Trust `Object#dup` in `ActionController::Parameters`, using `#initialize_copy` to manually duplicate the underlying parameters hash

It looks like `ActionController::Parameters#dup` is leftover from when the class inherited from `Hash`. We can just trust `#dup`, which already copies the `@permitted` instance variable (confirmed by tests). We still define a `#initialize_copy` to make `@parameters` a copy that can be mutated without affecting the original instance.

1 files changed, 19 insertions, 1 deletions

diff --git a/actionpack/test/controller/parameters/dup_test.rb b/actionpack/test/controller/parameters/dup_test.rb
index cf273933bd..ac5a9d94d0 100644
--- a/actionpack/test/controller/parameters/dup_test.rb
+++ b/actionpack/test/controller/parameters/dup_test.rb
@@ -17,9 +17,27 @@ class ParametersDupTest < ActiveSupport::TestCase
     )
   end
 
-  test "changes on a duplicate do not affect the original" do
+  test "a duplicate maintains the original's permitted status" do
+    @params.permit!
+    dupped_params = @params.dup
+    assert dupped_params.permitted?
+  end
+
+  test "a duplicate maintains the original's parameters" do
+    @params.permit!
+    dupped_params = @params.dup
+    assert_equal @params.to_h, dupped_params.to_h
+  end
+
+  test "changes to a duplicate's parameters do not affect the original" do
     dupped_params = @params.dup
     dupped_params.delete(:person)
     assert_not_equal @params, dupped_params
   end
+
+  test "changes tp a duplicate's permitted status do not affect the original" do
+    dupped_params = @params.dup
+    dupped_params.permit!
+    assert_not_equal @params, dupped_params
+  end
 end