Merge pull request rails#41901 from Shopify/cache-base-class

Precompute Inheritance.base_class

Author: byroot

activerecord/lib/active_record/inheritance.rb

@@ -43,6 +43,8 @@ module Inheritance
       # Determines whether to store the full constant name including namespace when using STI.
       # This is true, by default.
       class_attribute :store_full_sti_class, instance_writer: false, default: true
+
+      set_base_class
     end
 
     module ClassMethods
@@ -98,17 +100,7 @@ def finder_needs_type_condition? #:nodoc:
       #
       # If B < A and C < B and if A is an abstract_class then both B.base_class
       # and C.base_class would return B as the answer since A is an abstract_class.
-      def base_class
-        unless self < Base
-          raise ActiveRecordError, "#{name} doesn't belong in a hierarchy descending from ActiveRecord"
-        end
-
-        if superclass == Base || superclass.abstract_class?
-          self
-        else
-          superclass.base_class
-        end
-      end
+      attr_reader :base_class
 
       # Returns whether the class is a base class.
       # See #base_class for more information.
@@ -218,10 +210,24 @@ def polymorphic_class_for(name)
       end
 
       def inherited(subclass)
+        subclass.set_base_class
         subclass.instance_variable_set(:@_type_candidates_cache, Concurrent::Map.new)
         super
       end
 
+      def dup # :nodoc:
+        # `initialize_dup` / `initialize_copy` don't work when defined
+        # in the `singleton_class`.
+        other = super
+        other.set_base_class
+        other
+      end
+
+      def initialize_clone(other) # :nodoc:
+        super
+        set_base_class
+      end
+
       protected
         # Returns the class type of the record using the current module as a prefix. So descendants of
         # MyApp::Business::Account would appear as MyApp::Business::AccountSubclass.
@@ -253,6 +259,24 @@ def compute_type(type_name)
           end
         end
 
+        def set_base_class # :nodoc:
+          @base_class = begin
+            if self == Base
+              self
+            else
+              unless self < Base
+                raise ActiveRecordError, "#{name} doesn't belong in a hierarchy descending from ActiveRecord"
+              end
+
+              if superclass == Base || superclass.abstract_class?
+                self
+              else
+                superclass.base_class
+              end
+            end
+          end
+        end
+
       private
         # Called by +instantiate+ to decide which class to use for a new
         # record instance. For single-table inheritance, we check the record

activerecord/test/cases/inheritance_test.rb

@@ -190,8 +190,9 @@ def test_abstract_inheritance_base_class
   end
 
   def test_base_class_activerecord_error
-    klass = Class.new { include ActiveRecord::Inheritance }
-    assert_raise(ActiveRecord::ActiveRecordError) { klass.base_class }
+    assert_raise(ActiveRecord::ActiveRecordError) do
+      Class.new { include ActiveRecord::Inheritance }
+    end
   end
 
   def test_a_bad_type_column