Several fixes and refactorings for typechecking

1) Refactoring of package loaders that ensures that a package is always loaded before new members are entered. This led to a refactoring of sourceModule in completers into its own trait

2) Refactoring of optSelfType ot selfInfo. Class Infos may now have a reference to a symbol in their selfInfo field, instead of always a type, as it was before. This allows to introduce laziness for self type evaluation. Laziness is needed so that modules can be desugared and the desugared version be compiled without special tricks.

3) <init> and $init members are no longer inherited.

4) Refactoring of createSymbol and enterSym, so that creating symbols and entering them in a scope is decoupled.
    Renamed the driver operation form `enterSym(s)` to `index`.

1 files changed, 7 insertions, 3 deletions

diff --git a/src/dotty/tools/dotc/core/Denotations.scala b/src/dotty/tools/dotc/core/Denotations.scala
index bfd150999..272b6f505 100644
--- a/src/dotty/tools/dotc/core/Denotations.scala
+++ b/src/dotty/tools/dotc/core/Denotations.scala
@@ -333,11 +333,11 @@ object Denotations {
   /** An overloaded denotation consisting of the alternatives of both given denotations.
    */
   case class MultiDenotation(denot1: Denotation, denot2: Denotation) extends Denotation {
-    final def symbol = unsupported("symbol")
-    final def info = unsupported("info")
+    final def symbol = multiHasNot("symbol")
+    final def info = multiHasNot("info")
     final def validFor = denot1.validFor & denot2.validFor
     final def isType = false
-    def signature(implicit ctx: Context) = unsupported("signature")
+    def signature(implicit ctx: Context) = multiHasNot("signature")
     def atSignature(sig: Signature)(implicit ctx: Context): SingleDenotation =
       denot1.atSignature(sig) orElse denot2.atSignature(sig)
     def current(implicit ctx: Context): Denotation =
@@ -364,6 +364,10 @@ object Denotations {
     def derivedMultiDenotation(d1: Denotation, d2: Denotation) =
       if ((d1 eq denot1) && (d2 eq denot2)) this else MultiDenotation(d1, d2)
     override def toString = alternatives.mkString(" <and> ")
+
+    private def multiHasNot(op: String): Nothing =
+      throw new UnsupportedOperationException(
+        s"multi-denotation with alternatives $alternatives does not implement operation $op")
   }
 
   /** A non-overloaded denotation */