Invalidate companions of classes lifted by FlatMap

RestoreScopes enters classes lifted by FlatMap into the
enclosing package scope. It should also invalidate any companions
because otherwise we risk linking up a new class with a previously
generated companion which exists only as a Java classfile.

Author: odersky

src/dotty/tools/dotc/transform/RestoreScopes.scala

@@ -8,7 +8,10 @@ import Symbols._
 import Scopes._
 import collection.mutable
 import TreeTransforms.MiniPhaseTransform
+import SymDenotations._
 import ast.Trees._
+import NameOps._
+import typer.Mode
 import TreeTransforms.TransformerInfo
 
 /** The preceding lambda lift and flatten phases move symbols to different scopes
@@ -19,16 +22,32 @@ class RestoreScopes extends MiniPhaseTransform with IdentityDenotTransformer { t
   import ast.tpd._
   override def phaseName = "restoreScopes"
 
+  private def invalidateUndefinedCompanions(pkg: ClassSymbol, cls: ClassSymbol)(implicit ctx: Context): Unit = {
+    val otherNames = 
+      if (cls is Flags.Module) 
+        List(cls.name.sourceModuleName, cls.name.stripModuleClassSuffix.toTypeName)
+      else
+        List(cls.name.toTermName, cls.name.moduleClassName)
+    for (otherName <- otherNames) {
+      val other = pkg.info.decl(otherName).asSymDenotation
+      if (other.exists && !other.isCompleted) other.markAbsent
+    }    
+  }
+
   override def transformTypeDef(tree: TypeDef)(implicit ctx: Context, info: TransformerInfo) = {
     val TypeDef(_, impl: Template) = tree
+    // 
     val restoredDecls = newScope
     for (stat <- impl.constr :: impl.body)
       if (stat.isInstanceOf[MemberDef] && stat.symbol.exists)
         restoredDecls.enter(stat.symbol)
-    val cls = tree.symbol.asClass
-    cls.owner.asClass.enter(cls) 
       // Enter class in enclosing package scope, in case it was an inner class before flatten.
       // For top-level classes this does nothing.
+    val cls = tree.symbol.asClass
+    val pkg = cls.owner.asClass
+    pkg.enter(cls) 
+    invalidateUndefinedCompanions(pkg, cls)(
+        ctx.withPhase(cls.initial.validFor.phaseId).addMode(Mode.FutureDefsOK))
     val cinfo = cls.classInfo
     tree.symbol.copySymDenotation(
       info = cinfo.derivedClassInfo( // Dotty deviation: Cannot expand cinfo inline without a type error