Fix #1865: Compute outer path at right phase

When computing the outer path, we need to be careful to dealias before erasure,
even if the outer path is demanded during erasure. Otherwise we lose prefixes.

Author: odersky

compiler/src/dotty/tools/dotc/transform/ExplicitOuter.scala

@@ -276,7 +276,7 @@ object ExplicitOuter {
           if (tpe.prefix eq NoPrefix) cls.owner.enclosingClass.thisType
           else tpe.prefix
         case _ =>
-          outerPrefix(tpe.underlying)
+          outerPrefix(tpe.underlying(ctx.withPhaseNoLater(ctx.erasurePhase)))
       }
     case tpe: TypeProxy =>
       outerPrefix(tpe.underlying)
@@ -339,6 +339,7 @@ object ExplicitOuter {
         val cls = fun.symbol.owner.asClass
         def outerArg(receiver: Tree): Tree = receiver match {
           case New(_) | Super(_, _) =>
+            println(i"outerarg: ${receiver.tpe} --> ${outerPrefix(receiver.tpe)} at ${ctx.phase}")
             singleton(fixThis(outerPrefix(receiver.tpe)))
           case This(_) =>
             ref(outerParamAccessor(cls)) // will be rewired to outer argument of secondary constructor in phase Constructors

tests/pending/pos/i1865.scala

@@ -0,0 +1,24 @@
+class AbsCell {
+  type T = Node
+  class Node
+}
+
+object Test {
+  def test: Unit = {
+    val cell = new AbsCell
+    new cell.T
+  }
+}
+
+class AbsCell2 {
+  type T = Node
+  val value: T = value
+  def set(x: T): Unit = {}
+  class Node
+}
+object init {
+  def main = {
+    val cell = new AbsCell2 { val init = new Node }
+    cell set (new cell.T)
+  }
+}