Merge pull request #29557 from kamipo/extract_build_scope_and_predicate_builder

Extract `build_scope` and `predicate_builder` in `Reflection`

activerecord/lib/active_record/associations/association_scope.rb

@@ -142,7 +142,7 @@ module ActiveRecord
             # Exclude the scope of the association itself, because that
             # was already merged in the #scope method.
             reflection.constraints.each do |scope_chain_item|
-              item = eval_scope(reflection.klass, table, scope_chain_item, owner)
+              item = eval_scope(reflection, table, scope_chain_item, owner)
 
               if scope_chain_item == refl.scope
                 scope.merge! item.except(:where, :includes)
@@ -163,9 +163,8 @@ module ActiveRecord
           scope
         end
 
-        def eval_scope(klass, table, scope, owner)
-          predicate_builder = PredicateBuilder.new(TableMetadata.new(klass, table))
-          ActiveRecord::Relation.create(klass, table, predicate_builder).instance_exec(owner, &scope)
+        def eval_scope(reflection, table, scope, owner)
+          reflection.build_scope(table).instance_exec(owner, &scope)
         end
     end
   end

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

@@ -40,15 +40,7 @@ module ActiveRecord
 
             constraint = build_constraint(klass, table, key, foreign_table, foreign_key)
 
-            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)
-
-            scope_chain_items.concat [klass_scope].compact
-
-            rel = scope_chain_items.inject(scope_chain_items.shift) do |left, right|
-              left.merge right
-            end
+            rel = reflection.join_scope(table)
 
             if rel && !rel.arel.constraints.empty?
               binds += rel.bound_attributes

activerecord/lib/active_record/reflection.rb

@@ -185,10 +185,17 @@ module ActiveRecord
       end
       deprecate :scope_chain
 
+      def join_scope(table)
+        predicate_builder = predicate_builder(table)
+        scope_chain_items = join_scopes(table, predicate_builder)
+        klass_scope       = klass_join_scope(table, predicate_builder)
+
+        scope_chain_items.inject(klass_scope || scope_chain_items.shift, &:merge!)
+      end
+
       def join_scopes(table, predicate_builder) # :nodoc:
         if scope
-          [ActiveRecord::Relation.create(klass, table, predicate_builder)
-            .instance_exec(&scope)]
+          [build_scope(table, predicate_builder).instance_exec(&scope)]
         else
           []
         end
@@ -200,11 +207,7 @@ module ActiveRecord
             scope.joins_values = scope.left_outer_joins_values = [].freeze
           }
         else
-          relation = ActiveRecord::Relation.create(
-            klass,
-            table,
-            predicate_builder,
-          )
+          relation = build_scope(table, predicate_builder)
           klass.send(:build_default_scope, relation)
         end
       end
@@ -287,12 +290,19 @@ module ActiveRecord
         JoinKeys.new(join_pk(association_klass), join_fk)
       end
 
+      def build_scope(table, predicate_builder = predicate_builder(table))
+        Relation.create(klass, table, predicate_builder)
+      end
+
       protected
         def actual_source_reflection # FIXME: this is a horrible name
           self
         end
 
       private
+        def predicate_builder(table)
+          PredicateBuilder.new(TableMetadata.new(klass, table))
+        end
 
         def join_pk(_)
           foreign_key