`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

2 files changed, 15 insertions, 6 deletions

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