Scala (as of 2.7.7) adds a public method $tag() to classes. It's not particularly pretty (and $tag() is apparently deprecated) but it's there. (See http://programming-scala.labs.oreilly.com/ch14.html#CommandLineToolDecompilers)
The (new, in 5.1.0.x) checks in org.apache.tapestry5.ioc.internal.DefaultModuleDefImp mean that a module implemented in Scala throws an exception on load:
java.lang.RuntimeException: Module class <MODULE_NAME> contains unrecognized public methods: public static final int <MODULE_NAME>.$tag() throws java.rmi.RemoteException.
It would be nice to have a way to work around this so that Scala could be used with Tapestry IOC 5.1.0.x (including Modules). One generic approach may be to have an @IgnoredPublicMethods annotation applicable to Module classes that took an array of Strings that named methods that should also be removed from the "methods" set before checking whether there are superfluous public methods. Of course, there's always the hard-code exception too (ugly but a lot less "investment" for this pesky incompatibility).
As an example, the following article describes Scala and Tapestry: http://fanf42.blogspot.com/2009/02/tapestry-5-scala-view-article-in-html.html. If you checkout the git project and update the Tapestry release version to 18.104.22.168, you'll see it fail, where in 5.0.x it worked.
The relevant code is:
109 // Want to verify that every public method is meaningful to Tapestry IoC. Remaining methods might
110 // have typos, i.e., "createFoo" that should be "buildFoo".
112 Set<Method> methods = CollectionFactory.newSet(moduleClass.getMethods());
116 boolean modulePreventsServiceDecoration = moduleClass.getAnnotation(PreventServiceDecoration.class) != null;
118 grind(methods, modulePreventsServiceDecoration);
119 bind(methods, modulePreventsServiceDecoration);
121 if (methods.isEmpty()) return;
123 throw new RuntimeException(String.format("Module class %s contains unrecognized public methods: %s.",