Integrate eclipse transformer with Batavia

[ropalka]

https://github.com/eclipse/transformer

[ropalka]

It is not possible to integrate Eclipse transformer with Batavia project at the moment because both projects use different abstractions. Batavia's main abstraction is Resource - which is any entry inside jar file or any file on file system. The Eclipse transformer's abstraction is CLI and passing it configuration args. (FYI @jfdenise @scottmarlow)

[jfdenise]

Raw thinking, could we have an integration at a higher level to handle jar transformation only? Mainly at the Tools API level? Batavia would abstract the transformer in use. Galleon would still be able to select the transformer tools backend.

[ropalka]

What we could do is to modify Batavia project to be configurable similar way like Eclipse transformer is, that is we should introduce Option abstraction, TransformerBuilder.addOption(name, value) methods, maybe Changes abstraction including Transformer.getChanges() method?

[ropalka]

Our new abstractions would become Option and Change etc instead of Transformer.Resource
and we would move bunch of code from Tools API to Transformer API, WDYT @scottmarlow ?

[scottmarlow]

Our new abstractions would become Option and Change etc instead of Transformer.Resource
and we would move bunch of code from Tools API to Transformer API,
Do you mean to move bunch of code from Batavia Tools API to Eclipse Transformer API? I assume you mean Batavia Transformer API, as I don't see an API in Eclipse Transformer. I think that this idea is good, unless we can think of a way to change Eclipse Transformer to be easier to integrate with.

issues/28 is for moving the cli into its own project, to better support maven/gradle drivers. Should we stick to passing parameters the Eclipse Transformer CLI style interface way or do we want a better integration point than org.eclipse.transformer.Transformer#runWith?

[scottmarlow]

Raw thinking, could we have an integration at a higher level to handle jar transformation only? Mainly at the Tools API level? Batavia would abstract the transformer in use. Galleon would still be able to select the transformer tools backend.

If the question is could we remove ToolUtils#transformClassFile, I think we could, if that helps our integration with Eclipse Transformer.

[ropalka]

Our new abstractions would become Option and Change etc instead of Transformer.Resource
and we would move bunch of code from Tools API to Transformer API,
Do you mean to move bunch of code from Batavia Tools API to Eclipse Transformer API? I assume you mean Batavia Transformer API, as I don't see an API in Eclipse Transformer. I think that this idea is good, unless we can think of a way to change Eclipse Transformer to be easier to integrate with.

issues/28 is for moving the cli into its own project, to better support maven/gradle drivers. Should we stick to passing parameters the Eclipse Transformer CLI style interface way or do we want a better integration point than org.eclipse.transformer.Transformer#runWith?

It looks like Eclipse transformer is little bit behind us WRT proper separation of tools vs. transformer code. Anyway they are going to move the proper way.

[ropalka]

Raw thinking, could we have an integration at a higher level to handle jar transformation only? Mainly at the Tools API level? Batavia would abstract the transformer in use. Galleon would still be able to select the transformer tools backend.

If the question is could we remove ToolUtils#transformClassFile, I think we could, if that helps our integration with Eclipse Transformer.

Yes, that was the question @scottmarlow . It seems we have three options on table ATM :

1. short term - we adjust our API to be able to integrate via current Eclipse transformer CLI
2. middle term - wait little bit and see what will be the outcome of ISSUE-28
3. long term - participate on Eclipse project and adjust their API little bit to be better integrable with our API

[jfdenise]

With respect to integration in galleon I would vote for 2) and 3). Currently as soon as we have an eclipse transformer release that integrates the fix we need, I could release a galleon-plugins that calls into eclipse transformer directly. Then switching to use Batavia when ready would be an easy task.

[ropalka]

Initial Eclipse transformer integration is done. Thanks @scottmarlow for review, @jfdenise for valuable feedback.