Build string set when `filter_attributes` is assigned

It would allow `filter_attributes` to be reused across multiple
calls to `#inspect` or `#pretty_print`.

- Add `require "set"`
- Remove `filter_attributes` instance reader. I think there is no need
to keep it.

2 files changed, 19 insertions, 7 deletions

diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index d5d2c70a8a..0002941ff6 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -3,6 +3,7 @@
 require "active_support/core_ext/hash/indifferent_access"
 require "active_support/core_ext/string/filters"
 require "concurrent/map"
+require "set"
 
 module ActiveRecord
   module Core
@@ -125,9 +126,7 @@ module ActiveRecord
 
       class_attribute :default_connection_handler, instance_writer: false
 
-      ##
-      # Specifies columns which shouldn't be exposed while calling #inspect.
-      class_attribute :filter_attributes, instance_writer: false, default: []
+      self.filter_attributes = []
 
       def self.connection_handler
         ActiveRecord::RuntimeRegistry.connection_handler || default_connection_handler
@@ -227,6 +226,20 @@ module ActiveRecord
         end
       end
 
+      # Returns columns which shouldn't be exposed while calling #inspect.
+      def filter_attributes
+        if defined?(@filter_attributes)
+          @filter_attributes
+        else
+          superclass.filter_attributes
+        end
+      end
+
+      # Specifies columns which shouldn't be exposed while calling #inspect.
+      def filter_attributes=(attributes_names)
+        @filter_attributes = attributes_names.map(&:to_s).to_set
+      end
+
       # Returns a string like 'Post(id:integer, title:string, body:text)'
       def inspect
         if self == Base
@@ -582,9 +595,7 @@ module ActiveRecord
       end
 
       def filter_attribute?(attribute_name)
-        filter_attributes = self.filter_attributes.map(&:to_s).to_set
-
-        filter_attributes.include?(attribute_name) && !read_attribute(attribute_name).nil?
+        self.class.filter_attributes.include?(attribute_name) && !read_attribute(attribute_name).nil?
       end
   end
 end
diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index 83192edb39..44f6af5d4a 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -3,6 +3,7 @@
 require "isolation/abstract_unit"
 require "rack/test"
 require "env_helpers"
+require "set"
 
 class ::MyMailInterceptor
   def self.delivering_email(email); email; end
@@ -2049,7 +2050,7 @@ module ApplicationTests
       RUBY
       app "development"
       assert_equal [ :password, :credit_card_number ], Rails.application.config.filter_parameters
-      assert_equal [ :password, :credit_card_number ], ActiveRecord::Base.filter_attributes
+      assert_equal [ "password", "credit_card_number" ].to_set, ActiveRecord::Base.filter_attributes
     end
 
     private