Merge postConditions of memoize and constructors

If memoize and constructors are run in different groups,
memoize's previous postcondition "all concerete methods are implemented"
is wrong, because constructors are not implemengted yet. Solved
by moving the postcondition to phase Constructors.

Author: odersky

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

@@ -30,15 +30,19 @@ class Constructors extends MiniPhaseTransform with SymTransformer { thisTransfor
   import tpd._
 
   override def phaseName: String = "constructors"
-  override def runsAfter: Set[Class[_ <: Phase]] = Set(classOf[Erasure])
+  override def runsAfter: Set[Class[_ <: Phase]] = Set(classOf[Memoize])
 
 
-  /** All initializers should be moved into constructor
-    */
+  /** All initializers for non-lazy fields should be moved into constructor.
+   *  All non-abstract methods should be implemented (this is assured for constructors
+   *  in this phase and for other methods in memoize).
+   */
   override def checkPostCondition(tree: tpd.Tree)(implicit ctx: Context): Unit = {
     tree match {
-      case t: ValDef if ((t.rhs ne EmptyTree) && !(t.symbol is Flags.Lazy) && t.symbol.owner.isClass) =>
-        assert(false, i"$t initializers should be moved to constructors")
+      case tree: ValDef if tree.symbol.exists && tree.symbol.owner.isClass && !tree.symbol.is(Lazy) =>
+        assert(tree.rhs.isEmpty, i"$tree: initializer should be moved to constructors")
+      case tree: DefDef if !tree.symbol.is(LazyOrDeferred) =>
+        assert(!tree.rhs.isEmpty, i"unimplemented: $tree")
       case _ =>
     }
   }

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

@@ -42,12 +42,6 @@ import Decorators._
    */
   override def runsAfter: Set[Class[_ <: Phase]] = Set(classOf[Mixin])
 
-  override def checkPostCondition(tree: Tree)(implicit ctx: Context): Unit = tree match {
-    case tree: DefDef if !tree.symbol.is(Lazy | Deferred) =>
-      assert(!tree.rhs.isEmpty, i"unimplemented: $tree")
-    case _ =>
-  }
-
   override def transformDefDef(tree: DefDef)(implicit ctx: Context, info: TransformerInfo): Tree = {
     val sym = tree.symbol