Working on #9478

A functional test:
grails/grails3-functional-tests@45e2c10f647036
03d97840f9822e0f396c634726

Author: jeffscottbrown

grails-core/src/main/groovy/grails/core/GrailsControllerClass.java

@@ -120,4 +120,6 @@ public interface GrailsControllerClass extends InjectableGrailsClass {
      * @param urlConverter The {@link grails.web.UrlConverter} to register
      */
     void registerUrlConverter(UrlConverter urlConverter);
+
+    String actionUriToViewName(String actionUri);
 }

grails-core/src/main/groovy/org/grails/core/DefaultGrailsControllerClass.java

@@ -51,7 +51,8 @@ public class DefaultGrailsControllerClass extends AbstractInjectableGrailsClass
     private Map<String, FastMethod> actions = new HashMap<String, FastMethod>();
     private String defaultActionName;
     private String namespace;
-
+    protected Map<String, String> actionUriToViewName = new HashMap<String, String>();
+    
     public DefaultGrailsControllerClass(Class<?> clazz) {
         super(clazz, CONTROLLER);
         namespace = getStaticPropertyValue(NAMESPACE_PROPERTY, String.class);
@@ -150,6 +151,7 @@ public boolean mapsToURI(String uri) {
     @Override
     public void registerUrlConverter(UrlConverter urlConverter) {
         for (String actionName : new ArrayList<String>(actions.keySet())) {
+            actionUriToViewName.put(urlConverter.toUrlElement(actionName), actionName);
             actions.put( urlConverter.toUrlElement(actionName), actions.remove(actionName));
         }
     }
@@ -170,4 +172,9 @@ public Object invoke(Object controller, String action) throws Throwable {
         return handle.invoke(controller, EMPTY_ARGS);
     }
 
+    public String actionUriToViewName(String actionUri) {
+        String actionName = actionUriToViewName.get(actionUri);
+
+        return actionName != null ? actionName : actionUri;
+    }
 }

grails-web-url-mappings/src/main/groovy/org/grails/web/mapping/mvc/UrlMappingsInfoHandlerAdapter.groovy

@@ -97,7 +97,8 @@ class UrlMappingsInfoHandlerAdapter implements HandlerAdapter, ApplicationContex
                     return (ModelAndView) modelAndView
                 }
                 else if(result instanceof Map) {
-                    return new ModelAndView(action, new HashMap<String, Object>((Map)result))
+                    String viewName = controllerClass.actionUriToViewName(action)
+                    return new ModelAndView(viewName, new HashMap<String, Object>((Map)result))
                 }
                 else if(result instanceof ModelAndView) {
                     return (ModelAndView) result