Fix merge conflicts from #19501

I'm making this commit separately because this has failing tests and
style nitpicks that I'd like to make as individual commits, to make the
changes I'm making explicit.

We still want a single merge commit at the end, however.

4 files changed, 28 insertions, 23 deletions

diff --git a/activerecord/lib/active_record/inheritance.rb b/activerecord/lib/active_record/inheritance.rb
index c26842014d..53a9a9b797 100644
--- a/activerecord/lib/active_record/inheritance.rb
+++ b/activerecord/lib/active_record/inheritance.rb
@@ -55,7 +55,7 @@ module ActiveRecord
           subclass = subclass_from_attributes(attrs)
         end
 
-        if subclass
+        if subclass && subclass != self
           subclass.new(*args, &block)
         else
           super
@@ -167,17 +167,23 @@ module ActiveRecord
       end
 
       def find_sti_class(type_name)
-        if store_full_sti_class
-          ActiveSupport::Dependencies.constantize(type_name)
-        else
-          compute_type(type_name)
+        subclass = begin
+          if store_full_sti_class
+            ActiveSupport::Dependencies.constantize(type_name)
+          else
+            compute_type(type_name)
+          end
+        rescue NameError
+          raise SubclassNotFound,
+            "The single-table inheritance mechanism failed to locate the subclass: '#{type_name}'. " +
+            "This error is raised because the column '#{inheritance_column}' is reserved for storing the class in case of inheritance. " +
+            "Please rename this column if you didn't intend it to be used for storing the inheritance class " +
+            "or overwrite #{name}.inheritance_column to use another column for that information."
+        end
+        unless subclass == self || descendants.include?(subclass)
+          raise SubclassNotFound, "Invalid single-table inheritance type: #{type_name} is not a subclass of #{name}"
         end
-      rescue NameError
-        raise SubclassNotFound,
-          "The single-table inheritance mechanism failed to locate the subclass: '#{type_name}'. " +
-          "This error is raised because the column '#{inheritance_column}' is reserved for storing the class in case of inheritance. " +
-          "Please rename this column if you didn't intend it to be used for storing the inheritance class " +
-          "or overwrite #{name}.inheritance_column to use another column for that information."
+        subclass
       end
 
       def type_condition(table = arel_table)
@@ -199,15 +205,7 @@ module ActiveRecord
         subclass_name = attrs.with_indifferent_access[inheritance_column]
 
         if subclass_name.present?
-          subclass = find_sti_class(subclass_name)
-
-          if subclass.name != self.name
-            unless descendants.include?(subclass)
-              raise ActiveRecord::SubclassNotFound.new("Invalid single-table inheritance type: #{subclass.name} is not a subclass of #{name}")
-            end
-
-            subclass
-          end
+          find_sti_class(subclass_name)
         end
       end
     end
diff --git a/activerecord/test/cases/associations/has_many_through_associations_test.rb b/activerecord/test/cases/associations/has_many_through_associations_test.rb
index cf730e4fe7..226ecf5447 100644
--- a/activerecord/test/cases/associations/has_many_through_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_through_associations_test.rb
@@ -1111,10 +1111,10 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_has_many_through_with_default_scope_on_the_target
     person = people(:michael)
-    assert_equal [posts(:thinking)], person.first_posts
+    assert_equal [posts(:thinking).id], person.first_posts.map(&:id)
 
     readers(:michael_authorless).update(first_post_id: 1)
-    assert_equal [posts(:thinking)], person.reload.first_posts
+    assert_equal [posts(:thinking).id], person.reload.first_posts.map(&:id)
   end
 
   def test_has_many_through_with_includes_in_through_association_scope
diff --git a/activerecord/test/cases/batches_test.rb b/activerecord/test/cases/batches_test.rb
index 9cb70ee239..da65336305 100644
--- a/activerecord/test/cases/batches_test.rb
+++ b/activerecord/test/cases/batches_test.rb
@@ -161,7 +161,7 @@ class EachTest < ActiveRecord::TestCase
     end
     # posts.first will be ordered using id only. Title order scope should not apply here
     assert_not_equal first_post, posts.first
-    assert_equal posts(:welcome), posts.first
+    assert_equal posts(:welcome).id, posts.first.id
   end
 
   def test_find_in_batches_should_not_ignore_the_default_scope_if_it_is_other_then_order
diff --git a/activerecord/test/models/post.rb b/activerecord/test/models/post.rb
index 81a18188d4..23cebe2602 100644
--- a/activerecord/test/models/post.rb
+++ b/activerecord/test/models/post.rb
@@ -185,6 +185,7 @@ class SubStiPost < StiPost
 end
 
 class FirstPost < ActiveRecord::Base
+  self.inheritance_column = :disabled
   self.table_name = 'posts'
   default_scope { where(:id => 1) }
 
@@ -193,6 +194,7 @@ class FirstPost < ActiveRecord::Base
 end
 
 class PostWithDefaultInclude < ActiveRecord::Base
+  self.inheritance_column = :disabled
   self.table_name = 'posts'
   default_scope { includes(:comments) }
   has_many :comments, :foreign_key => :post_id
@@ -204,6 +206,7 @@ class PostWithSpecialCategorization < Post
 end
 
 class PostWithDefaultScope < ActiveRecord::Base
+  self.inheritance_column = :disabled
   self.table_name = 'posts'
   default_scope { order(:title) }
 end
@@ -225,11 +228,13 @@ class PostWithIncludesDefaultScope < ActiveRecord::Base
 end
 
 class SpecialPostWithDefaultScope < ActiveRecord::Base
+  self.inheritance_column = :disabled
   self.table_name = 'posts'
   default_scope { where(:id => [1, 5,6]) }
 end
 
 class PostThatLoadsCommentsInAnAfterSaveHook < ActiveRecord::Base
+  self.inheritance_column = :disabled
   self.table_name = 'posts'
   has_many :comments, class_name: "CommentThatAutomaticallyAltersPostBody", foreign_key: :post_id
 
@@ -239,6 +244,7 @@ class PostThatLoadsCommentsInAnAfterSaveHook < ActiveRecord::Base
 end
 
 class PostWithAfterCreateCallback < ActiveRecord::Base
+  self.inheritance_column = :disabled
   self.table_name = 'posts'
   has_many :comments, foreign_key: :post_id
 
@@ -248,6 +254,7 @@ class PostWithAfterCreateCallback < ActiveRecord::Base
 end
 
 class PostWithCommentWithDefaultScopeReferencesAssociation < ActiveRecord::Base
+  self.inheritance_column = :disabled
   self.table_name = 'posts'
   has_many :comment_with_default_scope_references_associations, foreign_key: :post_id
   has_one :first_comment, class_name: "CommentWithDefaultScopeReferencesAssociation", foreign_key: :post_id