ask reflection for klass join reflection

activerecord/lib/active_record/associations/join_dependency/join_association.rb

@@ -42,20 +42,8 @@ def join_constraints(foreign_table, foreign_klass, join_type, tables, chain)
 
             predicate_builder = PredicateBuilder.new(TableMetadata.new(klass, table))
             scope_chain_items = reflection.join_scopes(table, predicate_builder)
+            klass_scope       = reflection.klass_join_scope(table, predicate_builder)
 
-            klass_scope =
-              if klass.current_scope
-                klass.current_scope.clone.tap { |scope|
-                  scope.joins_values = []
-                }
-              else
-                relation = ActiveRecord::Relation.create(
-                  klass,
-                  table,
-                  predicate_builder,
-                )
-                klass.send(:build_default_scope, relation)
-              end
             scope_chain_items.concat [klass_scope].compact
 
             rel = scope_chain_items.inject(scope_chain_items.shift) do |left, right|

activerecord/lib/active_record/reflection.rb

@@ -196,6 +196,21 @@ def join_scopes(table, predicate_builder) # :nodoc:
         end
       end
 
+      def klass_join_scope(table, predicate_builder) # :nodoc:
+        if klass.current_scope
+          klass.current_scope.clone.tap { |scope|
+            scope.joins_values = []
+          }
+        else
+          relation = ActiveRecord::Relation.create(
+            klass,
+            table,
+            predicate_builder,
+          )
+          klass.send(:build_default_scope, relation)
+        end
+      end
+
       def constraints
         chain.map(&:scopes).flatten
       end