Fix #1401: Make sure all refs are forwarded

Faced with recursive dependencies through self types, we might have
to apply `normalizeToClassRefs` to a class P with a parent that is not
yet initialized (witnessed by P's parents being Nil). In that case
we should still execute forwardRefs on P, but we have to
wait in a suspension until P is initialized.

This avoids the problem raised in #1401. I am still not quite sure
why forwardRefs is needed, but it seems that asSeenFrom alone is not
enough to track the dependencies in this case.

1 files changed, 12 insertions, 1 deletions

diff --git a/src/dotty/tools/dotc/core/Types.scala b/src/dotty/tools/dotc/core/Types.scala
index 11da27265..8019750bf 100644
--- a/src/dotty/tools/dotc/core/Types.scala
+++ b/src/dotty/tools/dotc/core/Types.scala
@@ -3043,9 +3043,20 @@ object Types {
     override def toString = s"ClassInfo($prefix, $cls)"
   }
 
-  final class CachedClassInfo(prefix: Type, cls: ClassSymbol, classParents: List[TypeRef], decls: Scope, selfInfo: DotClass)
+  class CachedClassInfo(prefix: Type, cls: ClassSymbol, classParents: List[TypeRef], decls: Scope, selfInfo: DotClass)
     extends ClassInfo(prefix, cls, classParents, decls, selfInfo)
 
+  /** A class for temporary class infos where `parents` are not yet known. */
+  final class TempClassInfo(prefix: Type, cls: ClassSymbol, decls: Scope, selfInfo: DotClass)
+  extends CachedClassInfo(prefix, cls, Nil, decls, selfInfo) {
+  
+    /** A list of actions that were because they rely on the class info of `cls` to
+     *  be no longer temporary. These actions will be performed once `cls` gets a real
+     *  ClassInfo.
+     */
+    var suspensions: List[() => Unit] = Nil
+  }
+
   object ClassInfo {
     def apply(prefix: Type, cls: ClassSymbol, classParents: List[TypeRef], decls: Scope, selfInfo: DotClass = NoType)(implicit ctx: Context) =
       unique(new CachedClassInfo(prefix, cls, classParents, decls, selfInfo))