Compactify names when flattening, to limit length of classfile names

This is intended to replicate the behavior of Scala 2.13, where
classfile names are limited to 240 characters.

Author: griggt

compiler/src/dotty/tools/dotc/core/SymDenotations.scala

@@ -480,7 +480,8 @@ object SymDenotations {
           // duplicate scalac's behavior: don't write a double '$$' for module class members.
           prefix = prefix.exclude(ModuleClassName)
         def qualify(n: SimpleName) =
-          kind(prefix.toTermName, if (filler.isEmpty) n else termName(filler + n))
+          val qn = kind(prefix.toTermName, if (filler.isEmpty) n else termName(filler + n))
+          if kind == FlatName then qn.compactified else qn
         val fn = name replace {
           case name: SimpleName => qualify(name)
           case name @ AnyQualifiedName(_, _) => qualify(name.mangled.toSimpleName)

tests/pending/run/t8199.scala renamed to tests/run/t8199.scala

@@ -44,7 +44,6 @@ object Test extends App {
   }
   def checkCallerImplClassName(): Unit = {
     val name = Thread.currentThread.getStackTrace.apply(2).getClassName
-    assert(name.contains("$class"))
     Test.checkClassName(name)
   }