Fix ApplicationController.renderer.defaults.merge!

Previously, users were trying to modify a frozen Hash. Includes a
regression test :)

Fixes #22975

2 files changed, 9 insertions, 1 deletions

diff --git a/actionpack/lib/action_controller/renderer.rb b/actionpack/lib/action_controller/renderer.rb
index e4d19e9dba..2775a24e56 100644
--- a/actionpack/lib/action_controller/renderer.rb
+++ b/actionpack/lib/action_controller/renderer.rb
@@ -45,7 +45,7 @@ module ActionController
     }.freeze
 
     # Create a new renderer instance for a specific controller class.
-    def self.for(controller, env = {}, defaults = DEFAULTS)
+    def self.for(controller, env = {}, defaults = DEFAULTS.dup)
       new(controller, env, defaults)
     end
 
diff --git a/actionpack/test/controller/renderer_test.rb b/actionpack/test/controller/renderer_test.rb
index 16d24fa82a..372c09bc23 100644
--- a/actionpack/test/controller/renderer_test.rb
+++ b/actionpack/test/controller/renderer_test.rb
@@ -87,6 +87,14 @@ class RendererTest < ActiveSupport::TestCase
     assert_equal "<p>1\n<br />2</p>", render[inline: '<%= simple_format "1\n2" %>']
   end
 
+  test 'rendering with user specified defaults' do
+    ApplicationController.renderer.defaults.merge!({ hello: 'hello', https: true })
+    renderer = ApplicationController.renderer.new
+    content = renderer.render inline: '<%= request.ssl? %>'
+
+    assert_equal 'true', content
+  end
+
   private
     def render
       @render ||= ApplicationController.renderer.method(:render)