Move argument validation into match

activerecord/lib/active_record/dynamic_finder_match.rb

@@ -36,6 +36,10 @@ module ActiveRecord
     def bang?
       false
     end
+
+    def valid_arguments?(arguments)
+      arguments.size >= @attribute_names.size
+    end
   end
 
   class FindBy < DynamicFinderMatch
@@ -65,5 +69,9 @@ module ActiveRecord
         new(:first, $2, $1 == 'initialize' ? :new : :create)
       end
     end
+
+    def valid_arguments?(arguments)
+      arguments.size == 1 && arguments.first.is_a?(Hash) || super
+    end
   end
 end

activerecord/lib/active_record/dynamic_matchers.rb

@@ -25,7 +25,7 @@ module ActiveRecord
       if match = (DynamicFinderMatch.match(method_id) || DynamicScopeMatch.match(method_id))
         attribute_names = match.attribute_names
         super unless all_attributes_exists?(attribute_names)
-        if !(match.is_a?(DynamicFinderMatch) && match.instantiator? && arguments.first.is_a?(Hash)) && arguments.size < attribute_names.size
+        unless match.valid_arguments?(arguments)
           method_trace = "#{__FILE__}:#{__LINE__}:in `#{method_id}'"
           backtrace = [method_trace] + caller
           raise ArgumentError, "wrong number of arguments (#{arguments.size} for #{attribute_names.size})", backtrace

activerecord/lib/active_record/dynamic_scope_match.rb

@@ -19,5 +19,9 @@ module ActiveRecord
 
     attr_reader :scope, :attribute_names
     alias :scope? :scope
+
+    def valid_arguments?(arguments)
+      arguments.size >= @attribute_names.size
+    end
   end
 end