Xtend: fixed strange error message for void as a field type

[LorenzoBettini]

Closes #2877

[LorenzoBettini]

Of course, it fails until #2878 is merged

[LorenzoBettini]

@szarnekow I rebased the PR, which is now ready to review

[szarnekow]

I see that the message was take from JDT. In Xbase, we use

@Check
	public void checkTypeReferenceIsNotVoid(XExpression expression) {
		for (EObject eObject : expression.eContents()) {
			if (eObject instanceof JvmTypeReference) {
				JvmTypeReference typeRef = (JvmTypeReference) eObject;
				if (isPrimitiveVoid(typeRef)) {
					if (typeRef.eClass() == TypesPackage.Literals.JVM_PARAMETERIZED_TYPE_REFERENCE) {
						if (!((JvmParameterizedTypeReference) typeRef).getArguments().isEmpty()) {
							continue;
						}
					}
					error("Primitive void cannot be used here.", typeRef, null, INVALID_USE_OF_TYPE);
				}
			}
		}
	}

and in common.types

	protected void checkNotPrimitive(JvmTypeReference jvmTypeReference) {
		if (primitives.isPrimitive(jvmTypeReference)) {
			error("The primitive '"+jvmTypeReference.getQualifiedName('.')+"' cannot be a type argument", jvmTypeReference, null, IssueCodes.INVALID_USE_OF_TYPE);
		}
	}

All not super aligned with each other. Maybe keep it somewhat consistent and use Primitive void is an invalid type for the field ...

[LorenzoBettini]

@szarnekow OK, I'll change it to Primitive void is an invalid type for the field and then merge it, OK?

[LorenzoBettini]

@szarnekow , I checked other points in the XtendValidator:

	@Check
	public void checkXtendParameterNotPrimitiveVoid(XtendParameter param) {
		if (isPrimitiveVoid(param.getParameterType())) {
			XtendFunction function = (XtendFunction) (param.eContainer() instanceof XtendFunction ? param.eContainer()
					: null);
			if (function != null)
				error("void is an invalid type for the parameter " + param.getName() + " of the method "
						+ function.getName(), param.getParameterType(), null, INVALID_USE_OF_TYPE);
			else
				error("void is an invalid type for the parameter " + param.getName(), param.getParameterType(), null,
						INVALID_USE_OF_TYPE);
		}
	}

we always use that form "void is an invalid type for..." also in other parts:

So, shall I leave it like that?