allow value overrides in traits; check variance...

allow value overrides in traits; check variances in existential types
(see #528)

2 files changed, 8 insertions, 6 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
index fa37dd5786..a689aa6fd5 100644
--- a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
@@ -182,9 +182,9 @@ abstract class RefChecks extends InfoTransform {
           overrideError("cannot override a mutable variable")
         } else if (other.isStable && !member.isStable) { // (1.4)
           overrideError("needs to be an immutable value")
-        } else if (other.isStable && !other.isDeferred && other.owner.isTrait && (member hasFlag OVERRIDE)) {
-          overrideError("cannot override a value or variable definition in a trait " +
-                        "\n (this is an implementation restriction)")
+//        } else if (other.isStable && !other.isDeferred && other.owner.isTrait && (member hasFlag OVERRIDE)) {
+//          overrideError("cannot override a value or variable definition in a trait " +
+//                        "\n (this is an implementation restriction)")
         } else {
           if (other.isAliasType) {
             //if (!member.typeParams.isEmpty) // (1.5)  @MAT
@@ -405,8 +405,10 @@ abstract class RefChecks extends InfoTransform {
           case MethodType(formals, result) =>
             validateVariance(result, variance)
           case PolyType(tparams, result) =>
+            // type parameters will be validated separately, because they are defined explicitly.
             validateVariance(result, variance)
           case ExistentialType(tparams, result) =>
+            validateVariances(tparams map (_.info), variance)
             validateVariance(result, variance)
           case AnnotatedType(attribs, tp, selfsym) =>
             validateVariance(tp, variance)
diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 806698dd65..ac7a40ba4f 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -2252,9 +2252,9 @@ trait Typers { self: Analyzer =>
         } else {
           if (!lhs1.tpe.isError) {
             //println(lhs1+" = "+rhs)//DEBUG
-            error(tree.pos, "assignment to "+
-                  (if ((varsym ne null) && varsym.isValue) "immutable value"
-                   else "non variable"))
+            error(tree.pos,
+                  if ((varsym ne null) && varsym.isValue) "reassignment to val"
+                  else "assignment to non variable")
           }
           setError(tree)
         }