Fix erasure of raw arrays

Author: DarkDimius

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

@@ -321,6 +321,7 @@ class TypeErasure(isJava: Boolean, semiEraseVCs: Boolean, isConstructor: Boolean
       val sym = tp.symbol
       if (!sym.isClass) this(tp.info)
       else if (semiEraseVCs && isDerivedValueClass(sym)) eraseDerivedValueClassRef(tp)
+      else if (sym == defn.ArrayClass) apply(tp.appliedTo(TypeBounds.empty)) // i966 shows that we can hit a raw Array type.
       else eraseNormalClassRef(tp)
     case tp: RefinedType =>
       val parent = tp.parent

src/dotty/tools/dotc/transform/Erasure.scala

@@ -109,7 +109,7 @@ class Erasure extends Phase with DenotTransformer { thisTransformer =>
   }
 
   def assertErased(tp: Type, tree: tpd.Tree = tpd.EmptyTree)(implicit ctx: Context): Unit =
-    assert(isErasedType(tp), i"The type $tp - ${tp.toString} of class ${tp.getClass} of tree $tree : ${tree.tpe} / ${tree.getClass} is illegal after erasure, phase = ${ctx.phase}")
+    assert(isErasedType(tp), i"The type $tp - ${tp.toString} of class ${tp.getClass} of tree $tree : ${tree.tpe} / ${tree.getClass} is illegal after erasure, phase = ${ctx.phase.prev}")
 }
 
 object Erasure extends TypeTestsCasts{

tests/pos/i966.scala

@@ -0,0 +1,15 @@
+package scala
+package collection
+package immutable
+
+import HashMap.{ HashTrieMap, HashMapCollision1, HashMap1 }
+import HashSet.{ HashTrieSet, HashSetCollision1, HashSet1 }
+
+object i996{
+
+  private[this] def collisionToArray[T](x: Iterable[T]): Array[Iterable[T]] = (x match {
+    case x: HashMapCollision1[_, _] => x.kvs.map(x => HashMap(x)).toArray
+    case x: HashSetCollision1[_]    => x.ks.map(x => HashSet(x)).toArray
+  }).asInstanceOf[Array[Iterable[T]]]
+
+}