@amiracam I'm not sure if anyone has tested the plugin with Gradle 4 yet. I'm pretty sure it works with Gradle 3. You may want to open an issue on Github and include a gist of the error you're getting.
@amiracam Are you sure it's using Gradle 4? They don't have an actual release for 4 yet, just a milestone.
@amiracam First, you need to decide which of the plugins you're actually going to use: the jar plugin, the war plugin, or just the base plugin (this is only really appropriate if you're only running Ruby through gradle).
@amiracam besides the basics of adding the plugin as a buildscript dependency, applying the plugin to the gradle file, and then defining the appropriate jrubyJar or jrubyWar configurations, there's no "one correct way" to use it.
it's flexible enough to be applicable in most deployment scenarios.
I use it to create an artifact jar with just jruby, my rubygem and jar dependencies, and run jruby directly using that artifact jar against the ruby files that are deployed directly on the filesystem.
I gather that most people include a "from" line in their jrubyJar config to include their ruby files in the jar, and also add a custom entrypoint to create a self-contained executable jar with all their code in it.