plugin-gradle: Build shadow jar and relocate jgit

[rickard-von-essen]

This builds a shadow jar with all dependencies bundled in the plugin and relocates most dependencies jgit under shadow. This will fix issues where other Gradle plugins uses incompatible versions of the same dependencies.

Fixes #587

[rickard-von-essen]

I'll do some further testing before this is ready.

[Goooler]

Using relocationPrefix "shadow" might be enough?

[rickard-von-essen]

(together with enableRelocation = true)

I got some issues with loading some of the dependencies, like this:

Execution failed for task ':tasks'.
> Could not create task ':spotlessGroovyGradle'.
   > java.io.IOException: Failed to load eclipse groovy formatter: java.lang.RuntimeException: java.lang.ClassNotFoundException: shadow.equo.solstice.p2.P2QueryResult

So I backed out of relocating most deps and instead focused on JGit only.

[Goooler]

I tried this on my fork, it works well. if I missing something? See Goooler#15.

[nedtwigg]

Did you test the Greclipse formatter? I would expect the Eclipse-based formatters to fail.

[Goooler]

That should be included in Maven tests on CI? Do I need some extra running?

[nedtwigg]

I think the Gradle and Maven integration tests are not testing against the shadowed jar. I think you have to publish to maven local to test that. Changing the PR so that at least one of the Gradle or Maven integration tests is testing using the shadowed jar would be a great way to prove me wrong.

I'm willing to merge this without such a test, but only if I can understand how it is working. I would expect the eclipse-based formatters should be "unshadeable", and shading them without changing their packages creates really painful bugs.

[Goooler]

Yeah, will try to add integration tests for using shadow jar.

[rickard-von-essen]

This works for me™️

[nedtwigg]

I think that everything that gets embedded should have a prefix, relocationPrefix 'spotless.shadow'.

If JGit is the problematic dep, it could be just these that get embedded

• spotless-lib
• spotless-lib-extra
• jgit

Or include everything except the org.eclipse & equo, and leave the others out?

[rickard-von-essen]

So I updated this to now:

• Bundle JGit and it's deps
• Bundle com.diffplug.durian:* and it's deps
• Relocate org.eclipse.jgit into spotless.shadow.org.eclipse.jgit
• Include spotless-lib and spotless-lib-extra normal deps, since they include all deps that are problematic to bundle.

The built plugin works and resolves the issues with clashing JGit versions between plugins, but this breaks almost all tests in plugin-gradle with this error:

java.lang.NoClassDefFoundError: com/diffplug/spotless/Jvm

And I couldn't figure out how to resolve that 😞

[nedtwigg]

If we shade a transitive (like JGit), we have to shade all the code which calls into it (spotless-lib-extra) so that lib-extra can updated to look for shadow.jgit.

The problem is that there are some dependencies (like everything related to Eclipse) which use reflection, so those cannot be shaded because it breaks the reflection.

A quick workaround is to shade eclipse/equo stuff, but have them not have prefixes. That will blow up fast, because if the "real" jars are on the classpath from another plugin, we will get truly horrific errors, because it's random which classfiles will end up getting used.

If you can shade spotless-lib-extra and jgit without shading all of the others, we would be in business. One hacky way I can imagine doing something like this:

• shade spotless-lib-extra and all its dependencies
• prefix for spotless-lib-extra is shadow.spotlessextra
• prefix for jgit is shadow.jgit
• no prefix for everything else
• then, in the classfile, remove every class except shadow.*
• then, in the pom, add back the jars we need that got removed by shadow

[nedtwigg]

• I think this is what we need, but for only jgit Partial ConfigureShadowRelocation task johnrengelman/shadow#330