Also consider type aliases when checking for realizability

Fixes #50.

Author: odersky

src/dotty/tools/dotc/core/Types.scala

@@ -139,7 +139,7 @@ object Types {
           case _ => false
         }
         isConcrete(tp) &&
-        tp.abstractTypeMembers.forall { m =>
+        tp.nonClassTypeMembers.forall { m =>
           val bounds = m.info.bounds
           bounds.lo <:< bounds.hi
         } ||
@@ -592,6 +592,12 @@ object Types {
           (name, buf) => buf += member(name).asSingleDenotation)
     }
 
+    /** The set of abstract type members of this type. */
+    final def nonClassTypeMembers(implicit ctx: Context): Seq[SingleDenotation] = track("nonClassTypeMembers") {
+      memberDenots(nonClassTypeNameFilter,
+          (name, buf) => buf += member(name).asSingleDenotation)
+    }
+
     /** The set of type members of this type */
     final def typeMembers(implicit ctx: Context): Seq[SingleDenotation] = track("typeMembers") {
       memberDenots(typeNameFilter,
@@ -3367,6 +3373,15 @@ object Types {
       }
   }
 
+  /** A filter for names of abstract types of a given type */
+  object nonClassTypeNameFilter extends NameFilter {
+    def apply(pre: Type, name: Name)(implicit ctx: Context): Boolean =
+      name.isTypeName && {
+        val mbr = pre.member(name)
+        mbr.symbol.isType && !mbr.symbol.isClass
+      }
+  }
+
   /** A filter for names of deferred term definitions of a given type */
   object abstractTermNameFilter extends NameFilter {
     def apply(pre: Type, name: Name)(implicit ctx: Context): Boolean =

test/dotc/tests.scala

@@ -159,6 +159,7 @@ class tests extends CompilerTest {
   @Test def neg_i705 = compileFile(negDir, "i705-inner-value-class", xerrors = 7)
   @Test def neg_i866 = compileFile(negDir, "i866", xerrors = 2)
   @Test def neg_i974 = compileFile(negDir, "i974", xerrors = 2)
+  @Test def neg_i1050 = compileFile(negDir, "i1050", xerrors = 2)
   @Test def neg_moduleSubtyping = compileFile(negDir, "moduleSubtyping", xerrors = 4)
   @Test def neg_escapingRefs = compileFile(negDir, "escapingRefs", xerrors = 2)
   @Test def neg_instantiateAbstract = compileFile(negDir, "instantiateAbstract", xerrors = 8)

tests/neg/i1050.scala

@@ -0,0 +1,24 @@
+trait A { type L <: Nothing }
+trait B { type L >: Any}
+object Test {
+  lazy val x: A & B = ???
+  val y: x.L = 1
+  val z: String = y
+}
+object Test50 {
+  trait A {
+    type X = String
+  }
+  trait B {
+    type X = Int
+  }
+  lazy val o: A & B = ???
+
+  def xToString(x: o.X): String = x
+
+  def intToString(i: Int): String = xToString(i)
+
+  def main(args: Array[String]) = {
+    val s: String = intToString(1)
+  }
+}