CDI: Investigate behavior of @Alternative annotation in conjunction with @Priority(1)

Problem

• In the engine-cdi test suite, with ProgrammaticBeanLookupTest a test exists that tests if an alternative bean can be selected using the @Alternative annotation.
• The only way to select an alternative bean implementation in CDI 1.0 is to declare the bean via the META-INF/beans.xml file [1].
• In Quarkus, the content of the META-INF/beans.xml file is ignored, which means that it is not possible to select an alternative bean implementation via this file.

Solution

What Quarkus supports to specify an alternative bean implementation:

• From CDI 1.1 onwards, it is possible to define an alternative implementation programmatically via @Priority(int) annotation [3].
• Since @Priority cannot be used for producer methods, Quarkus offers the custom annotation io.quarkus.arc.AlternativePriority.
• It is possible to select an alternative bean implementation via Quarkus application.properties file and the property quarkus.arc.selected-alternatives.

You can read more about it in the official Quarkus documentation [4].

Decision

• Since our engine-cdi module doesn't make use of the @Alternative annotation, we don't need to document the alternative solutions.
• We exclude the failing ProgrammaticBeanLookupTest in the Quarkus test suite and introduce a dedicated test [5] that ensures the behavior expected in Quarkus.

[1] https://docs.jboss.org/weld/reference/1.0.0/en-US/html_single/#alternatives
[2] https://quarkus.io/guides/cdi-reference#declaring-selected-alternatives
[3] https://docs.jboss.org/weld/reference/2.2.0.Final/en-US/html_single/#alternatives
[4] https://quarkus.io/guides/cdi-reference#declaring-selected-alternatives
[5] https://github.com/camunda/camunda-bpm-platform/blob/master/quarkus-extension/engine/deployment/src/test/java/org/camunda/bpm/quarkus/engine/test/lookup/ProgrammaticBeanLookupTest.java