Support a full shrinking mode in for UnusedTracker using R8

[netomi]

This is a suggestion for an improvement to an existing feature of this awesome gradle plugin.

The current minimize feature is relatively simple and is not able to shrink all unused classes from 3rd party libraries. For my own use-case this was not sufficient, having a full shrinking support together with relocation re-use of a lot of classes not available as stand-alone jars / classes would be much easier (that was actually my use-case, I wanted to use single classes from large jars without copying the content).

The shadowJar plugin has already all the features that you need for this purpose, it just lacks support for a full shrinker like ProGuard or R8. ProGuard is unfortunately GPL so I decided to provide a version of the UnusedTracker class that uses R8 for doing the dirty work.

Please take a look at my pull request. I tested it with various projects (even with the R8 project itself) and it works pretty fine. I am open to suggestions and improvements. The current integration was a quick and dirty proof of concept.

I would be happy if the feature request would be accepted.

The pull request currently uses the latest dev version of R8 which is not yet available on the normal google maven repo.

[netomi]

I have added a demonstration of this pull request to this branch of my project:

https://github.com/netomi/uom/tree/shadow-dependencies

It pulls 1 class from hibernate-validator and uses 1 method from guava:

• ConcurrentReferenceHashMap
• Suppliers.memoize

with the original minimize feature many more classes would be shadowed, like annotation classes for code in guava ....

With the use of R8 this can be greatly reduced, only necessary classes are shadowed which would allow me to use this functionality rather than copying or rewriting the code when you dont want to pull in such a big dependency.

[gildor]

@netomi Maybe this issue and #566 would be accepted if use a bit different approach: Extract UnusedTrackerWithR8 to own dependency (or better a Gradle plugin, it's more flexible, allows configure custom tasks and provide extensions DSL), contribute to ShadowCopyAction.groovy only parts required to provide custom tracker using shadow plugin public api which allows specifying custom UnusedTracker (it may be as simple as providing a factory for UnusedTracker)

I believe this feature has a great potential, especially if it would be possible to configure r8 with proguard config file.

If all required APIs on ShadowPlugin would be in place and it would be possible to provide custom UnusedTracker it makes it easier to try R8 and do not depend on ShadowPlugin release cycle

[netomi]

Your comment makes sense. I am willing to update the PR to take your comments into account. My first version was a proof-of-concept to see if there is general interest in this idea. It should be changed to be able to select different shrinking modes and to select custom configuration as needed for tools like R8 / Proguard.

[StragaSevera]

@netomi Is there any update on this feature? It would be ultra-cool to have the ability to use minimization from ShadowJar =-)

[netomi]

Its a nice feature imho, so far I did not get any feedback from the maintainer of the plugin, but I am willing to update my PR if there is interest to integrate it.