Fix problems arising when hierarchies of classes are under completion

Fix problems arising when hierarchies of classes are under completion at the same time.
In this case it can happen that we see a subclass (e.g. Arrays.scala) which depends
on a superclass (e.g. GenTraversableLike.scala) that itself does not have its parents
defined yet. Previously, several things went wrong here

 - One of the base classes would be marked as frozen, even though it dod not have all
   members entered yet. This led to an error in finger printing.
 - The baseclasses and super class bits of the subclass would be computed before the parents
   of the middle class were known. The baseclasses would then be chached, leading to
   false results for isDerivedFrom.

We need to refine the logic for computing base classes, super class bits, and fingerprints
to account for that issue.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/dotty/tools/dotc/core/Flags.scala b/src/dotty/tools/dotc/core/Flags.scala
index 1271d7f6a..c8a9dc13b 100644
--- a/src/dotty/tools/dotc/core/Flags.scala
+++ b/src/dotty/tools/dotc/core/Flags.scala
@@ -348,6 +348,9 @@ object Flags {
   /** A bridge method. Set by Erasure */
   final val Bridge = termFlag(34, "<bridge>")
 
+  /** All class attributes are fully defined */
+  final val FullyCompleted = typeFlag(34, "<fully-completed>")
+
   /** Symbol is a Java varargs bridge */ // (needed?)
   final val VBridge = termFlag(35, "<vbridge>") // TODO remove