SI-6566, unsoundness with alias variance.

This wasn't as bad as it could have been. All these changes
plug soundness holes in trunk. Mostly we're looking at type
aliases which were merely protected when they had to be
protected[this] not to allow unsound variance crossover.

14 files changed, 70 insertions, 14 deletions

diff --git a/src/library/scala/collection/TraversableLike.scala b/src/library/scala/collection/TraversableLike.scala
index a55257d128..fdbc5e9857 100644
--- a/src/library/scala/collection/TraversableLike.scala
+++ b/src/library/scala/collection/TraversableLike.scala
@@ -77,7 +77,7 @@ trait TraversableLike[+A, +Repr] extends Any
   import Traversable.breaks._
 
   /** The type implementing this traversable */
-  protected type Self = Repr
+  protected[this] type Self = Repr
 
   /** The collection of type $coll underlying this `TraversableLike` object.
    *  By default this is implemented as the `TraversableLike` object itself,
diff --git a/src/library/scala/collection/generic/GenericClassTagCompanion.scala b/src/library/scala/collection/generic/GenericClassTagCompanion.scala
index a587bbf544..76c12d118e 100644
--- a/src/library/scala/collection/generic/GenericClassTagCompanion.scala
+++ b/src/library/scala/collection/generic/GenericClassTagCompanion.scala
@@ -19,7 +19,7 @@ import scala.reflect.ClassTag
  *  @author Aleksandar Prokopec
  */
 abstract class GenericClassTagCompanion[+CC[X] <: Traversable[X]] {
-  type Coll = CC[_]
+  protected[this] type Coll = CC[_]
 
   def newBuilder[A](implicit ord: ClassTag[A]): Builder[A, CC[A]]
 
diff --git a/src/library/scala/collection/generic/GenericCompanion.scala b/src/library/scala/collection/generic/GenericCompanion.scala
index 5b03f8e5c6..b966ce51db 100644
--- a/src/library/scala/collection/generic/GenericCompanion.scala
+++ b/src/library/scala/collection/generic/GenericCompanion.scala
@@ -24,7 +24,7 @@ import scala.language.higherKinds
  */
 abstract class GenericCompanion[+CC[X] <: GenTraversable[X]] {
   /** The underlying collection type with unknown element type */
-  type Coll = CC[_]
+  protected[this] type Coll = CC[_]
 
   /** The default builder for `$Coll` objects.
    *  @tparam A      the type of the ${coll}'s elements
diff --git a/src/library/scala/collection/generic/GenericOrderedCompanion.scala b/src/library/scala/collection/generic/GenericOrderedCompanion.scala
index a9a50a1c35..094912c75a 100644
--- a/src/library/scala/collection/generic/GenericOrderedCompanion.scala
+++ b/src/library/scala/collection/generic/GenericOrderedCompanion.scala
@@ -19,7 +19,7 @@ import scala.language.higherKinds
  *  @since 2.8
  */
 abstract class GenericOrderedCompanion[+CC[X] <: Traversable[X]] {
-  type Coll = CC[_]
+  protected[this] type Coll = CC[_]
 
   def newBuilder[A](implicit ord: Ordering[A]): Builder[A, CC[A]]
 
diff --git a/src/library/scala/collection/immutable/TrieIterator.scala b/src/library/scala/collection/immutable/TrieIterator.scala
index f117bddb8c..550f4cd7e0 100644
--- a/src/library/scala/collection/immutable/TrieIterator.scala
+++ b/src/library/scala/collection/immutable/TrieIterator.scala
@@ -46,7 +46,7 @@ private[collection] abstract class TrieIterator[+T](elems: Array[Iterable[T]]) e
     case x: HashSetCollision1[_]    => x.ks.map(x => HashSet(x)).toArray
   }).asInstanceOf[Array[Iterable[T]]]
 
-  private type SplitIterators = ((Iterator[T], Int), Iterator[T])
+  private[this] type SplitIterators = ((Iterator[T], Int), Iterator[T])
 
   private def isTrie(x: AnyRef) = x match {
     case _: HashTrieMap[_,_] | _: HashTrieSet[_] => true
diff --git a/src/library/scala/collection/parallel/ParSeqLike.scala b/src/library/scala/collection/parallel/ParSeqLike.scala
index 201b624c72..874cf6fee9 100644
--- a/src/library/scala/collection/parallel/ParSeqLike.scala
+++ b/src/library/scala/collection/parallel/ParSeqLike.scala
@@ -44,8 +44,8 @@ trait ParSeqLike[+T, +Repr <: ParSeq[T], +Sequential <: Seq[T] with SeqLike[T, S
 extends scala.collection.GenSeqLike[T, Repr]
    with ParIterableLike[T, Repr, Sequential] {
 self =>
-  
-  type SuperParIterator = IterableSplitter[T]
+
+  protected[this] type SuperParIterator = IterableSplitter[T]
 
   /** A more refined version of the iterator found in the `ParallelIterable` trait,
    *  this iterator can be split into arbitrary subsets of iterators.
diff --git a/src/reflect/scala/reflect/internal/Symbols.scala b/src/reflect/scala/reflect/internal/Symbols.scala
index e14c617f24..0127bd988b 100644
--- a/src/reflect/scala/reflect/internal/Symbols.scala
+++ b/src/reflect/scala/reflect/internal/Symbols.scala
@@ -900,7 +900,7 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
     }
 
     /** The variance of this symbol. */
-    final def variance: Variance =
+    def variance: Variance =
       if (isCovariant) Covariant
       else if (isContravariant) Contravariant
       else Invariant
@@ -2635,6 +2635,9 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
   class AliasTypeSymbol protected[Symbols] (initOwner: Symbol, initPos: Position, initName: TypeName)
   extends TypeSymbol(initOwner, initPos, initName) {
     type TypeOfClonedSymbol = TypeSymbol
+    override def variance = if (hasLocalFlag) Bivariant else info.typeSymbol.variance
+    override def isContravariant = variance.isContravariant
+    override def isCovariant     = variance.isCovariant
     final override def isAliasType = true
     override def cloneSymbolImpl(owner: Symbol, newFlags: Long): TypeSymbol =
       owner.newNonClassSymbol(name, pos, newFlags)
diff --git a/src/reflect/scala/reflect/internal/Variances.scala b/src/reflect/scala/reflect/internal/Variances.scala
index df0a502b30..739dd69992 100644
--- a/src/reflect/scala/reflect/internal/Variances.scala
+++ b/src/reflect/scala/reflect/internal/Variances.scala
@@ -73,9 +73,8 @@ trait Variances {
         def nextVariance(sym: Symbol, v: Variance): Variance = (
           if (shouldFlip(sym, tvar)) v.flip
           else if (isLocalOnly(sym)) Bivariant
-          else if (!sym.isAliasType) v
-          else if (sym.isOverridingSymbol) Invariant
-          else Bivariant
+          else if (sym.isAliasType) Invariant
+          else v
         )
         def loop(sym: Symbol, v: Variance): Variance = (
           if (sym == tvar.owner || v.isBivariant) v
@@ -145,12 +144,12 @@ trait Variances {
         || sym.owner.isCaseApplyOrUnapply
       )
       tree match {
+        case defn: MemberDef if skip =>
+          log(s"Skipping variance check of ${sym.defString}")
         case ClassDef(_, _, _, _) | TypeDef(_, _, _, _) =>
           validateVariance(sym)
           super.traverse(tree)
         // ModuleDefs need not be considered because they have been eliminated already
-        case defn: ValOrDefDef if skip =>
-          log(s"Skipping variance check of $sym")
         case ValDef(_, _, _, _) =>
           validateVariance(sym)
         case DefDef(_, _, tparams, vparamss, _, _) =>
diff --git a/test/files/neg/t6566a.check b/test/files/neg/t6566a.check
new file mode 100644
index 0000000000..7668f9d2fb
--- /dev/null
+++ b/test/files/neg/t6566a.check
@@ -0,0 +1,4 @@
+t6566a.scala:2: error: covariant type T occurs in invariant position in type T of type MyType
+  class TypeCheat[+T] { type MyType = T }
+                             ^
+one error found
diff --git a/test/files/neg/t6566a.scala b/test/files/neg/t6566a.scala
new file mode 100644
index 0000000000..74a0b38e56
--- /dev/null
+++ b/test/files/neg/t6566a.scala
@@ -0,0 +1,17 @@
+object WhatsYourTypeIsMyType {
+  class TypeCheat[+T] { type MyType = T }
+
+  class Foo {
+    val tc = new TypeCheat[Foo]
+    var x: tc.MyType = _
+    def setX() = x = new Foo
+  }
+  class Bar extends Foo {
+    override val tc = new TypeCheat[Bar]
+    def unsound = this
+
+    setX()
+    println(x.unsound)
+  }
+  def main(args: Array[String]): Unit = new Bar
+}
diff --git a/test/files/neg/t6566b.check b/test/files/neg/t6566b.check
new file mode 100644
index 0000000000..fb3fe81fca
--- /dev/null
+++ b/test/files/neg/t6566b.check
@@ -0,0 +1,4 @@
+t6566b.scala:3: error: covariant type T occurs in invariant position in type T of type MyType
+    type MyType = T
+         ^
+one error found
diff --git a/test/files/neg/t6566b.scala b/test/files/neg/t6566b.scala
new file mode 100644
index 0000000000..18ddebf88b
--- /dev/null
+++ b/test/files/neg/t6566b.scala
@@ -0,0 +1,19 @@
+object WhatsYourTypeIsMyType {
+  trait WithMyType[+T] {
+    type MyType = T
+  }
+
+  class Foo extends WithMyType[Foo] {
+    var x: MyType = _
+    def setX() = x = new Foo
+  }
+
+  class Bar extends Foo with WithMyType[Bar] {
+    def unsound { println("iAmABar") }
+
+    setX()
+    println(x.unsound)
+  }
+
+  def main(args: Array[String]): Unit = new Bar
+}
diff --git a/test/files/neg/variances.check b/test/files/neg/variances.check
index 0643e533b7..7d965e94dc 100644
--- a/test/files/neg/variances.check
+++ b/test/files/neg/variances.check
@@ -13,7 +13,10 @@ variances.scala:21: error: covariant type A occurs in invariant position in supe
 variances.scala:74: error: covariant type A occurs in contravariant position in type => test.Covariant.T[A]{val m: A => A} of value x
     val x: T[A] {
         ^
+variances.scala:89: error: covariant type T occurs in invariant position in type T of type A
+    type A = T
+         ^
 variances.scala:90: error: covariant type T occurs in contravariant position in type => test.TestAlias.B[C.this.A] of method foo
     def foo: B[A]
         ^
-6 errors found
+7 errors found
diff --git a/test/files/pos/variances-local.scala b/test/files/pos/variances-local.scala
new file mode 100644
index 0000000000..35e395095c
--- /dev/null
+++ b/test/files/pos/variances-local.scala
@@ -0,0 +1,7 @@
+class Foo1[+T] {
+  private[this] type MyType = T
+}
+
+class Foo2[+T] {
+  protected[this] type MyType = T
+}