New attempt to fix the leaking companion problem

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

@@ -5,6 +5,10 @@ import core._
 import DenotTransformers.SymTransformer
 import Phases.Phase
 import Contexts.Context
+import Symbols._
+import Names.Name
+import NameOps._
+import typer.Mode
 import Flags._
 import SymUtils._
 import SymDenotations.SymDenotation
@@ -16,11 +20,35 @@ class Flatten extends MiniPhaseTransform with SymTransformer { thisTransform =>
   import ast.tpd._
   override def phaseName = "flatten"
 
+  /** Mark absent any companion classes or objects of the flattened version of `cls`
+   *  in package `pkg` which are not yet completed. These are inner classes entered
+   *  into the package scope by reading their class files. They should never be read
+   *  because their information is superseded by the lifted class info.
+   */
+  private def invalidateUndefinedCompanions(pkg: ClassSymbol, cls: ClassSymbol)(implicit ctx: Context): Unit = {
+    def invalidate(otherName: Name) = {
+      val other = pkg.info.decl(otherName).asSymDenotation
+      if (other.exists && !other.isCompleted) other.markAbsent
+    }
+    if (cls is Flags.Module)  {
+      invalidate(cls.name.sourceModuleName)
+      invalidate(cls.name.stripModuleClassSuffix.toTypeName)
+    }
+    else {
+      invalidate(cls.name.toTermName)
+      invalidate(cls.name.moduleClassName)
+    }
+  }
+
   def transformSym(ref: SymDenotation)(implicit ctx: Context) = {
     if (ref.isClass && !ref.is(Package) && !ref.owner.is(Package)) {
+      val cls = ref.symbol.asClass
+      val pkg = ref.enclosingPackageClass.asClass
+      invalidateUndefinedCompanions(pkg, cls)(
+         ctx.withPhase(cls.initial.validFor.phaseId).addMode(Mode.FutureDefsOK))      
       ref.copySymDenotation(
         name = ref.flatName(),
-        owner = ref.enclosingPackageClass)
+        owner = pkg)
     }
     else ref
   }

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

@@ -6,12 +6,9 @@ import DenotTransformers.IdentityDenotTransformer
 import Contexts.Context
 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
@@ -22,18 +19,6 @@ 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
     // 
@@ -46,8 +31,6 @@ class RestoreScopes extends MiniPhaseTransform with IdentityDenotTransformer { t
     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