skip presuper vals in new encoding

Author: adriaanm

src/compiler/scala/tools/nsc/transform/Constructors.scala

@@ -591,7 +591,7 @@ abstract class Constructors extends Statics with Transform with ast.TreeDSL {
           case ValDef(mods, name, _, _) if mods hasFlag PRESUPER =>
             // stat is the constructor-local definition of the field value
             val fields = presupers filter (_.getterName == name)
-            assert(fields.length == 1)
+            assert(fields.length == 1, s"expected exactly one field by name $name in $presupers of $clazz's early initializers")
             val to = fields.head.symbol
 
             if (memoizeValue(to)) constrStatBuf += mkAssign(to, Ident(stat.symbol))

src/compiler/scala/tools/nsc/typechecker/MethodSynthesis.scala

@@ -486,7 +486,10 @@ trait MethodSynthesis {
       // as the symbol info is in the process of being created then.
       // TODO: harmonize tree & symbol creation
       // TODO: the `def field` call-site breaks when you add `|| vd.symbol.owner.isTrait` (detected in test suite)
-      def noFieldFor(vd: ValDef) = vd.mods.isDeferred || (vd.mods.isLazy && isUnitType(vd.symbol.info)) || owner.isTrait
+      def noFieldFor(vd: ValDef) = (
+        vd.mods.isDeferred
+      || (vd.mods.isLazy && isUnitType(vd.symbol.info))
+      || (owner.isTrait && !vd.mods.hasFlag(PRESUPER)))
     }
 
     case class Field(tree: ValDef) extends DerivedFromValDef {