Description Nicolas Rouquette 2010-05-28 23:21:05 EDT

For the last ballot for UML 2.4 ending in 3 days from now, I have created many diagrams with RSA 7.5 for UML's infrastructure & superstructure. 
I've done dozens of package merges with the help of the fix  https://bugs.eclipse.org/bugs/show_bug.cgi?id=313837

I was in package merge heaven until I updated the model to reflect the resolution for OMG issue 13993: http://www.omg.org/issues/issue13993.txt
The resolution we just finished today involves separating PrimitiveTypes from the InfrastructureLibrary, thus requiring updating all of the package merge maps. 
Now, all package merges fail, including the simplest of all, L0

The problem is subtle but it's been out in the open for several years in:
org.eclipse.uml2.uml.util.UMLUtil.PackageMerger.merge(Package, Map<String, String>, DiagnosticChain, Map<Object, Object>)


		public Map<EObject, List<EObject>> merge(
				org.eclipse.uml2.uml.Package package_,
				Map<String, String> options, DiagnosticChain diagnostics,
				Map<Object, Object> context) {
			receivingPackage = package_;

			mergedPackages = getAllMergedPackages(package_);

			copyAll(mergedPackages);
			copyReferences();

			receivingPackage.getPackageMerges().clear();

			if (options != null) {
				processOptions(options, diagnostics, context);
			}

			return resultingToMergedEObjectMap;
		}
		
As written, the code implicitly assumes that clearing the Package::receivingPackage  collection will be enough to delete the PackageMerge relationships. As long as we've been merging UML infrastructure/superstructure that had no diagrams this code didn't create any problems because by removing the unique in a model to a PackageMerge element was enough to effectively delete it from the model. Since we've been using RSA 7.5 to do the diagrams and RSA uses the GMF notation metamodel to store diagrams as instances of the notation metamodel, every element/relationship in the model shown in a specific diagram has an extra reference from the GMF node/edge showing the element/relationship.

When an RSA diagram shows a package merge relationship from the model, the extra reference to the UML::PackageMerge relationship due to the GMF edge object is enough to alter the behavior of the code above where the UML::PackageMerge element is no longer deleted from the model but left dangling without being logically part of the extent of the model. 

To experience this problem, load the models attached: InfrastructureLibrary.uml, PrimitiveTypes.uml and L0.uml.
Open L0.uml and merge the L0 package with default options.

Then, try to save the model; this will trigger a Dangling HREF exception. 

Before saving, you can also try to validate the model; this time, you'll get a cleaner message about a GMF edge object having a dangling reference to a package merge relationship.

With the simple attached patch, everything works properly. Of course, the diagram in the merged model have lost their reference(s) to the PackageMerge elements that have been deleted but that is to be expected.