How to determine unused design files in Quartus

It should say "Can't find file..." if the file doesn't exist, so if there are any pointers to non-existing files, those are easy. I'm not sure of anything that says a file was read in but not used. You could move all the source so none of it is found, then when it complains about not finding what it needs(it will start with the top-level) copy them back over to where they should be. Would work if its tens of files, but probably not worth the effort if you have hundreds of files.

Under Analysis & Synthesis report is a section called Source Files Read, and it has a column called Used in Netlist. This seems like it would be what you want, but when I added a small file that doesn't get used, it doesn't show up in this list with an N(to say it's not used). Instead, it doesn't show up at all. You could probably use that information to compare against files being read in, but again, something of a manual process.