Precompile config.filter_parameters in place

Applications may try to modify `config.filter_parameters` after
`Rails::Application#env_config` has already been memoized.  For example,
in the `development` environment, models with encrypted attributes will
append filters when the model is (re)loaded.  Prior to this commit, if
`config.precompile_filter_parameters` was enabled, such changes would
not be reflected in `env_config["action_dispatch.parameter_filter"]`.

This commit ensures that `env_config["action_dispatch.parameter_filter"]`
is the `config.filter_parameters` array itself, regardless of whether
`config.precompile_filter_parameters` is enabled.

Author: jonathanhefner

railties/lib/rails/application.rb

@@ -675,10 +675,11 @@ def coerce_same_site_protection(protection)
 
       def filter_parameters
         if config.precompile_filter_parameters
-          ActiveSupport::ParameterFilter.precompile_filters(config.filter_parameters)
-        else
-          config.filter_parameters
+          config.filter_parameters.replace(
+            ActiveSupport::ParameterFilter.precompile_filters(config.filter_parameters)
+          )
         end
+        config.filter_parameters
       end
   end
 end

railties/test/application/configuration_test.rb

@@ -557,6 +557,21 @@ class Comment < ActiveRecord::Base
       assert_equal filters, Rails.application.env_config["action_dispatch.parameter_filter"]
     end
 
+    test "filter_parameters reflects changes to config.filter_parameters after being precompiled" do
+      add_to_config <<~RUBY
+        config.filter_parameters += [/foo/, :bar]
+        config.precompile_filter_parameters = true
+      RUBY
+
+      app "development"
+
+      assert_not_empty Rails.application.env_config["action_dispatch.parameter_filter"]
+
+      Rails.application.config.filter_parameters << "baz.qux"
+
+      assert_includes Rails.application.env_config["action_dispatch.parameter_filter"], "baz.qux"
+    end
+
     test "config.precompile_filter_parameters is true by default for new apps" do
       app "development"