Bad interaction between -optimise and generic signature generation

[odersky]

Assuming #3602, if I compile tests/pos-no-optimise/escaping-refs.scala with -optimise (and -uniqid for debugging), I get:

java.lang.AssertionError: assertion failed: bad parameter reference Bar#6061.this.B11#3739 at erasure
the parameter is type B11#3739 in class Bar#3738 but the prefix Bar#6061(Bar#6061.this)
does not define any corresponding arguments.
        at scala.Predef$.assert(Predef.scala:219)
        at dotty.tools.dotc.core.Types$NamedType.argDenot(Types.scala:1741)
        at dotty.tools.dotc.core.Types$NamedType.fromDesignator$1(Types.scala:1669)
        at dotty.tools.dotc.core.Types$NamedType.computeDenot(Types.scala:1690)
        at dotty.tools.dotc.core.Types$NamedType.denotAt(Types.scala:1641)
        at dotty.tools.dotc.core.Types$NamedType.denot(Types.scala:1630)
        at dotty.tools.dotc.core.Types$NamedType.info(Types.scala:1624)
        at dotty.tools.dotc.core.Types$Type.dealias(Types.scala:981)
        at dotty.tools.dotc.core.Types$Type.dealias(Types.scala:1012)
        at dotty.tools.dotc.core.Types$Type.widenDealias(Types.scala:1016)
        at dotty.tools.dotc.transform.GenericSignatures$.boxedSig$1(GenericSignatures.scala:59)
        at dotty.tools.dotc.transform.GenericSignatures$.argSig$1(GenericSignatures.scala:149)
        at dotty.tools.dotc.transform.GenericSignatures$.$anonfun$javaSig0$8(GenericSignatures.scala:176)
        at dotty.tools.dotc.transform.GenericSignatures$.$anonfun$javaSig0$8$adapted(GenericSignatures.scala:176)
        at scala.collection.immutable.List.foreach(List.scala:389)
        at dotty.tools.dotc.transform.GenericSignatures$.classSig$1(GenericSignatures.scala:176)

The problem seems to be that there is a reference Bar.this.B11 where B11 is a type parameter of a different Bar. To track this down, I instrumented the apply method in object TypeRef in Types.scala as follows:

object TypeRef {
/** Create a type ref with given prefix and name */
def apply(prefix: Type, desig: Designator)(implicit ctx: Context): TypeRef = {
  desig match {
    case sym: Symbol if sym.is(ClassTypeParam) && sym.name.toString == "B11" =>
      prefix match {
        case prefix: ThisType if prefix.cls.name.toString == "Bar" =>
          assert(prefix.cls == sym.owner, i"$prefix . $desig")
        case _ =>
      }
    case _ =>
  }
  ...

This fails with an error in changeOwner, called from simplify.

[allanrenucci]

Closing as we removed local optimisations in #4799 and this is now properly tested (i.e. the test was moved to pos from pos-no-optimise)