4 files changed, 32 insertions, 6 deletions
diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 064c9008e0..0265ab0c11 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,14 @@
+*   `scoping` no longer pollutes the current scope of sibling classes when using
+    STI. e.x.
+
+    StiOne.none.scoping do
+      StiTwo.all
+    end
+
+    Fixes #18806.
+
+    *Sean Griffin*
+
 *   `remove_reference` with `foreign_key: true` removes the foreign key before
     removing the column. This fixes a bug where it was not possible to remove
     the column on MySQL.
diff --git a/activerecord/lib/active_record/scoping.rb b/activerecord/lib/active_record/scoping.rb
index 3e43591672..fca4f1c9d3 100644
--- a/activerecord/lib/active_record/scoping.rb
+++ b/activerecord/lib/active_record/scoping.rb
@@ -11,11 +11,11 @@ module ActiveRecord
 
     module ClassMethods
       def current_scope #:nodoc:
-        ScopeRegistry.value_for(:current_scope, base_class.to_s)
+        ScopeRegistry.value_for(:current_scope, self.to_s)
       end
 
       def current_scope=(scope) #:nodoc:
-        ScopeRegistry.set_value_for(:current_scope, base_class.to_s, scope)
+        ScopeRegistry.set_value_for(:current_scope, self.to_s, scope)
       end
     end
 
diff --git a/activerecord/lib/active_record/scoping/named.rb b/activerecord/lib/active_record/scoping/named.rb
index a083deafe1..43c7b1c574 100644
--- a/activerecord/lib/active_record/scoping/named.rb
+++ b/activerecord/lib/active_record/scoping/named.rb
@@ -157,11 +157,20 @@ module ActiveRecord
 
           extension = Module.new(&block) if block
 
-          singleton_class.send(:define_method, name) do |*args|
-            scope = all.scoping { body.call(*args) }
-            scope = scope.extending(extension) if extension
+          if body.respond_to?(:to_proc)
+            singleton_class.send(:define_method, name) do |*args|
+              scope = all.scoping { instance_exec(*args, &body) }
+              scope = scope.extending(extension) if extension
 
-            scope || all
+              scope || all
+            end
+          else
+            singleton_class.send(:define_method, name) do |*args|
+              scope = all.scoping { body.call(*args) }
+              scope = scope.extending(extension) if extension
+
+              scope || all
+            end
           end
         end
       end
diff --git a/activerecord/test/cases/scoping/relation_scoping_test.rb b/activerecord/test/cases/scoping/relation_scoping_test.rb
index 02b32abebf..4bfffbe9c6 100644
--- a/activerecord/test/cases/scoping/relation_scoping_test.rb
+++ b/activerecord/test/cases/scoping/relation_scoping_test.rb
@@ -208,6 +208,12 @@ class RelationScopingTest < ActiveRecord::TestCase
     assert_equal [], DeveloperFilteredOnJoins.all
     assert_not_equal [], Developer.all
   end
+
+  def test_current_scope_does_not_pollute_other_subclasses
+    Post.none.scoping do
+      assert StiPost.all.any?
+    end
+  end
 end
 
 class NestedRelationScopingTest < ActiveRecord::TestCase