I asked for similar question jetty-jndi-resource-fails using Jetty only, which is described by Jetty documentation as Jetty: startup-classpath.
Now I like to use "Module specified Libraries" and setup it over Gretty as repository dependencies. I didn't find anything like this in Getty doc: Gretty-configuration. I also search Gretty: integratin-test Git for any usable example, but without result.
Is this Jetty feature unsupported over Gretty? Or is possible to setup the --module=ext parameter anyhow? Could anyone using :farmRun let me know how to handle the server provided external libs shared over multiple web applications in farm any clear way?
The "module specific libraries" that you are referring to are for the standalone version of Jetty.
If you see references to ${jetty.home} and ${jetty.base} concepts, and access to the jetty-home artifact (or the older jetty-distribution artifact) then you are working with a technology that uses the standalone version of Jetty.
Based on the Gretty documentation you have linked, it does not appear that Gretty uses the standalone version of Jetty, but rather the embedded-jetty (all in code) techniques to start Jetty.
The fact that Gretty has an optional XML startup feature means very little, as that XML is really just code to configure a object in their embedded-jetty setup, no different then having an interpreted script (in groovy or jsh) to accomplish the same thing. There are no modules when using this Gretty setup.