_test_routing(UsersController) do