Disallow higher-kinded types that simulate general existential types

We cannot handle such types in general. So we now check that a hk application

   C[args]

where some of the arguments are wildcards does not have as a supertype
a hk application

   ([X] -> B)[args]

2 files changed, 265 insertions, 0 deletions

diff --git a/tests/pos-scala2/GenTraversableFactory.scala b/tests/pos-scala2/GenTraversableFactory.scala
new file mode 100644
index 000000000..2f93ab27b
--- /dev/null
+++ b/tests/pos-scala2/GenTraversableFactory.scala
@@ -0,0 +1,252 @@
+/*                     __                                               *\
+**     ________ ___   / /  ___     Scala API                            **
+**    / __/ __// _ | / /  / _ |    (c) 2006-2013, LAMP/EPFL             **
+**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
+** /____/\___/_/ |_/____/_/ | |                                         **
+**                          |/                                          **
+\*                                                                      */
+
+
+package scala
+package collection
+package generic
+
+import scala.language.higherKinds
+
+/** A template for companion objects of `Traversable` and subclasses thereof.
+ *  This class provides a set of operations to create `$Coll` objects.
+ *  It is typically inherited by companion objects of subclasses of `Traversable`.
+ *
+ *  @since 2.8
+ *
+ *  @define coll collection
+ *  @define Coll `Traversable`
+ *  @define factoryInfo
+ *    This object provides a set of operations to create `$Coll` values.
+ *    @author Martin Odersky
+ *    @version 2.8
+ *  @define canBuildFromInfo
+ *    The standard `CanBuildFrom` instance for $Coll objects.
+ *    @see CanBuildFrom
+ *  @define genericCanBuildFromInfo
+ *    The standard `CanBuildFrom` instance for $Coll objects.
+ *    The created value is an instance of class `GenericCanBuildFrom`,
+ *    which forwards calls to create a new builder to the
+ *    `genericBuilder` method of the requesting collection.
+ *    @see CanBuildFrom
+ *    @see GenericCanBuildFrom
+ */
+abstract class GenTraversableFactory[CC[X] <: GenTraversable[X] with GenericTraversableTemplate[X, CC]]
+extends GenericCompanion[CC] {
+
+  private[this] val ReusableCBFInstance: GenericCanBuildFrom[Nothing] = new GenericCanBuildFrom[Nothing] {
+    override def apply() = newBuilder[Nothing]
+  }
+  def ReusableCBF: GenericCanBuildFrom[Nothing] = ReusableCBFInstance
+
+  /** A generic implementation of the `CanBuildFrom` trait, which forwards
+   *  all calls to `apply(from)` to the `genericBuilder` method of
+   *  $coll `from`, and which forwards all calls of `apply()` to the
+   *  `newBuilder` method of this factory.
+   */
+  class GenericCanBuildFrom[A] extends CanBuildFrom[CC[_], A, CC[A]] {
+    /** Creates a new builder on request of a collection.
+     *  @param from  the collection requesting the builder to be created.
+     *  @return the result of invoking the `genericBuilder` method on `from`.
+     */
+    def apply(from: Coll) = from.genericBuilder[A]
+
+    /** Creates a new builder from scratch
+     *  @return the result of invoking the `newBuilder` method of this factory.
+     */
+    def apply() = newBuilder[A]
+  }
+
+  /** Concatenates all argument collections into a single $coll.
+   *
+   *  @param xss the collections that are to be concatenated.
+   *  @return the concatenation of all the collections.
+   */
+  def concat[A](xss: Traversable[A]*): CC[A] = {
+    val b = newBuilder[A]
+    // At present we're using IndexedSeq as a proxy for "has a cheap size method".
+    if (xss forall (_.isInstanceOf[IndexedSeq[_]]))
+      b.sizeHint(xss.map(_.size).sum)
+
+    for (xs <- xss.seq) b ++= xs
+    b.result()
+  }
+
+  /** Produces a $coll containing the results of some element computation a number of times.
+   *  @param   n  the number of elements contained in the $coll.
+   *  @param   elem the element computation
+   *  @return  A $coll that contains the results of `n` evaluations of `elem`.
+   */
+  def fill[A](n: Int)(elem: => A): CC[A] = {
+    val b = newBuilder[A]
+    b.sizeHint(n)
+    var i = 0
+    while (i < n) {
+      b += elem
+      i += 1
+    }
+    b.result()
+  }
+
+  /** Produces a two-dimensional $coll containing the results of some element computation a number of times.
+   *  @param   n1  the number of elements in the 1st dimension
+   *  @param   n2  the number of elements in the 2nd dimension
+   *  @param   elem the element computation
+   *  @return  A $coll that contains the results of `n1 x n2` evaluations of `elem`.
+   */
+  def fill[A](n1: Int, n2: Int)(elem: => A): CC[CC[A]] =
+    tabulate(n1)(_ => fill(n2)(elem))
+
+  /** Produces a three-dimensional $coll containing the results of some element computation a number of times.
+   *  @param   n1  the number of elements in the 1st dimension
+   *  @param   n2  the number of elements in the 2nd dimension
+   *  @param   n3  the number of elements in the 3nd dimension
+   *  @param   elem the element computation
+   *  @return  A $coll that contains the results of `n1 x n2 x n3` evaluations of `elem`.
+   */
+  def fill[A](n1: Int, n2: Int, n3: Int)(elem: => A): CC[CC[CC[A]]] =
+    tabulate(n1)(_ => fill(n2, n3)(elem))
+
+  /** Produces a four-dimensional $coll containing the results of some element computation a number of times.
+   *  @param   n1  the number of elements in the 1st dimension
+   *  @param   n2  the number of elements in the 2nd dimension
+   *  @param   n3  the number of elements in the 3nd dimension
+   *  @param   n4  the number of elements in the 4th dimension
+   *  @param   elem the element computation
+   *  @return  A $coll that contains the results of `n1 x n2 x n3 x n4` evaluations of `elem`.
+   */
+  def fill[A](n1: Int, n2: Int, n3: Int, n4: Int)(elem: => A): CC[CC[CC[CC[A]]]] =
+    tabulate(n1)(_ => fill(n2, n3, n4)(elem))
+
+  /** Produces a five-dimensional $coll containing the results of some element computation a number of times.
+   *  @param   n1  the number of elements in the 1st dimension
+   *  @param   n2  the number of elements in the 2nd dimension
+   *  @param   n3  the number of elements in the 3nd dimension
+   *  @param   n4  the number of elements in the 4th dimension
+   *  @param   n5  the number of elements in the 5th dimension
+   *  @param   elem the element computation
+   *  @return  A $coll that contains the results of `n1 x n2 x n3 x n4 x n5` evaluations of `elem`.
+   */
+  def fill[A](n1: Int, n2: Int, n3: Int, n4: Int, n5: Int)(elem: => A): CC[CC[CC[CC[CC[A]]]]] =
+    tabulate(n1)(_ => fill(n2, n3, n4, n5)(elem))
+
+  /** Produces a $coll containing values of a given function over a range of integer values starting from 0.
+   *  @param  n   The number of elements in the $coll
+   *  @param  f   The function computing element values
+   *  @return A $coll consisting of elements `f(0), ..., f(n -1)`
+   */
+  def tabulate[A](n: Int)(f: Int => A): CC[A] = {
+    val b = newBuilder[A]
+    b.sizeHint(n)
+    var i = 0
+    while (i < n) {
+      b += f(i)
+      i += 1
+    }
+    b.result()
+  }
+
+  /** Produces a two-dimensional $coll containing values of a given function over ranges of integer values starting from 0.
+   *  @param   n1  the number of elements in the 1st dimension
+   *  @param   n2  the number of elements in the 2nd dimension
+   *  @param   f   The function computing element values
+   *  @return A $coll consisting of elements `f(i1, i2)`
+   *          for `0 <= i1 < n1` and `0 <= i2 < n2`.
+   */
+  def tabulate[A](n1: Int, n2: Int)(f: (Int, Int) => A): CC[CC[A]] =
+    tabulate(n1)(i1 => tabulate(n2)(f(i1, _)))
+
+  /** Produces a three-dimensional $coll containing values of a given function over ranges of integer values starting from 0.
+   *  @param   n1  the number of elements in the 1st dimension
+   *  @param   n2  the number of elements in the 2nd dimension
+   *  @param   n3  the number of elements in the 3nd dimension
+   *  @param   f   The function computing element values
+   *  @return A $coll consisting of elements `f(i1, i2, i3)`
+   *          for `0 <= i1 < n1`, `0 <= i2 < n2`, and `0 <= i3 < n3`.
+   */
+  def tabulate[A](n1: Int, n2: Int, n3: Int)(f: (Int, Int, Int) => A): CC[CC[CC[A]]] =
+    tabulate(n1)(i1 => tabulate(n2, n3)(f(i1, _, _)))
+
+  /** Produces a four-dimensional $coll containing values of a given function over ranges of integer values starting from 0.
+   *  @param   n1  the number of elements in the 1st dimension
+   *  @param   n2  the number of elements in the 2nd dimension
+   *  @param   n3  the number of elements in the 3nd dimension
+   *  @param   n4  the number of elements in the 4th dimension
+   *  @param   f   The function computing element values
+   *  @return A $coll consisting of elements `f(i1, i2, i3, i4)`
+   *          for `0 <= i1 < n1`, `0 <= i2 < n2`, `0 <= i3 < n3`, and `0 <= i4 < n4`.
+   */
+  def tabulate[A](n1: Int, n2: Int, n3: Int, n4: Int)(f: (Int, Int, Int, Int) => A): CC[CC[CC[CC[A]]]] =
+    tabulate(n1)(i1 => tabulate(n2, n3, n4)(f(i1, _, _, _)))
+
+  /** Produces a five-dimensional $coll containing values of a given function over ranges of integer values starting from 0.
+   *  @param   n1  the number of elements in the 1st dimension
+   *  @param   n2  the number of elements in the 2nd dimension
+   *  @param   n3  the number of elements in the 3nd dimension
+   *  @param   n4  the number of elements in the 4th dimension
+   *  @param   n5  the number of elements in the 5th dimension
+   *  @param   f   The function computing element values
+   *  @return A $coll consisting of elements `f(i1, i2, i3, i4, i5)`
+   *          for `0 <= i1 < n1`, `0 <= i2 < n2`, `0 <= i3 < n3`, `0 <= i4 < n4`, and `0 <= i5 < n5`.
+   */
+  def tabulate[A](n1: Int, n2: Int, n3: Int, n4: Int, n5: Int)(f: (Int, Int, Int, Int, Int) => A): CC[CC[CC[CC[CC[A]]]]] =
+    tabulate(n1)(i1 => tabulate(n2, n3, n4, n5)(f(i1, _, _, _, _)))
+
+  /** Produces a $coll containing a sequence of increasing of integers.
+   *
+   *  @param start the first element of the $coll
+   *  @param end   the end value of the $coll (the first value NOT contained)
+   *  @return  a $coll with values `start, start + 1, ..., end - 1`
+   */
+  def range[T: Integral](start: T, end: T): CC[T] = range(start, end, implicitly[Integral[T]].one)
+
+  /** Produces a $coll containing equally spaced values in some integer interval.
+   *  @param start the start value of the $coll
+   *  @param end   the end value of the $coll (the first value NOT contained)
+   *  @param step  the difference between successive elements of the $coll (must be positive or negative)
+   *  @return      a $coll with values `start, start + step, ...` up to, but excluding `end`
+   */
+  def range[T: Integral](start: T, end: T, step: T): CC[T] = {
+    val num = implicitly[Integral[T]]
+    import num._
+
+    if (step == zero) throw new IllegalArgumentException("zero step")
+    val b = newBuilder[T]
+    b sizeHint immutable.NumericRange.count(start, end, step, isInclusive = false)
+    var i = start
+    while (if (/*num.mkOrderingOps*/(step) < zero) end < i else i < end) {
+      b += i
+      i += step
+    }
+    b.result()
+  }
+
+  /** Produces a $coll containing repeated applications of a function to a start value.
+   *
+   *  @param start the start value of the $coll
+   *  @param len   the number of elements contained inthe $coll
+   *  @param f     the function that's repeatedly applied
+   *  @return      a $coll with `len` values in the sequence `start, f(start), f(f(start)), ...`
+   */
+  def iterate[A](start: A, len: Int)(f: A => A): CC[A] = {
+    val b = newBuilder[A]
+    if (len > 0) {
+      b.sizeHint(len)
+      var acc = start
+      var i = 1
+      b += acc
+
+      while (i < len) {
+        acc = f(acc)
+        i += 1
+        b += acc
+      }
+    }
+    b.result()
+  }
+}
diff --git a/tests/pos-scala2/t6014.scala b/tests/pos-scala2/t6014.scala
new file mode 100644
index 000000000..02535f377
--- /dev/null
+++ b/tests/pos-scala2/t6014.scala
@@ -0,0 +1,13 @@
+object Test {
+  case class CC[T](key: T)
+  type Alias[T] = Seq[CC[T]]
+
+  def f(xs: Seq[CC[_]]) = xs map { case CC(x) => CC(x) }    // ok
+  def g(xs: Alias[_])   = xs map { case CC(x) => CC(x) }    // migration warning: unreducible application
+  // ./a.scala:11: error: missing parameter type for expanded function
+  // The argument types of an anonymous function must be fully known. (SLS 8.5)
+  // Expected type was: ?
+  //   def g(xs: Alias[_])   = xs map { case CC(x) => CC(x) }    // fails
+  //                                  ^
+  // one error found
+}