add `ActionController::Parameters#merge!`

This method has the same behavior as `Hash#merge!`, returns current
`ActionController::Parameters`.

actionpack/CHANGELOG.md

+*   Add `ActionController::Parameters#merge!`, which behaves the same as `Hash#merge!`.
+
+    *Yuji Yaginuma*
+
 *   Allow keys not found in RACK_KEY_TRANSLATION for setting the environment when rendering
     arbitrary templates.
 

actionpack/lib/action_controller/metal/strong_parameters.rb

@@ -573,6 +573,13 @@ def merge(other_hash)
       )
     end
 
+    # Returns current <tt>ActionController::Parameters</tt> instance which
+    # +other_hash+ merges into current hash.
+    def merge!(other_hash)
+      @parameters.merge!(other_hash.to_h)
+      self
+    end
+
     # This is required by ActiveModel attribute assignment, so that user can
     # pass +Parameters+ to a mass assignment methods in a model. It should not
     # matter as we are using +HashWithIndifferentAccess+ internally.

actionpack/test/controller/parameters/parameters_permit_test.rb

@@ -244,6 +244,23 @@ def walk_permitted(params)
     assert merged_params[:id]
   end
 
+  test "not permitted is sticky beyond merge!" do
+    assert_not @params.merge!(a: "b").permitted?
+  end
+
+  test "permitted is sticky beyond merge!" do
+    @params.permit!
+    assert @params.merge!(a: "b").permitted?
+  end
+
+  test "merge! with parameters" do
+    other_params = ActionController::Parameters.new(id: "1234").permit!
+    @params.merge!(other_params)
+
+    assert_equal "1234", @params[:id]
+    assert_equal "32", @params[:person][:age]
+  end
+
   test "modifying the parameters" do
     @params[:person][:hometown] = "Chicago"
     @params[:person][:family] = { brother: "Jonas" }