> Can you get here with a name that doesn't originate from Scala source? 

Yes

> Technically you should try to avoid decoding them. We had a bug recently where a Java class named R$attr broke the compiler. Maybe it's not the most important thing for MiMa.

Bugs are just part of software development, so I'm not really worried about that. The alternative would be to duplicate the logic, as I still want to use the decoded name for error reporting purposes. But the actual main reason for using decoded names, is that [PackageInfo.isAccessible](https://github.com/dotta/migration-manager/blob/5bfde65f3edad4dadd7eecbb9a0b4cc37a350c74/core/src/main/scala/com/typesafe/tools/mima/core/PackageInfo.scala#L74) relies on it.