Resume suspensions also when reading from classfiles

Make treatment in Scala2Unpickler and Namer the same and factor
out common functionality.

Author: odersky

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

@@ -374,7 +374,7 @@ trait TypeOps { this: Context => // TODO: Make standalone object.
               if (argSym is BaseTypeArg)
                 forwardRef(argSym, from, to, cls, decls)
           pref.info match {
-            case info: TempClassInfo => info.suspensions = (() => forward()) :: info.suspensions // !!! dotty deviation `forward` alone does not eta expand
+            case info: TempClassInfo => info.addSuspension(forward)
             case _ => forward()
           }
         }

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

@@ -3049,12 +3049,20 @@ object Types {
   /** 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
+    private var suspensions: List[() => Unit] = Nil
+
+    def addSuspension(suspension: () => Unit): Unit = suspensions ::= suspension
+
+    /** Install classinfo with known parents in `denot` and resume all suspensions */
+    def finalize(denot: SymDenotation, parents: List[TypeRef])(implicit ctx: Context) = {
+      denot.info = derivedClassInfo(classParents = parents)
+      suspensions.foreach(_())
+    }
   }
 
   object ClassInfo {

src/dotty/tools/dotc/core/unpickleScala2/Scala2Unpickler.scala

@@ -106,7 +106,8 @@ object Scala2Unpickler {
         // `denot.sourceModule.exists` provision i859.scala crashes in the backend.
         denot.owner.thisType select denot.sourceModule
       else selfInfo
-    denot.info = new TempClassInfo(denot.owner.thisType, denot.classSymbol, decls, ost) // first rough info to avoid CyclicReferences
+    val tempInfo = new TempClassInfo(denot.owner.thisType, denot.classSymbol, decls, ost)
+    denot.info = tempInfo // first rough info to avoid CyclicReferences
     var parentRefs = ctx.normalizeToClassRefs(parents, cls, decls)
     if (parentRefs.isEmpty) parentRefs = defn.ObjectType :: Nil
     for (tparam <- tparams) {
@@ -132,8 +133,7 @@ object Scala2Unpickler {
       registerCompanionPair(scalacCompanion, denot.classSymbol)
     }
 
-    denot.info = ClassInfo( // final info, except possibly for typeparams ordering
-      denot.owner.thisType, denot.classSymbol, parentRefs, decls, ost)
+    tempInfo.finalize(denot, parentRefs) // install final info, except possibly for typeparams ordering
     denot.ensureTypeParamsInCorrectOrder()
   }
 }

src/dotty/tools/dotc/typer/Namer.scala

@@ -688,8 +688,8 @@ class Namer { typer: Typer =>
         else createSymbol(self)
 
       // pre-set info, so that parent types can refer to type params
-      val tempClassInfo = new TempClassInfo(cls.owner.thisType, cls, decls, selfInfo)
-      denot.info = tempClassInfo
+      val tempInfo = new TempClassInfo(cls.owner.thisType, cls, decls, selfInfo)
+      denot.info = tempInfo
 
       // Ensure constructor is completed so that any parameter accessors
       // which have type trees deriving from its parameters can be
@@ -705,8 +705,7 @@ class Namer { typer: Typer =>
       typr.println(s"completing $denot, parents = $parents, parentTypes = $parentTypes, parentRefs = $parentRefs")
 
       index(rest)(inClassContext(selfInfo))
-      denot.info = ClassInfo(cls.owner.thisType, cls, parentRefs, decls, selfInfo)
-      tempClassInfo.suspensions.foreach(_())
+      tempInfo.finalize(denot, parentRefs)
 
       Checking.checkWellFormed(cls)
       if (isDerivedValueClass(cls)) cls.setFlag(Final)