This is a simple addition of a few lines to echo the status of the dashboard-single.xml files.
I would prefer an error message instead, if the file was not found. But using the Jelly docs, I could not find out how.
This on the surface is a trivial thing, but until I finally dug in and added tons of debug echo statements like this to track down what the problem was, I was clueless as to the problem why the Dashboard page was blank. This echo change was the one I needed, so I think it may help others in the same situation.
I also wondered about adding a maven.dashboard.debug (or msglevel) property and surrounding a bunch of them, but I am not sure of desire and I am way out of time for now!
As a side note, the problem was the dashboard-single.xml files were not created in the subprojects. All the debug statements led me to that in the flow.
The fix was to do the opposite of what the docs say and change the order of the goals from
maven.multiproject.site.goals=site,dashboard:report-single
to
maven.multiproject.site.goals=dashboard:report-single,site
Tracing through the jelly execution, I saw where the xml file was created and reversed them to make it work.
Makes me wonder how it even works for others having it in the order the docs say!
The new echo statements.