Only flash if the request object that is loaded supports it (#4950)

lib/devise/controllers/helpers.rb

@@ -268,7 +268,7 @@ module Devise
       # Check if flash messages should be emitted. Default is to do it on
       # navigational formats
       def is_flashing_format?
-        is_navigational_format?
+        request.respond_to?(:flash) && is_navigational_format?
       end
 
       private

lib/devise/failure_app.rb

@@ -242,7 +242,7 @@ module Devise
     # Check if flash messages should be emitted. Default is to do it on
     # navigational formats
     def is_flashing_format?
-      is_navigational_format?
+      request.respond_to?(:flash) && is_navigational_format?
     end
 
     def request_format

test/controllers/helpers_test.rb

@@ -312,6 +312,16 @@ class ControllerAuthenticatableTest < Devise::ControllerTestCase
     end
   end
 
+  test 'is_flashing_format? depends on is_navigation_format?' do
+    @controller.expects(:is_navigational_format?).returns(true)
+    assert @controller.is_flashing_format?
+  end
+
+  test 'is_flashing_format? is guarded against flash (middleware) not being loaded' do
+    @controller.request.expects(:respond_to?).with(:flash).returns(false)
+    refute @controller.is_flashing_format?
+  end
+
   test 'is not a devise controller' do
     refute @controller.devise_controller?
   end

test/failure_app_test.rb

@@ -44,6 +44,10 @@ class FailureTest < ActiveSupport::TestCase
     end
   end
 
+  class RequestWithoutFlashSupport < ActionDispatch::Request
+    undef_method :flash
+  end
+
   def self.context(name, &block)
     instance_eval(&block)
   end
@@ -66,7 +70,7 @@ class FailureTest < ActiveSupport::TestCase
     end
 
     @response = (env.delete(:app) || Devise::FailureApp).call(env).to_a
-    @request  = ActionDispatch::Request.new(env)
+    @request  = (env.delete(:request_klass) || ActionDispatch::Request).new(env)
   end
 
   context 'When redirecting' do
@@ -343,4 +347,11 @@ class FailureTest < ActiveSupport::TestCase
       assert_equal Devise::FailureApp.new.lazy_loading_works?, "yes it does"
     end
   end
+  context "Without Flash Support" do
+    test "returns to the default redirect location without a flash message" do
+      call_failure request_klass: RequestWithoutFlashSupport
+      assert_equal 302, @response.first
+      assert_equal 'http://test.host/users/sign_in', @response.second['Location']
+    end
+  end
 end