I'm working on a Grails plugin whose main contribution is a taglib. In Grails 3.1.11 it worked ok. I also have a simple Grails app just for testing the plugin. Enter Grails 3.2.2.
After migrating plugin and app to 3.2.2 the plugin shows no signs of life. The plugin doWithApplicationContext closure is no longer executed at app startup. The taglib is not found by gsp:s. I did the migration by creating a new plugin and app with Grails 3.2.2 and then fill in the sources.
Sorry for this vague question, but what strings should I pull to find out what's wrong?
Edit 1: Yes, I did the sanity check to have the app depend on a non-existing version of the plugin and got the expected conflict. So it's not that the plugin is totally decoupled from the app.
Edit 2: After setting DEBUG logging on packages grails.plugins and org.grails.plugins a warning message appeared. It came from org.grails.plugins.CorePluginFinder. It couldn't find the plugin descriptor (...Plugin.groovy). I examined the plugin jar, found the plugin descriptor class in a file hierarchy rooted in BOOT-INF. Clearly the plugin loader didn't look into that hierarchy. I thought I was seeing a Grails bug because I didn't know about Boot repackaging. I added a post here to that effect, but after getting Graeme's answer I deleted the post because it detracted attention.
What you are seeing is that if you run gradle assemble on a plugin then the bootRepackage task is run which re-packages the plugin JAR as a runnable JAR which is not what you want when you plan to use the plugin from an application.
If you simply run gradle publish or gradle publishToMavenLocal or gradle jar then you get the JAR file that has not been re-packaged by Boot. As far as I am aware this is not a change from Grails 3.1.
You can also disable Boot repackaging all together in the plugin build.gradle if you never plan to use the plugin as an actual application or runnable JAR file:
bootRepackage.enabled = false