My scenario is the following:
I have an @Alternative MockMailService class which should only be used during testing to not send out 5k mails to customers and employees when running the unit and integration test suite.

@Alternative
@ApplicationScoped
@Exclude(ifProjectStage=Production.class)
public class MockMailService implements MailService {...}

Of course I only need to activate it in beans.xml:

<beans>
  <alternatives>
    <class&gt;org.acme.MockMailService</class&gt;
  </alternatives>
</beans>

This is perfectly fine in CDI 1.0 but might be interpreted as not be allowed in the CDI 1.2 wording paragraph 5.1.1.2. "Declaring selected alternatives for a bean archive".

Please note that we introduced a check in CDI 1.0 purely to help the customer eagerly detect possible wrong configuration. E.g. if he simply has a typo in the classname. It was not intended to restrict useful use cases!

What the intention was: all is fine IF one of

• There exists a class T with the given name
• That class T (or a contained producer field or producer method) is annotated with @Alternative
• There is a Bean<T> with isAlternative() == true