[Architecture Board] Clean up SPI to provide implementations

Many MP specs provide an SPI for implementations to provide implementations of some API interfaces. Usually, the following pattern is used:

• CoreInterface interface in the root API package
• a CoreInterfaceResolver abstract class in an SPI package
• a static resolver method which provides a default CoreInterface instance
• the resolver method uses the service loader mechanism to load a CoreInterfaceResolver implementation which provides an instance of CoreInterface
• alternatively, CoreInterfaceResolver implementation can also be set globally with a static setInstance method (to simplify providing an implementation in an OSGi environment)

Several issues have been raised to remove the setInstance method from the API artifact, claiming that separating it into an SPI package within the same artifact isn’t enough to prevent API consumers using it: https://github.com/eclipse/microprofile-rest-client/issues/103, https://github.com/eclipse/microprofile-open-api/issues/224, https://github.com/eclipse/microprofile-config/issues/364

[struberg]

No @rmannibucau the link @starksm64 posted is the setInstance method. Afaiu this merhod is not needed anymore, nowhere. Not even in mp-config. It is purely for ancient OSGi containers and not needed anymore with more modern OSGi service discovery. We should clarify this with a few OSGi experts and have them provide feedback.

The point you likely mean is that mp-config is probably a rare example which cannot be CDI-first as it is needed during container startup already. This is actually a separated topic and we should split those 2 up in 2 tickets.

[kenfinnigan]

In today’s architecture meeting there was agreement that this issue can now be closed