[MS30] Fix API compatibility issues

[ppkarwasz]

Since we had to abandon the Revapi Maven Plugin around version 2.17.2 due to incompatibilities with other Maven plugins, we do not have a way to automatically check for breaking API changes.

We need to introduce other tools to guarantee a stable API.

Possible candidates:

• japicmp,
• bnd-baseline-maven-plugin.

[garydgregory]

What about japicmp?

[ppkarwasz]

What about japicmp?

I added a list of candidates to the initial comment that we will evaluate in due time.

In version 2.21.0 I gave bnd-baseline-maven-plugin a test run. I am quite satisfied with the results. Also the two feature requests I submitted (bndtools/bnd#5792 and bndtools/bnd#5808) were granted in a very prompt manner. For the definitive decision we should probably also considerate the community that stands behind the tool.

[ppkarwasz]

Over the past year the BND Baseline plugin prevented breaking API changes many times, e.g.:

• fe92961
• 9f576e1
• f0e82d1
• 9565d4b
• b8cb35f

The only currently known limitation of the BND Baseline check is the case of the multi-release modules (log4j-api-java9 and log4j-core-java9), because only their Java 8 equivalents are tested for API compatibility. We briefly explored the idea of using BND's multi-release support (cf. apache/logging-parent#93), but we decided to disable it (cf. apache/logging-parent#96), since it introduces a lot of complexity to the built artifacts.
I believe that commits like 945cbc8 should be enough for our use case, where we have only a couple of classes compiled against Java 9.

[ppkarwasz]

I tried japicmp and it can be useful to compare two already published JARs (I used this in #3339).
Otherwise it does not seem to offer anything that the BND Baseline plugin does not offer and BND seems to be maintained by a larger group of developers.
I would stick with BND.