`:through`, `:source`, and `:source_type` are valid for through association

activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb

@@ -75,7 +75,6 @@ def middle_reflection(join_model)
       def middle_options(join_model)
         middle_options = {}
         middle_options[:class_name] = "#{lhs_model.name}::#{join_model.name}"
-        middle_options[:source] = join_model.left_reflection.name
         if options.key? :foreign_key
           middle_options[:foreign_key] = options[:foreign_key]
         end

activerecord/lib/active_record/associations/builder/has_many.rb

@@ -7,7 +7,9 @@ def self.macro
     end
 
     def self.valid_options(options)
-      super + [:primary_key, :dependent, :as, :through, :source, :source_type, :inverse_of, :counter_cache, :join_table, :foreign_type, :index_errors]
+      valid = super + [:primary_key, :dependent, :as, :inverse_of, :counter_cache, :join_table, :foreign_type, :index_errors]
+      valid += [:through, :source, :source_type] if options[:through]
+      valid
     end
 
     def self.valid_dependent_options