`current_scope` shouldn't pollute sibling STI classes

It looks like the only reason `current_scope` was thread local on
`base_class` instead of `self` is to ensure that when we call a named
scope created with a proc on the parent class, it correctly uses the
default scope of the subclass. The reason this wasn't happening was
because the proc captured `self` as the parent class, and we're not
actually defining a real method. Using `instance_exec` fixes the
problem.

Fixes #18806

1 files changed, 6 insertions, 0 deletions

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