DS 1.4 Component Property Types: Allow meta annotations or static fields for generating constant component properties

[bjhargrave]

Original bug ID: BZ#250
From: Konrad Windszus <kwin@apache.org>
Reported version: R7

[bjhargrave]

Comment author: Konrad Windszus <kwin@apache.org>

Sometimes it is desirable to use an annotation where a specific property is always supposed to have a specific value (i.e. is constant). Although it is possible to define that property via an annotation method with a default value, that way it could be overwritten by the user (which is not intended here).

To prevent that one could either allow component property annotations to be used as met a annotations or also interpret other static fields (apart from the already defined PREFIX) to end up as constant properties in the generated component descriptor.

For a concrete use case look at apache/sling-org-apache-sling-servlets-annotations#3.

[bjhargrave]

Comment author: Bertrand Delacretaz <bdelacretaz@apache.org>

I think this matches the behavior described in https://blog.osgi.org/2018/03/osgi-r7-highlights-declarative-services.html which says, in the "ComponentPropertyType" section:

For a marker annotation, a component property name is derived
from the component property type name, just as for single-element
annotations, and the component property value is Boolean.TRUE.
Marker annotations are only useful for setting a component property
to the value true.

[bjhargrave]

Comment author: Konrad Windszus <kwin@apache.org>

IMHO marker annotations are different i.e. they are just annotations without any methods. That wouldn't help here, as those only generate one single property. In our case we are interested to generate multiple properties out of a single annotation, where multiple dimensions should be dynamic and other should be static!