generate method is either called by maven-site-plugin, either called by another plugin that wants to generate report independently from maven-site-plugin
which plugin other than maven-site-plugin generates reports?
the only case I know of is the plugin itself, to be able to invoke the standalone report without whole site: this case is implemented in reporting implementation, with a call to the MavenMutiPageReport API
I don't find any practical cases needing this warning.
On the other hand, I know that maven-site-plugin < 3.0-beta-1 can't call the new API because of classloading issues (MavenPultiPageReport interface is not in Maven core classloader, but loaded separately for every reporting plugin)
Then this warning has only drawbacks to IMHO
done in r960042