SI-9331 Fix canEqual for case classes with HK type params

Time for the courage of our convictions: follow the advice of my
TODO comment from SI-8244 / f62e280825 and fix `classExistentialType`
once and for all.

This is the change in the generated `canEquals` method in the test
case; we no longer get a kind conformance error.

```
--- sandbox/old.log	2015-05-27 14:31:27.000000000 +1000
+++ sandbox/new.log	2015-05-27 14:31:29.000000000 +1000
@@ -15,7 +15,7 @@
       case _ => throw new IndexOutOfBoundsException(x$1.toString())
     };
     override <synthetic> def productIterator: Iterator[Any] = runtime.this.ScalaRunTime.typedProductIterator[Any](Stuff.this);
-    <synthetic> def canEqual(x$1: Any): Boolean = x$1.$isInstanceOf[Stuff[Proxy[PP]]]();
+    <synthetic> def canEqual(x$1: Any): Boolean = x$1.$isInstanceOf[Stuff[_ <: [PP]Proxy[PP]]]();
     override <synthetic> def hashCode(): Int = ScalaRunTime.this._hashCode(Stuff.this);
     override <synthetic> def toString(): String = ScalaRunTime.this._toString(Stuff.this);
     override <synthetic> def equals(x$1: Any): Boolean = x$1 match {
@@ -38,9 +38,3 @@
   }
 }
```

I also heeded my own advice to pass in a prefix to this method.

1 files changed, 2 insertions, 3 deletions

diff --git a/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala b/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala
index 99e61d2482..9b73f203e0 100644
--- a/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala
+++ b/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala
@@ -676,10 +676,9 @@ abstract class ClassfileParser {
               // so have to check unsafeTypeParams.isEmpty before worrying about raw type case below,
               // or we'll create a boatload of needless existentials.
               else if (classSym.isMonomorphicType || classSym.unsafeTypeParams.isEmpty) tp
-              else debuglogResult(s"raw type from $classSym"){
+              else debuglogResult(s"raw type from $classSym") {
                 // raw type - existentially quantify all type parameters
-                val eparams = typeParamsToExistentials(classSym, classSym.unsafeTypeParams)
-                newExistentialType(eparams, typeRef(pre, classSym, eparams.map(_.tpeHK)))
+                classExistentialType(pre, classSym)
               }
             case tp =>
               assert(sig.charAt(index) != '<', s"sig=$sig, index=$index, tp=$tp")