Still giddy with the thrill of fixing #266, I v...

Still giddy with the thrill of fixing #266, I vanquish another pattern
matcher bug from the dawn of time. If you've always wanted to write code
like this:

  class Bob[K[_]] {
    def foo(other: Any) = other match {
      case x: (Bob[X] forSome { type X[_] })  =>
    }
  }

Now is your chance. Closes #1427, review by moors. (Is there a better
way to "shake off" the pattern existential?)

1 files changed, 6 insertions, 2 deletions

diff --git a/src/compiler/scala/tools/nsc/matching/Matrix.scala b/src/compiler/scala/tools/nsc/matching/Matrix.scala
index 2c9d974d61..0bd9caf506 100644
--- a/src/compiler/scala/tools/nsc/matching/Matrix.scala
+++ b/src/compiler/scala/tools/nsc/matching/Matrix.scala
@@ -155,8 +155,12 @@ trait Matrix extends MatrixAdditions {
       // XXX how will valsym.tpe differ from sym.tpe ?
       def tpe = valsym.tpe
 
-      lazy val ident  = ID(lhs)
-      lazy val valDef = tracing("typedVal", typer typedValDef (VAL(lhs) === rhs) setPos lhs.pos)
+      // See #1427 for an example of a crash which occurs unless we retype:
+      // in that instance there is an existential in the pattern.
+      lazy val ident  = typer typed { ID(lhs) setType null }
+      lazy val valDef = typer typedValDef {
+        (VAL(lhs) withType ident.tpe) === rhs
+      }
 
       override def toString() = "%s: %s = %s".format(lhs, lhs.info, rhs)
     }