Using a Java annotation as a ClassfileAnnotation leads to problems

[hrhino]

This one's mostly for fun, because why would you do such a thing?

hhoughton:tmp hhoughton$ scala-launch 2.12.6
Welcome to Scala 2.12.6 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_161).
Type in expressions for evaluation. Or try :help.

scala> @Deprecated class Foo
defined class Foo

scala> val ann = classOf[Foo].getAnnotation(classOf[Deprecated])
ann: Deprecated = @java.lang.Deprecated()

scala> ann: annotation.ClassfileAnnotation
java.lang.AssertionError: assertion failed:
  Cannot emit primitive conversion from Ljava/lang/Deprecated; to Lscala/annotation/ClassfileAnnotation; - <console>
     while compiling: <console>
        during phase: jvm

not a ClassCastException, as you may have thought!

I'm not sure what can be done about this; patching parents of a class to add superclasses that just aren't there at runtime is inviting runtime crashers at the very least.

[lrytz]

This is an endless source of bugs, see #9400. We should stop modifying java annotations (flags, parents, etc) and trying to work around the inconsistencies in later phases.

[hrhino]

ah, I think this is a duplicate of #9644, which I somehow didn't find.