// Eine Strukturdefinition
Type:
    'type' name = ID 
        ('extends' superType = [Type|QualifiedName])? '{'
    '}'
;

  public static final String  INHERITANCE_LOOP = "inheritance-loop";
  @Check
  public void checkTypeInheritance(Type type) {
    Type hierarchyLoopElement = getHierarchyLoop(type);
    if (hierarchyLoopElement != null) {
      error('Cycle detected ...',
            MyDslPackage.Literals.TYPE__SUPER_TYPE, INHERITANCE_LOOP, hierarchyLoopElement.getName());
    }
  }

  @Fix(MyDslJavaValidator.INHERITANCE_LOOP)
  public void breakInheritenceLoop(...) {
    acceptor.accept(issue, 
        "..", "..", "..", 
        new IModification() {          
          @Override
          public void apply(IModificationContext context) throws Exception {
            IXtextDocument xtextDocument = context.getXtextDocument();
            xtextDocument.replace(issue.getOffset(), issue.getLength(), "");
          }
        });
  }

final IXtextDocument xtextDocument = context.getXtextDocument();
xtextDocument.readOnly(new IUnitOfWork.Void<XtextResource>() {
  public void process(XtextResource state) throws Exception {

    logger.debug("Trying to remove inheritance");
    
    EObject affectedObject = state.getEObject(issue
        .getUriToProblem().fragment());
    
    if (affectedObject != null) {
      
      int extendsStart = -1;
      int extendsEnd = -1;
      
      logger.debug("Searching for range to be removed");
      
      Iterable<INode> children = NodeModelUtils.getNode(
          affectedObject).getAsTreeIterable();
      
      for (INode child : children) {
        
        if (child instanceof AbstractNode) {
          AbstractNode node = (AbstractNode) child;
          boolean isKeyword = (node.getGrammarElement() instanceof Keyword);
          boolean isCrossReference = (node.getGrammarElement() instanceof CrossReference);

          // first try to find the extends keyword, then the following crossreference
          if (isKeyword
              && "extends".equals( ((Keyword)node.getGrammarElement()).getValue())) {
            extendsStart = node.getTotalOffset();
            logger.debug("Found 'extends' at position: " + extendsStart + ", now searching for crossreference");
          }
          else if (extendsStart > 0 && isCrossReference) {
            extendsEnd = node.getTotalEndOffset();
            logger.debug("Found CrossReference at position: " + node.getTotalOffset());
          }

          // as we have found them we can replace the code and finish
          if (extendsStart > 0 && extendsEnd > 0) {
            logger.debug("extends and crossreference found, remove from " + extendsStart + " to " + extendsEnd);
            xtextDocument.replace(extendsStart, extendsEnd - extendsStart, "");
            return;
          }
        }
      }
    }
    else
    {
      logger.debug("No object found to remove inheritance");
    }
  };
});

org.eclipse.emf.common.util.WrappedException: java.lang.RuntimeException: The context 'Model' is not valid for type 'Struct'
Recommended contexts for type 'Struct': Declaration, TypeDeclaration, Struct, StructElement, UnionElement
The context 'Model' is valid for types: ModelDeclaration

Semantic Object: ModelDeclaration'INHERITANCE'.declarations[4]->Struct'ERR1_A'
	at org.eclipse.xtext.ui.editor.quickfix.IssueResolution.apply(IssueResolution.java:50)
	at org.eclipse.xtext.ui.editor.quickfix.QuickAssistCompletionProposal.apply(QuickAssistCompletionProposal.java:32)
	at org.eclipse.jface.text.contentassist.CompletionProposalPopup.insertProposal(CompletionProposalPopup.java:935)
...
Caused by: java.lang.RuntimeException: The context 'Model' is not valid for type 'Struct'
Recommended contexts for type 'Struct': Declaration, TypeDeclaration, Struct, StructElement, UnionElement
The context 'Model' is valid for types: ModelDeclaration

Semantic Object: ModelDeclaration'INHERITANCE'.declarations[4]->Struct'ERR1_A'
	at org.eclipse.xtext.serializer.diagnostic.ISerializationDiagnostic$ExceptionThrowingAcceptor.accept(ISerializationDiagnostic.java:66)
	at at.mydsl.serializer.AbstractMyDslSemanticSequencer.createSequence(AbstractMyDslSemanticSequencer.java:623)
	at org.eclipse.xtext.serializer.impl.Serializer.serialize(Serializer.java:68)