require Strings, not Symbols

activesupport/lib/active_support/dependencies.rb

@@ -177,6 +177,7 @@ def require_or_load(file_name)
       end
 
       def require_dependency(file_name, message = "No such file to load -- %s")
+        raise ArgumentError, "the file name must be a String -- you passed #{file_name.inspect}"
         Dependencies.depend_on(file_name, false, message)
       end
 

railties/lib/rails/application/metal_loader.rb

@@ -34,7 +34,7 @@ def load_metals!(list)
           Dir.glob("#{path}/**/*.rb").sort.each do |metal_path|
             metal = metal_path.sub(matcher, '\1').to_sym
             next unless list.include?(metal) || list.include?(:all)
-            require_dependency metal
+            require_dependency metal.to_s
             metals << metal
           end
         end