Bug 112490 Patch to fix the mess I made
I have done bad things. I now prostrate myself and humbly ask that some gracious soul submit this patch (which I will attach forthwith) so that I may redeem myself. Basically, I (well really John but I made him do it) moved the ResourceMapping stuff to API but we missed a few things that needed to be done, causing great grief to the JDT team. Please spare the lashes as I have a low pain threshold.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/ide/model/WorkingSetAdapterFactory.java
}
            }
            if (resourceAdapter instanceof IContributorResourceAdapter) {
                
                IResource resource = ((IContributorResourceAdapter)resourceAdapter).getAdaptedResource(element);
                if (resource != null) {
                    Object mapping = internalGetAdapter(resource, ResourceMapping.class);
                    if (mapping instanceof ResourceMapping) {
                        return (ResourceMapping)mapping;
                    }
                }
            }
        }
        return null;
    }
    
      Object internalGetAdapter(Object o, Class adapter) {
        if (o instanceof IAdaptable) {
            IAdaptable element = (IAdaptable) o;
            Object adapted = element.getAdapter(adapter);
            if (adapted != null)
                return adapted;
        }
        
         
        
        return Platform.getAdapterManager().getAdapter(o, adapter);
    }
}