Fix #536 - only load member classes of classes that are currently compiled.

It seems wasteful to load the member classes even of classes that are not currently compiled.
It also makes us vulnerable to any misinterpretation of Java file formats. In th particular
case of #536, we parsed a class an anonymous Collection$1 which was referring to the type
parameter of its enclosing class, but was not diagnosed as an inner class of the enclosing class.

Author: odersky

src/dotty/tools/backend/jvm/DottyBackendInterface.scala

@@ -678,8 +678,24 @@ class DottyBackendInterface()(implicit ctx: Context) extends BackendInterface{
 
     // members
     def primaryConstructor: Symbol = toDenot(sym).primaryConstructor
-    def nestedClasses: List[Symbol] = memberClasses //exitingPhase(currentRun.lambdaliftPhase)(sym.memberClasses)
-    def memberClasses: List[Symbol] = toDenot(sym).info.memberClasses.map(_.symbol).toList
+
+    /** For currently compiled classes: All locally defined classes including local classes.
+     *  The empty list for classes that are not currently compiled.
+     */
+    def nestedClasses: List[Symbol] = localClasses(ctx.flattenPhase)
+
+    /** For currently compiled classes: All classes that are declared as members of this class
+     *  (but not inherited ones). The empty list for classes that are not currently compiled.
+     */
+    def memberClasses: List[Symbol] = localClasses(ctx.lambdaLiftPhase)
+
+    private def localClasses(phase: Phase) =
+      if (sym.isDefinedInCurrentRun)
+        ctx.atPhase(phase) { implicit ctx =>
+          toDenot(sym).info.decls.filter(_.isClass).toList
+        }
+      else Nil
+
     def annotations: List[Annotation] = Nil
     def companionModuleMembers: List[Symbol] =  {
       // phase travel to exitingPickler: this makes sure that memberClassesOf only sees member classes,

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

@@ -235,6 +235,7 @@ object Phases {
     private val extensionMethodsCache = new PhaseCache(classOf[ExtensionMethods])
     private val erasureCache = new PhaseCache(classOf[Erasure])
     private val patmatCache = new PhaseCache(classOf[PatternMatcher])
+    private val lambdaLiftCache = new PhaseCache(classOf[LambdaLift])
     private val flattenCache = new PhaseCache(classOf[Flatten])
     private val explicitOuterCache = new PhaseCache(classOf[ExplicitOuter])
     private val gettersCache = new PhaseCache(classOf[Getters])
@@ -245,6 +246,7 @@ object Phases {
     def extensionMethodsPhase = extensionMethodsCache.phase
     def erasurePhase = erasureCache.phase
     def patmatPhase = patmatCache.phase
+    def lambdaLiftPhase = lambdaLiftCache.phase
     def flattenPhase = flattenCache.phase
     def explicitOuterPhase = explicitOuterCache.phase
     def gettersPhase = gettersCache.phase

tests/pos/i536.scala

@@ -0,0 +1,3 @@
+object Max {
+  java.util.Collections.max(null)
+}