Fix usage of self.inherited

This commit fixes issue #50003 where using `super` after adding
relations to the subclass or defining filter attributes in the subclass
in the method `self.inherited` lead to warnings and removed
previously defined filter_attributes

activerecord/lib/active_record/core.rb

@@ -384,8 +384,8 @@ def inherited(subclass)
             @arel_table = nil
             @predicate_builder = nil
             @inspection_filter = nil
-            @filter_attributes = nil
-            @generated_association_methods = nil
+            @filter_attributes ||= nil
+            @generated_association_methods ||= nil
           end
         end
 

activerecord/test/cases/inherited_test.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+
+module Inherited
+  # When running the test with `RAILS_STRICT_WARNINGS` enabled, the `belongs_to`
+  # call should not emit a warning that the constant `GeneratedAssociationMethods`
+  # is already defined.
+  class Person < ActiveRecord::Base; end
+
+  class Device < ActiveRecord::Base
+    def self.inherited(subclass)
+      subclass.belongs_to :person, inverse_of: subclass.name.demodulize.tableize.to_sym
+      subclass.filter_attributes = [:secret_attribute, :"#{subclass.name.demodulize.downcase}_key"]
+      super
+    end
+  end
+
+  class Computer < Device; end
+
+  class Vehicle < ActiveRecord::Base
+    def self.inherited(subclass)
+      super
+      subclass.belongs_to :person, inverse_of: subclass.name.demodulize.tableize.to_sym
+      subclass.filter_attributes = [:secret_attribute, :"#{subclass.name.demodulize.downcase}_key"]
+    end
+  end
+
+  class Car < Vehicle; end
+end
+
+class InheritedTest < ActiveRecord::TestCase
+  def test_super_before_filter_attributes
+    assert_equal %i[secret_attribute car_key], Inherited::Car.filter_attributes
+  end
+
+  def test_super_after_filter_attributes
+    assert_equal %i[secret_attribute computer_key], Inherited::Computer.filter_attributes
+  end
+end