I have a large and Extremely Old (2013) Play application that kind of wound up largely trapped in amber for a decade (on Scala 2.11 and Play 2.5) due to dependency problems, which I'm currently speed-running up to reasonably modern spec. So far, I'm up to Scala 2.12 and Play 2.6.25. But I've hit a weird roadblock, and any suggestions would be very welcome.

The issue is that I finally turned on -Xfatal-warnings and -Ywarn-unused:imports. I worked my way through the thousand dead imports in the codebase, none of which were surprising.

But then I found that every single play template is producing an Unused import error on the @ sign for the parameter list at the top.

Searching around with Kagi, it sounds like this was a known issue for a while -- that Play was generating an unnecessary import, which was triggering this problem. But it also sounds like that was fixed, well before 2.6.25. So it's surprising, and I'm not sure what to do about it. I can't easily tell from the errors what specific import is causing the problem. (I'm on IntelliJ Community Edition; it isn't showing any of the imports in the generated .template files as unused, but I don't consider that authoritative.)

Any suggestions? I'm going to go try pulling in the silencer plugin, but that's a big and somewhat clumsy way to deal with the problem (assuming I can figure out all the knobs to get it to deal with this); I'd prefer a more nuanced solution if there is one.

(I'm kind of surprised by the problem in the first place, since it sounds like it had been found and fixed; any insights would be very welcome.)