Relaxes a typer check which fails valid code wi...

Relaxes a typer check which fails valid code with NoCommonType. If the
instantiated types or type bounds do not conform, it tries normalizing
the type before throwing the exception. Closes #4553. I wrote this patch
with adriaan already, but bonus review by moors.

2 files changed, 25 insertions, 8 deletions

diff --git a/src/compiler/scala/reflect/internal/Types.scala b/src/compiler/scala/reflect/internal/Types.scala
index ed5dd1bc72..e8b9dc0865 100644
--- a/src/compiler/scala/reflect/internal/Types.scala
+++ b/src/compiler/scala/reflect/internal/Types.scala
@@ -5574,26 +5574,32 @@ A type's typeSymbol should never be inspected directly.
    *  Returns list of list of bounds infos, where corresponding type
    *  parameters are renamed to tparams.
    */
-  private def matchingBounds(tps: List[Type], tparams: List[Symbol]): List[List[Type]] =
-    tps map {
+  private def matchingBounds(tps: List[Type], tparams: List[Symbol]): List[List[Type]] = {
+    def getBounds(tp: Type): List[Type] = tp match {
       case PolyType(tparams1, _) if sameLength(tparams1, tparams) =>
         tparams1 map (tparam => tparam.info.substSym(tparams1, tparams))
-      case _ =>
-        throw new NoCommonType(tps)
+      case tp =>
+        if (tp ne tp.normalize) getBounds(tp.normalize)
+        else throw new NoCommonType(tps)
     }
+    tps map getBounds
+  }
 
   /** All types in list must be polytypes with type parameter lists of
    *  same length as tparams.
    *  Returns list of instance types, where corresponding type
    *  parameters are renamed to tparams.
    */
-  private def matchingInstTypes(tps: List[Type], tparams: List[Symbol]): List[Type] =
-    tps map {
+  private def matchingInstTypes(tps: List[Type], tparams: List[Symbol]): List[Type] = {
+    def transformResultType(tp: Type): Type = tp match {
       case PolyType(tparams1, restpe) if sameLength(tparams1, tparams) =>
         restpe.substSym(tparams1, tparams)
-      case _ =>
-        throw new NoCommonType(tps)
+      case tp =>
+        if (tp ne tp.normalize) transformResultType(tp.normalize)
+        else throw new NoCommonType(tps)
     }
+    tps map transformResultType
+  }
 
   /** All types in list must be method types with equal parameter types.
    *  Returns list of their result types.
diff --git a/test/files/pos/bug4553.scala b/test/files/pos/bug4553.scala
new file mode 100755
index 0000000000..4eefe57b2b
--- /dev/null
+++ b/test/files/pos/bug4553.scala
@@ -0,0 +1,11 @@
+trait VectorLike[+T, +V[A] <: Vector[A]] {
+  def +[S, VResult[S] >: V[S]](v: VResult[S])
+}
+
+trait Vector[+T] extends VectorLike[T, Vector]
+trait ImmutableVector[T] extends Vector[T] with VectorLike[T, ImmutableVector]
+trait MutableVector[T] extends Vector[T] with VectorLike[T, MutableVector]
+
+object Test {
+  def f = (null: MutableVector[Int]) + (null: ImmutableVector[Int])
+}