diff --git a/src/dotty/annotation/internal/Repeated.scala b/src/dotty/annotation/internal/Repeated.scala
new file mode 100644
index 000000000000..94e9df858d1f
--- /dev/null
+++ b/src/dotty/annotation/internal/Repeated.scala
@@ -0,0 +1,5 @@
+package dotty.annotation.internal
+
+import scala.annotation.Annotation
+
+final class Repeated() extends Annotation
\ No newline at end of file
diff --git a/src/dotty/tools/dotc/Compiler.scala b/src/dotty/tools/dotc/Compiler.scala
index 36af6a438035..a4a8fbbc84b1 100644
--- a/src/dotty/tools/dotc/Compiler.scala
+++ b/src/dotty/tools/dotc/Compiler.scala
@@ -21,7 +21,6 @@ class Compiler {
     List(
       List(new FrontEnd),
       List(new LazyValsCreateCompanionObjects,
-        /* new Constructors, */
            new TailRec),    //force separataion between lazyVals and LVCreateCO
       List(new PatternMatcher,
            new LazyValTranformContext().transformer,
@@ -30,7 +29,8 @@ class Compiler {
            new TypeTestsCasts,
            new InterceptedMethods),
       List(new Erasure),
-      List(new UncurryTreeTransform, new CollectEntryPoints)
+      List(new UncurryTreeTransform
+        /* , new Constructors */)
     )
 
   var runId = 1
diff --git a/src/dotty/tools/dotc/Main.scala b/src/dotty/tools/dotc/Main.scala
index 72f29fe6e9db..0b136d72f7b9 100644
--- a/src/dotty/tools/dotc/Main.scala
+++ b/src/dotty/tools/dotc/Main.scala
@@ -9,8 +9,6 @@ import core.Contexts.Context
 import reporting.Reporter
 
 /* To do:
-s *   - Revise the way classes are inherited - when not followed by [...] or (...),
- *     assume the unparameterized type and forward type parameters as we do now for the synthetic head class.
  */
 object Main extends Driver {
   def resident(compiler: Compiler): Reporter = unsupported("resident") /*loop { line =>
diff --git a/src/dotty/tools/dotc/Run.scala b/src/dotty/tools/dotc/Run.scala
index 247fa43365e1..a639b20cd770 100644
--- a/src/dotty/tools/dotc/Run.scala
+++ b/src/dotty/tools/dotc/Run.scala
@@ -42,8 +42,10 @@ class Run(comp: Compiler)(implicit ctx: Context) {
           phase.runOn(units)
           def foreachUnit(op: Context => Unit)(implicit ctx: Context): Unit =
             for (unit <- units) op(ctx.fresh.setPhase(phase.next).setCompilationUnit(unit))
-          if (ctx.settings.Xprint.value.containsPhase(phase)) foreachUnit(printTree)
-          if (ctx.settings.Ycheck.value.containsPhase(phase)) foreachUnit(TreeChecker.check)
+          if (ctx.settings.Xprint.value.containsPhase(phase))
+            foreachUnit(printTree)
+          if (ctx.settings.Ycheck.value.containsPhase(phase) && !ctx.reporter.hasErrors)
+            foreachUnit(TreeChecker.check)
         }
       }
     }
diff --git a/src/dotty/tools/dotc/ast/Desugar.scala b/src/dotty/tools/dotc/ast/Desugar.scala
index 8d891b9d96a8..513dee2ffe2a 100644
--- a/src/dotty/tools/dotc/ast/Desugar.scala
+++ b/src/dotty/tools/dotc/ast/Desugar.scala
@@ -751,7 +751,9 @@ object desugar {
           makeBinop(l, op, r)
       case PostfixOp(t, op) =>
         if ((ctx.mode is Mode.Type) && op == nme.raw.STAR)
-          AppliedTypeTree(ref(defn.RepeatedParamType), t)
+          Annotated(
+            New(ref(defn.RepeatedAnnot.typeRef), Nil :: Nil),
+            AppliedTypeTree(ref(defn.SeqClass.typeRef), t))
         else {
           assert(ctx.mode.isExpr, ctx.mode)
           Select(t, op)
diff --git a/src/dotty/tools/dotc/ast/Trees.scala b/src/dotty/tools/dotc/ast/Trees.scala
index 2ae494d558dc..e11bdeefc810 100644
--- a/src/dotty/tools/dotc/ast/Trees.scala
+++ b/src/dotty/tools/dotc/ast/Trees.scala
@@ -180,6 +180,8 @@ object Trees {
     def tokenPos: Seq[(Token, Position)] = ???
   }
 
+  private var nextId = 0
+
   /** Trees take a parameter indicating what the type of their `tpe` field
    *  is. Two choices: `Type` or `Untyped`.
    *  Untyped trees have type `Tree[Untyped]`.
@@ -204,6 +206,15 @@ object Trees {
 
     if (Stats.enabled) ntrees += 1
 
+    /** A unique identifier for this tree. Used for debugging, and potentially
+     *  tracking presentation compiler interactions
+     */
+    val uniqueId = {
+      nextId += 1
+      //assert(nextId != 214, this)
+      nextId
+    }
+
     /** The type  constructor at the root of the tree */
     type ThisTree[T >: Untyped] <: Tree[T]
 
diff --git a/src/dotty/tools/dotc/ast/tpd.scala b/src/dotty/tools/dotc/ast/tpd.scala
index e9775f1dc9c0..3b240ad2ca57 100644
--- a/src/dotty/tools/dotc/ast/tpd.scala
+++ b/src/dotty/tools/dotc/ast/tpd.scala
@@ -210,8 +210,24 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
   def TypeDef(sym: TypeSymbol)(implicit ctx: Context): TypeDef =
     ta.assignType(untpd.TypeDef(Modifiers(sym), sym.name, TypeTree(sym.info)), sym)
 
-  def ClassDef(cls: ClassSymbol, constr: DefDef, body: List[Tree])(implicit ctx: Context): TypeDef = {
-    val parents = cls.info.parents map (TypeTree(_))
+  def ClassDef(cls: ClassSymbol, constr: DefDef, body: List[Tree], superArgs: List[Tree] = Nil)(implicit ctx: Context): TypeDef = {
+    val firstParent :: otherParents = cls.info.parents
+    val superRef =
+      if (cls is Trait) TypeTree(firstParent)
+      else {
+        def isApplicable(ctpe: Type): Boolean = ctpe match {
+          case ctpe: PolyType =>
+            isApplicable(ctpe.instantiate(firstParent.argTypes))
+          case ctpe: MethodType =>
+            (superArgs corresponds ctpe.paramTypes)(_.tpe <:< _)
+          case _ =>
+            false
+        }
+        val constr = firstParent.decl(nme.CONSTRUCTOR).suchThat(constr => isApplicable(constr.info))
+        New(firstParent, constr.symbol.asTerm, superArgs)
+      }
+    val parents = superRef :: otherParents.map(TypeTree(_))
+
     val selfType =
       if (cls.classInfo.selfInfo ne NoType) ValDef(ctx.newSelfSym(cls))
       else EmptyValDef
@@ -260,10 +276,13 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
 
   // ------ Creating typed equivalents of trees that exist only in untyped form -------
 
-  /** new C(args) */
-  def New(tp: Type, args: List[Tree])(implicit ctx: Context): Apply = {
+  /** new C(args), calling the primary constructor of C */
+  def New(tp: Type, args: List[Tree])(implicit ctx: Context): Apply =
+    New(tp, tp.typeSymbol.primaryConstructor.asTerm, args)
+
+  /** new C(args), calling given constructor `constr` of C */
+  def New(tp: Type, constr: TermSymbol, args: List[Tree])(implicit ctx: Context): Apply = {
     val targs = tp.argTypes
-    val constr = tp.typeSymbol.primaryConstructor.asTerm
     Apply(
       Select(
         New(tp withoutArgs targs),
diff --git a/src/dotty/tools/dotc/config/Config.scala b/src/dotty/tools/dotc/config/Config.scala
index e77b10bfbaec..c247699da351 100644
--- a/src/dotty/tools/dotc/config/Config.scala
+++ b/src/dotty/tools/dotc/config/Config.scala
@@ -37,4 +37,10 @@ object Config {
 
   /** The recursion depth for showing a summarized string */
   final val summarizeDepth = 2
+
+  /** Track dependencies for constraint propagation satisfiability checking
+   *  If turned off, constraint checking is simpler but potentially slower
+   *  for large constraints.
+   */
+  final val trackConstrDeps = true
 }
\ No newline at end of file
diff --git a/src/dotty/tools/dotc/config/PathResolver.scala b/src/dotty/tools/dotc/config/PathResolver.scala
index 34678ae2bf54..f9f698e7238c 100644
--- a/src/dotty/tools/dotc/config/PathResolver.scala
+++ b/src/dotty/tools/dotc/config/PathResolver.scala
@@ -148,7 +148,7 @@ object PathResolver {
       println(Defaults)
     }
     else {
-      implicit val ctx = (new ContextBase).initialCtx
+      implicit val ctx: Context = (new ContextBase).initialCtx // Dotty deviation: implicits need explicit type
       val ArgsSummary(sstate, rest, errors) =
         ctx.settings.processArguments(args.toList, true)
       errors.foreach(println)
diff --git a/src/dotty/tools/dotc/core/Constraint.scala b/src/dotty/tools/dotc/core/Constraint.scala
index 64fb8764ebb6..339dbb64a343 100644
--- a/src/dotty/tools/dotc/core/Constraint.scala
+++ b/src/dotty/tools/dotc/core/Constraint.scala
@@ -10,6 +10,55 @@ import printing.Texts._
 import config.Config
 import config.Printers._
 
+object Constraint {
+
+  /** The type of `Constraint#myMap` */
+  type ParamInfo = SimpleMap[PolyType, Array[Type]]
+
+  /** The type of `Constraint#dependents */
+  type DependentMap = SimpleMap[PolyType, Array[Set[PolyParam]]]
+
+  /** The type of functions that include or exclude a `PolyParam` in or from a set*/
+  private type DepDelta = (Set[PolyParam], PolyParam) => Set[PolyParam]
+
+  private val addDep: DepDelta = (_ + _)
+  private val removeDep: DepDelta = (_ - _)
+
+  private val NoTypeBounds = new TypeBounds(WildcardType, WildcardType){}
+
+  /** An accumulator that changes dependencies on `param`.
+   *  @param  param       The parameter to which changed dependencies refer.
+   *  @param  ofVariance  Include `PolyParams` occurring at this variance in the dependencies.
+   *  @param  delta       The dependency change to perform (add or remove).
+   */
+  private class ChangeDependencies(param: PolyParam, ofVariance: Int, delta: DepDelta)(implicit ctx: Context)
+  extends TypeAccumulator[DependentMap] {
+    def apply(deps: DependentMap, tp: Type): DependentMap = tp match {
+      case tp @ PolyParam(pt, n) if
+        this.variance == 0 || this.variance == ofVariance =>
+        val oldDeps = deps(pt)
+        val original = safeSelect(oldDeps, n)
+        val changed = delta(original, param)
+        if (original eq changed) deps
+        else {
+          val newDeps =
+            if (oldDeps == null) new Array[Set[PolyParam]](pt.paramBounds.length)
+            else oldDeps.clone
+          newDeps(n) = changed
+          deps.updated(pt, newDeps)
+        }
+      case _ => foldOver(deps, tp)
+    }
+  }
+
+  /** `deps(n)`, except that `Set()` is returned if `deps` or `deps(n)` are null */
+  private def safeSelect(deps: Array[Set[PolyParam]], n: Int) : Set[PolyParam] =
+    if (deps == null || deps(n) == null) Set()
+    else deps(n)
+}
+
+import Constraint._
+
 /** Constraint over undetermined type parameters
  *  @param myMap a map from PolyType to arrays.
  *               Each array contains twice the number of entries as there a type parameters
@@ -18,8 +67,20 @@ import config.Printers._
  *               track the corresponding parameters, or is left empty (filled with nulls).
  *               An instantiated type parameter is represented by having its instance type in
  *               the corresponding array entry.
+ *  @param dependents a map from PolyTypes to arrays of Sets of PolyParams.
+ *               The i'th set in an array corresponding to polytype `pt` contains
+ *               those dependent `PolyParam`s `dp` that have `PolyParam(pt, i)` in their bounds in
+ *               significant position. A position is significant if solving the 
+ *               constraint for `(pt, i)` with a type higher than its lower bound
+ *               would lead to a constraint for `dp` that was not looser than
+ *               the existing constraint. Specifically, it means that all poly params
+ *               appearing covariantly in the lower bound and contravariantly in the
+ *               upper bound, as well as all poly params appearing nonvariantly are
+ *               significant.
+ *               The `dependents` map is maintained and queried only of `Config.trackConstrDeps` is set.
  */
-class Constraint(val myMap: SimpleMap[PolyType, Array[Type]]) extends Showable {
+class Constraint(private val myMap: ParamInfo,
+                 private val dependents: DependentMap) extends Showable {
 
   /** Does the constraint's domain contain the type parameters of `pt`? */
   def contains(pt: PolyType): Boolean = myMap(pt) != null
@@ -66,16 +127,88 @@ class Constraint(val myMap: SimpleMap[PolyType, Array[Type]]) extends Showable {
   def typeVarOfParam(param: PolyParam): Type = {
     val entries = myMap(param.binder)
     if (entries == null) NoType
-    else typeVar(entries, param.paramNum)
+    else {
+      val tvar = typeVar(entries, param.paramNum)
+      if (tvar != null) tvar else NoType
+    }
+  }
+
+  /** Change dependencies in map `deps` to reflect new parameter bounds.
+   *  @param deps       The map to change
+   *  @param pt         the polytype that contains the parameters which might have new bounds
+   *  @param entries    the entries for the parameters which might have new bounds
+   *  @param delta      the change operation, one of `addDep` or `removeDep`.
+   *  @param cmpEntries the comparison entries or `null` if no such entries exist.
+   *                    As an optimization, only bounds that differ between `entries`
+   *                    and `cmpEntries` will record their dependencies.
+   */
+  def changeDependencies(deps: DependentMap, pt: PolyType, entries: Array[Type], delta: DepDelta, cmpEntries: Array[Type])(implicit ctx: Context): DependentMap = {
+    val limit = paramCount(entries)
+    def loop(deps: DependentMap, n: Int): DependentMap = {
+      if (n >= limit) deps
+      else {
+        val newDeps = entries(n) match {
+          case bounds @ TypeBounds(lo, hi) =>
+            val cmpBounds =
+              if (cmpEntries == null) NoTypeBounds
+              else cmpEntries(n) match {
+                case bounds: TypeBounds => bounds
+                case _ => NoTypeBounds
+              }
+            if (cmpBounds eq bounds) deps
+            else {
+              val param = PolyParam(pt, n)
+              val deps1 =
+                if (cmpBounds.lo eq lo) deps
+                else new ChangeDependencies(param, 1, delta).apply(deps, lo)
+              val deps2 =
+                if (cmpBounds.hi eq hi) deps1
+                else new ChangeDependencies(param, -1, delta).apply(deps1, hi)
+              deps2
+            }
+          case _ =>
+            deps
+        }
+        loop(newDeps, n + 1)
+      }
+    }
+    if (Config.trackConstrDeps) loop(deps, 0) else deps
   }
 
+  /** Change dependencies to reflect all changes between the bounds in `oldMap` and `newMap`.
+   */
+  def diffDependencies(deps: DependentMap, oldMap: ParamInfo, newMap: ParamInfo)(implicit ctx: Context): DependentMap =
+    if (Config.trackConstrDeps) {
+      var d = deps
+      oldMap foreachBinding { (poly, entries) =>
+        val newEntries = newMap(poly)
+        if (newEntries ne entries) d = changeDependencies(d, poly, entries, removeDep, newEntries)
+      }
+      newMap foreachBinding { (poly, entries) =>
+        val oldEntries = oldMap(poly)
+        if (oldEntries ne entries) d = changeDependencies(d, poly, entries, addDep, oldEntries)
+      }
+      d
+    } else deps
+
+  /** The set of parameters that depend directly on `param`
+   *  according to what's stored in `dependents`.
+   */
+  def dependentParams(param: PolyParam): Set[PolyParam] =
+    safeSelect(dependents(param.binder), param.paramNum)
+
   /** A new constraint which is derived from this constraint by adding or replacing
    *  the entries corresponding to `pt` with `entries`.
    */
   private def updateEntries(pt: PolyType, entries: Array[Type])(implicit ctx: Context) : Constraint = {
-    val res = new Constraint(myMap.updated(pt, entries))
+    val res = new Constraint(
+      myMap.updated(pt, entries),
+      changeDependencies(dependents, pt, entries, addDep, myMap(pt)))
+      
+    //assert(res.domainPolys.filter(pt =>
+    //  pt.resultType.resultType.widen.classSymbol.name.toString == "Ensuring").length < 2) //DEBUG
     if (Config.checkConstraintsNonCyclic) checkNonCyclic(pt, entries)
-    ctx.runInfo.recordConstraintSize(res)
+    ctx.runInfo.recordConstraintSize(res, res.myMap.size)
     res
   }
 
@@ -114,7 +247,10 @@ class Constraint(val myMap: SimpleMap[PolyType, Array[Type]]) extends Showable {
     updateEntries(poly, myMap(poly) map op)
 
   /** A new constraint with all entries coming from `pt` removed. */
-  def remove(pt: PolyType) = new Constraint(myMap remove pt)
+  def remove(pt: PolyType)(implicit ctx: Context) =
+    new Constraint(
+      myMap remove pt,
+      changeDependencies(dependents, pt, myMap(pt), removeDep, null))
 
   /** Is entry associated with `pt` removable?
    *  @param removedParam The index of a parameter which is still present in the
@@ -185,7 +321,10 @@ class Constraint(val myMap: SimpleMap[PolyType, Array[Type]]) extends Showable {
 
     val pt = param.binder
     val constr1 = if (isRemovable(pt, param.paramNum)) remove(pt) else updated(param, tp)
-    val result = new Constraint(constr1.myMap mapValues subst)
+    val substMap = constr1.myMap mapValues subst
+    val result = new Constraint(
+      substMap,
+      diffDependencies(constr1.dependents, constr1.myMap, substMap))
     if (Config.checkConstraintsNonCyclic) result.checkNonCyclic()
     result
   }
@@ -243,6 +382,16 @@ class Constraint(val myMap: SimpleMap[PolyType, Array[Type]]) extends Showable {
       if isBounds(entries(n))
     } yield PolyParam(poly, n)
 
+  /** Check whether predicate holds for all parameters in constraint
+   */
+  def forallParams(p: PolyParam => Boolean): Boolean = {
+    myMap.foreachBinding { (poly, entries) =>
+      for (i <- 0 until paramCount(entries))
+        if (isBounds(entries(i)) && !p(PolyParam(poly, i))) return false
+    }
+    true
+  }
+
   /** Perform operation `op` on all typevars, or only on uninstantiated
    *  typevars, depending on whether `uninstOnly` is set or not.
    */
@@ -299,9 +448,9 @@ class Constraint(val myMap: SimpleMap[PolyType, Array[Type]]) extends Showable {
 trait ConstraintRunInfo { self: RunInfo =>
   private var maxSize = 0
   private var maxConstraint: Constraint = _
-  def recordConstraintSize(c: Constraint) =
-    if (c.myMap.size > maxSize) {
-      maxSize = c.myMap.size
+  def recordConstraintSize(c: Constraint, size: Int) =
+    if (size > maxSize) {
+      maxSize = size
       maxConstraint = c
     }
   def printMaxConstraint()(implicit ctx: Context) =
diff --git a/src/dotty/tools/dotc/core/Definitions.scala b/src/dotty/tools/dotc/core/Definitions.scala
index 9497438f2f33..6f34efc8bcc8 100644
--- a/src/dotty/tools/dotc/core/Definitions.scala
+++ b/src/dotty/tools/dotc/core/Definitions.scala
@@ -30,6 +30,9 @@ class Definitions {
   private def newCompleteClassSymbol(owner: Symbol, name: TypeName, flags: FlagSet, parents: List[TypeRef], decls: Scope = newScope) =
     ctx.newCompleteClassSymbol(owner, name, flags | Permanent, parents, decls).entered
 
+  private def newTopClassSymbol(name: TypeName, flags: FlagSet, parents: List[TypeRef]) =
+    completeClass(newCompleteClassSymbol(ScalaPackageClass, name, flags, parents))
+
   private def newTypeParam(cls: ClassSymbol, name: TypeName, flags: FlagSet, scope: MutableScope) =
     scope.enter(newSymbol(cls, name, flags | TypeParamCreationFlags, TypeBounds.empty))
 
@@ -74,7 +77,7 @@ class Definitions {
     newPolyMethod(cls, name, 1, resultTypeFn, flags)
 
   private def newT1EmptyParamsMethod(cls: ClassSymbol, name: TermName, resultTypeFn: PolyType => Type, flags: FlagSet) =
-    newPolyMethod(cls, name, 1, pt => MethodType(Nil, Nil, resultTypeFn(pt)), flags)
+    newPolyMethod(cls, name, 1, pt => MethodType(Nil, resultTypeFn(pt)), flags)
 
   private def mkArityArray(name: String, arity: Int, countFrom: Int): Array[ClassSymbol] = {
     val arr = new Array[ClassSymbol](arity + 1)
@@ -82,6 +85,12 @@ class Definitions {
     arr
   }
 
+  private def completeClass(cls: ClassSymbol): ClassSymbol = {
+    ensureConstructor(cls, EmptyScope)
+    if (cls.linkedClass.exists) cls.linkedClass.info = NoType
+    cls
+  }
+
   lazy val RootClass: ClassSymbol = ctx.newPackageSymbol(
     NoSymbol, nme.ROOT, (root, rootcls) => ctx.rootLoader(root)).moduleClass.asClass
   lazy val RootPackage: TermSymbol = ctx.newSymbol(
@@ -95,58 +104,67 @@ class Definitions {
   lazy val JavaPackageVal = ctx.requiredPackage("java")
   lazy val JavaLangPackageVal = ctx.requiredPackage("java.lang")
 
-  lazy val ObjectClass = ctx.requiredClass("java.lang.Object")
-  lazy val AnyRefAlias: TypeSymbol = newAliasType(tpnme.AnyRef, ObjectType)
-
-    lazy val Object_## = newMethod(ObjectClass, nme.HASHHASH, ExprType(IntType), Final)
-    lazy val Object_== = newMethod(ObjectClass, nme.EQ, methOfAny(BooleanType), Final)
-    lazy val Object_!= = newMethod(ObjectClass, nme.NE, methOfAny(BooleanType), Final)
-    lazy val Object_eq = newMethod(ObjectClass, nme.eq, methOfAnyRef(BooleanType), Final)
-    lazy val Object_ne = newMethod(ObjectClass, nme.ne, methOfAnyRef(BooleanType), Final)
-    lazy val Object_isInstanceOf = newT1ParameterlessMethod(ObjectClass, nme.isInstanceOf_Ob, _ => BooleanType, Final | Synthetic)
-    lazy val Object_asInstanceOf = newT1ParameterlessMethod(ObjectClass, nme.asInstanceOf_Ob, PolyParam(_, 0), Final | Synthetic)
-    lazy val Object_synchronized = newPolyMethod(ObjectClass, nme.synchronized_, 1,
-        pt => MethodType(List(PolyParam(pt, 0)), PolyParam(pt, 0)), Final)
-
-    def Object_getClass  = objMethod(nme.getClass_)
-    def Object_clone     = objMethod(nme.clone_)
-    def Object_finalize  = objMethod(nme.finalize_)
-    def Object_notify    = objMethod(nme.notify_)
-    def Object_notifyAll = objMethod(nme.notifyAll_)
-    def Object_equals    = objMethod(nme.equals_)
-    def Object_hashCode  = objMethod(nme.hashCode_)
-    def Object_toString  = objMethod(nme.toString_)
-    private def objMethod(name: PreName) = ObjectClass.requiredMethod(name)
-
-  lazy val AnyClass: ClassSymbol = {
-    val cls = newCompleteClassSymbol(ScalaPackageClass, tpnme.Any, Abstract, Nil)
-    ensureConstructor(cls, EmptyScope)
-    cls
-  }
-
-  lazy val AnyValClass: ClassSymbol = ctx.requiredClass("scala.AnyVal")
+  /** Note: We cannot have same named methods defined in Object and Any (and AnyVal, for that matter)
+   *  because after erasure the Any and AnyVal references get remapped to the Object methods
+   *  which would result in a double binding assertion failure.
+   * Instead we do the following:
+   *
+   *  - Have some methods exist only in Any, and remap them with the Erasure denotation
+   *    transformer to be owned by Object.
+   *  - Have other methods exist only in Object.
+   * To achieve this, we synthesize all Any and Object methods; Object methods no longer get
+   * loaded from a classfile.
+   *
+   * There's a remaining question about `getClass`. In Scala2.x `getClass` was handled by compiler magic.
+   * This is deemed too cumersome for Dotty and therefore right now `getClass` gets no special treatment;
+   * it's just a method on `Any` which returns the raw type `java.lang.Class`. An alternative
+   * way to get better `getClass` typing would be to treat `getClass` as a method of a generic
+   * decorator which gets remapped in a later phase to Object#getClass. Then we could give it
+   * the right type without changing the typechecker:
+   *
+   *     implicit class AnyGetClass[T](val x: T) extends AnyVal {
+   *       def getClass: java.lang.Class[T] = ???
+   *     }
+   */
+  lazy val AnyClass: ClassSymbol = completeClass(newCompleteClassSymbol(ScalaPackageClass, tpnme.Any, Abstract, Nil))
+  lazy val AnyValClass: ClassSymbol = completeClass(newCompleteClassSymbol(ScalaPackageClass, tpnme.AnyVal, Abstract, List(AnyClass.typeRef)))
 
-    lazy val AnyVal_getClass     = AnyValClass.requiredMethod(nme.getClass_)
     lazy val Any_==       = newMethod(AnyClass, nme.EQ, methOfAny(BooleanType), Final)
     lazy val Any_!=       = newMethod(AnyClass, nme.NE, methOfAny(BooleanType), Final)
     lazy val Any_equals   = newMethod(AnyClass, nme.equals_, methOfAny(BooleanType))
-    lazy val Any_hashCode = newMethod(AnyClass, nme.hashCode_, ExprType(IntType))
-    lazy val Any_toString = newMethod(AnyClass, nme.toString_, ExprType(StringType))
+    lazy val Any_hashCode = newMethod(AnyClass, nme.hashCode_, MethodType(Nil, IntType))
+    lazy val Any_toString = newMethod(AnyClass, nme.toString_, MethodType(Nil, StringType))
     lazy val Any_##       = newMethod(AnyClass, nme.HASHHASH, ExprType(IntType), Final)
-
-    // Any_getClass requires special handling.  The return type is determined on
-    // a per-call-site basis as if the function being called were actually:
-    //
-    //    // Assuming `target.getClass()`
-    //    def getClass[T](target: T): Class[_ <: T]
-    //
-    // Since getClass is not actually a polymorphic method, this requires compiler
-    // participation.  At the "Any" level, the return type is Class[_] as it is in
-    // java.lang.Object.  Java also special cases the return type.
-    lazy val Any_getClass     = newMethod(AnyClass, nme.getClass_, ExprType(Object_getClass.info.resultType), Deferred)
+    lazy val Any_getClass = newMethod(AnyClass, nme.getClass_, MethodType(Nil, ClassClass.typeRef), Final)
     lazy val Any_isInstanceOf = newT1ParameterlessMethod(AnyClass, nme.isInstanceOf_, _ => BooleanType, Final)
     lazy val Any_asInstanceOf = newT1ParameterlessMethod(AnyClass, nme.asInstanceOf_, PolyParam(_, 0), Final)
 
+    def AnyMethods = List(Any_==, Any_!=, Any_equals, Any_hashCode,
+      Any_toString, Any_##, Any_getClass, Any_isInstanceOf, Any_asInstanceOf)
+
+  lazy val ObjectClass: ClassSymbol = {
+    val cls = ctx.requiredClass("java.lang.Object")
+    assert(!cls.isCompleted, "race for completing java.lang.Object")
+    cls.info = ClassInfo(cls.owner.thisType, cls, AnyClass.typeRef :: Nil, newScope)
+    completeClass(cls)
+  }
+  lazy val AnyRefAlias: TypeSymbol = newAliasType(tpnme.AnyRef, ObjectType)
+
+    lazy val Object_eq = newMethod(ObjectClass, nme.eq, methOfAnyRef(BooleanType), Final)
+    lazy val Object_ne = newMethod(ObjectClass, nme.ne, methOfAnyRef(BooleanType), Final)
+    lazy val Object_synchronized = newPolyMethod(ObjectClass, nme.synchronized_, 1,
+        pt => MethodType(List(PolyParam(pt, 0)), PolyParam(pt, 0)), Final)
+    lazy val Object_clone = newMethod(ObjectClass, nme.clone_, MethodType(Nil, ObjectType), Protected)
+    lazy val Object_finalize = newMethod(ObjectClass, nme.finalize_, MethodType(Nil, UnitType), Protected)
+    lazy val Object_notify = newMethod(ObjectClass, nme.notify_, MethodType(Nil, UnitType))
+    lazy val Object_notifyAll = newMethod(ObjectClass, nme.notifyAll_, MethodType(Nil, UnitType))
+    lazy val Object_wait = newMethod(ObjectClass, nme.wait_, MethodType(Nil, UnitType))
+    lazy val Object_waitL = newMethod(ObjectClass, nme.wait_, MethodType(LongType :: Nil, UnitType))
+    lazy val Object_waitLI = newMethod(ObjectClass, nme.wait_, MethodType(LongType :: IntType :: Nil, UnitType))
+
+    def ObjectMethods = List(Object_eq, Object_ne, Object_synchronized, Object_clone,
+        Object_finalize, Object_notify, Object_notifyAll, Object_wait, Object_waitL, Object_waitLI)
+
   lazy val NotNullClass = ctx.requiredClass("scala.NotNull")
 
   lazy val NothingClass: ClassSymbol = newCompleteClassSymbol(
@@ -160,6 +178,7 @@ class Definitions {
   lazy val BoxesRunTimeClass      = BoxesRunTimeModule.moduleClass
   lazy val DottyPredefModule = ctx.requiredModule("dotty.DottyPredef")
   lazy val NilModule = ctx.requiredModule("scala.collection.immutable.Nil")
+  lazy val PredefConformsClass = ctx.requiredClass("scala.Predef." + tpnme.Conforms)
 
 //  lazy val FunctionClass: ClassSymbol = ctx.requiredClass("scala.Function")
   lazy val SingletonClass: ClassSymbol =
@@ -265,6 +284,7 @@ class Definitions {
   // Annotation classes
   lazy val AliasAnnot = ctx.requiredClass("dotty.annotation.internal.Alias")
   lazy val ChildAnnot = ctx.requiredClass("dotty.annotation.internal.Child")
+  lazy val RepeatedAnnot = ctx.requiredClass("dotty.annotation.internal.Repeated")
   lazy val InvariantBetweenClass = ctx.requiredClass("dotty.annotation.internal.InvariantBetween")
   lazy val CovariantBetweenClass = ctx.requiredClass("dotty.annotation.internal.CovariantBetween")
   lazy val ContravariantBetweenClass = ctx.requiredClass("dotty.annotation.internal.ContravariantBetween")
@@ -380,8 +400,8 @@ class Definitions {
 
   lazy val PhantomClasses = Set[Symbol](AnyClass, AnyValClass, NullClass, NothingClass)
 
-  lazy val asInstanceOfMethods = Set[Symbol](Any_asInstanceOf, Object_asInstanceOf)
-  lazy val isInstanceOfMethods = Set[Symbol](Any_isInstanceOf, Object_isInstanceOf)
+  lazy val asInstanceOfMethods = Set[Symbol](Any_asInstanceOf)
+  lazy val isInstanceOfMethods = Set[Symbol](Any_isInstanceOf)
   lazy val typeTestsOrCasts    = asInstanceOfMethods ++ isInstanceOfMethods
 
   lazy val RootImports = List[Symbol](JavaLangPackageVal, ScalaPackageVal, ScalaPredefModule, DottyPredefModule)
@@ -518,11 +538,11 @@ class Definitions {
 
   /** Lists core classes that don't have underlying bytecode, but are synthesized on-the-fly in every reflection universe */
   lazy val syntheticCoreClasses = List(
+    AnyClass,
     AnyRefAlias,
     RepeatedParamClass,
     JavaRepeatedParamClass,
     ByNameParamClass2x,
-    AnyClass,
     AnyValClass,
     NullClass,
     NothingClass,
@@ -531,26 +551,7 @@ class Definitions {
     EmptyPackageVal)
 
     /** Lists core methods that don't have underlying bytecode, but are synthesized on-the-fly in every reflection universe */
-    lazy val syntheticCoreMethods = List(
-      Any_==,
-      Any_!=,
-      Any_equals,
-      Any_hashCode,
-      Any_toString,
-      Any_getClass,
-      Any_isInstanceOf,
-      Any_asInstanceOf,
-      Any_##,
-      Object_eq,
-      Object_ne,
-      Object_==,
-      Object_!=,
-      Object_##,
-      Object_synchronized,
-      Object_isInstanceOf,
-      Object_asInstanceOf,
-      String_+
-    )
+    lazy val syntheticCoreMethods = AnyMethods ++ ObjectMethods ++ List(String_+)
 
   private[this] var _isInitialized = false
   def isInitialized = _isInitialized
diff --git a/src/dotty/tools/dotc/core/Denotations.scala b/src/dotty/tools/dotc/core/Denotations.scala
index e5f5e6f87529..9eab2bd040f7 100644
--- a/src/dotty/tools/dotc/core/Denotations.scala
+++ b/src/dotty/tools/dotc/core/Denotations.scala
@@ -600,7 +600,7 @@ object Denotations {
         case denot: SymDenotation => s"in ${denot.owner}"
         case _ => ""
       }
-      def msg = s"stale symbol; $this#${symbol.id} $ownerMsg, defined in run ${myValidFor.runId}, is referred to in run ${ctx.runId}"
+      def msg = s"stale symbol; $this#${symbol.id} $ownerMsg, defined in ${myValidFor}, is referred to in run ${ctx.period}"
       throw new StaleSymbol(msg)
     }
 
diff --git a/src/dotty/tools/dotc/core/Phases.scala b/src/dotty/tools/dotc/core/Phases.scala
index f76b83db69cd..251cd3876113 100644
--- a/src/dotty/tools/dotc/core/Phases.scala
+++ b/src/dotty/tools/dotc/core/Phases.scala
@@ -36,6 +36,8 @@ trait Phases {
 
   def atPhaseNotLaterThanTyper[T](op: Context => T): T =
     atPhaseNotLaterThan(base.typerPhase)(op)
+
+  def isAfterTyper: Boolean = base.isAfterTyper(phase)
 }
 
 object Phases {
@@ -177,9 +179,11 @@ object Phases {
     def refchecksPhase = refChecksCache.phase
     def erasurePhase = erasureCache.phase
     def flattenPhase = flattenCache.phase
+
+    def isAfterTyper(phase: Phase): Boolean = phase.id > typerPhase.id
   }
 
-  final val typerName = "typer"
+  final val typerName = "frontend"
   final val refChecksName = "refchecks"
   final val erasureName = "erasure"
   final val flattenName = "flatten"
diff --git a/src/dotty/tools/dotc/core/StdNames.scala b/src/dotty/tools/dotc/core/StdNames.scala
index cb4272f7a267..593feb9092e5 100644
--- a/src/dotty/tools/dotc/core/StdNames.scala
+++ b/src/dotty/tools/dotc/core/StdNames.scala
@@ -331,7 +331,6 @@ object StdNames {
     val asType: N               = "asType"
     val asClass: N              = "asClass"
     val asInstanceOf_ : N       = "asInstanceOf"
-    val asInstanceOf_Ob : N     = "$asInstanceOf"
     val assert_ : N             = "assert"
     val assume_ : N             = "assume"
     val box: N                  = "box"
@@ -388,7 +387,6 @@ object StdNames {
     val isDefinedAt: N          = "isDefinedAt"
     val isEmpty: N              = "isEmpty"
     val isInstanceOf_ : N       = "isInstanceOf"
-    val isInstanceOf_Ob : N     = "$isInstanceOf"
     val java: N                 = "java"
     val keepUnions: N           = "keepUnions"
     val key: N                  = "key"
diff --git a/src/dotty/tools/dotc/core/SymDenotations.scala b/src/dotty/tools/dotc/core/SymDenotations.scala
index 9cf06ec47f4e..c7e7dc50d13a 100644
--- a/src/dotty/tools/dotc/core/SymDenotations.scala
+++ b/src/dotty/tools/dotc/core/SymDenotations.scala
@@ -46,8 +46,9 @@ trait SymDenotations { this: Context =>
         case ClassInfo(_, _, _, _, selfInfo) => selfInfo == denot.symbol
         case _ => false
       }
-      stillValid(owner) && owner.isClass && (
-           (owner.decls.lookupAll(denot.name) contains denot.symbol)
+      stillValid(owner) && (
+           !owner.isClass
+        || (owner.decls.lookupAll(denot.name) contains denot.symbol)
         || isSelfSym
         )
     } catch {
diff --git a/src/dotty/tools/dotc/core/TypeApplications.scala b/src/dotty/tools/dotc/core/TypeApplications.scala
index 4b251f1839e2..c4845a249de4 100644
--- a/src/dotty/tools/dotc/core/TypeApplications.scala
+++ b/src/dotty/tools/dotc/core/TypeApplications.scala
@@ -111,7 +111,7 @@ class TypeApplications(val self: Type) extends AnyVal {
   /** Encode the type resulting from applying this type to given arguments */
   final def appliedTo(args: List[Type])(implicit ctx: Context): Type = /*>|>*/ track("appliedTo") /*<|<*/ {
 
-    def recur(tp: Type, tparams: List[TypeSymbol], args: List[Type]): Type = args match {
+    def matchParams(tp: Type, tparams: List[TypeSymbol], args: List[Type]): Type = args match {
       case arg :: args1 =>
         if (tparams.isEmpty) {
           println(s"applied type mismatch: $self $args, typeParams = $typeParams, tsym = ${self.typeSymbol.debugString}") // !!! DEBUG
@@ -119,32 +119,46 @@ class TypeApplications(val self: Type) extends AnyVal {
         }
         val tparam = tparams.head
         val tp1 = RefinedType(tp, tparam.name, arg.toBounds(tparam))
-        recur(tp1, tparams.tail, args1)
+        matchParams(tp1, tparams.tail, args1)
       case nil => tp
     }
 
-    def safeTypeParams(tsym: Symbol) =
-      if (tsym.isClass || !self.typeSymbol.isCompleting) typeParams
-      else {
-        ctx.warning("encountered F-bounded higher-kinded type parameters; assuming they are invariant")
-        defn.hkTrait(args map alwaysZero).typeParams
-      }
-
-    if (args.isEmpty || !canHaveTypeParams) self
-    else self match {
+    /** Instantiate type `tp` with `args`.
+     *  @param original  The original type for which we compute the type parameters
+     *                   This makes a difference for refinement types, because
+     *                   refinements bind type parameters and thereby remove them
+     *                   from `typeParams`.
+     */
+    def instantiate(tp: Type, original: Type): Type = tp match {
       case tp: TypeRef =>
         val tsym = tp.symbol
         if (tsym.isAliasType) tp.underlying.appliedTo(args)
-        else recur(tp, safeTypeParams(tsym), args)
+        else {
+          val safeTypeParams =
+            if (tsym.isClass || !tp.typeSymbol.isCompleting) original.typeParams
+            else {
+              ctx.warning("encountered F-bounded higher-kinded type parameters; assuming they are invariant")
+              defn.hkTrait(args map alwaysZero).typeParams
+            }
+          matchParams(tp, safeTypeParams, args)
+        }
+      case tp: RefinedType =>
+        tp.derivedRefinedType(
+          instantiate(tp.parent, original),
+          tp.refinedName,
+          tp.refinedInfo)
       case tp: TypeProxy =>
-        tp.underlying.appliedTo(args)
+        instantiate(tp.underlying, original)
       case AndType(l, r) =>
         l.appliedTo(args) & r
       case tp: PolyType =>
         tp.instantiate(args)
       case ErrorType =>
-        self
+        tp
     }
+
+    if (args.isEmpty || !canHaveTypeParams) self
+    else instantiate(self, self)
   }
 
   final def appliedTo(arg: Type)(implicit ctx: Context): Type = appliedTo(arg :: Nil)
diff --git a/src/dotty/tools/dotc/core/TypeComparer.scala b/src/dotty/tools/dotc/core/TypeComparer.scala
index cab09826b9b8..6174f0915dff 100644
--- a/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -32,6 +32,11 @@ class TypeComparer(initctx: Context) extends DotClass {
    */
   protected var ignoreConstraint = false
 
+  /** Compare a solution of the constraint instead of the constrained parameters.
+   *  The solution maps every parameter to its lower bound.
+   */
+  protected var solvedConstraint = false
+
   private var needsGc = false
 
   /** Is a subtype check in course? In that case we may not
@@ -79,14 +84,89 @@ class TypeComparer(initctx: Context) extends DotClass {
     myAnyType
   }
 
+  /** Map that approximates each param in constraint by its lower bound.
+   *  Currently only used for diagnostics.
+   */
+  val approxParams = new TypeMap {
+    def apply(tp: Type): Type = tp.stripTypeVar match {
+      case tp: PolyParam if constraint contains tp =>
+        this(constraint.bounds(tp).lo)
+      case tp =>
+        mapOver(tp)
+    }
+  }
+
+  /** If `param` is contained in constraint, test whether its
+   *  bounds are non-empty. Otherwise return `true`.
+   */
+  private def checkBounds(param: PolyParam): Boolean = constraint.at(param) match {
+    case TypeBounds(lo, hi) =>
+      if (Stats.monitored) Stats.record("checkBounds")
+      isSubType(lo, hi)
+    case _ => true
+  }
+
+  /** Test validity of constraint for parameter `changed` and of all
+   *  parameters that depend on it.
+   */
+  private def propagate(changed: PolyParam): Boolean =
+    if (Config.trackConstrDeps)
+      checkBounds(changed) &&
+      propagate(constraint.dependentParams(changed) - changed, Set(changed))
+    else
+      constraint forallParams checkBounds
+
+  /** Ensure validity of constraints for parameters `params` and of all
+   *  parameters that depend on them and that have not been tested
+   *  now or before. If `trackConstrDeps` is not set, do this for all
+   *  parameters in the constraint.
+   *  @param  seen  the set of parameters that have been tested before.
+   */
+  private def propagate(params: Set[PolyParam], seen: Set[PolyParam]): Boolean =
+    params.isEmpty ||
+    (params forall checkBounds) && {
+      val seen1 = seen ++ params
+      val nextParams = (Set[PolyParam]() /: params) { (ps, p) =>
+        ps ++ (constraint.dependentParams(p) -- seen1)
+      }
+      propagate(nextParams, seen1)
+    }
+
+  /** Check whether the lower bounds of all parameters in this
+   *  constraint are a solution to the constraint.
+   *  As an optimization, when `trackConstrDeps` is set, we
+   *  only test that the solutions satisfy the constraints `changed`
+   *  and all parameters that depend on it.
+   */
+  def isSatisfiable(changed: PolyParam): Boolean = {
+    val saved = solvedConstraint
+    solvedConstraint = true
+    try
+      if (Config.trackConstrDeps) propagate(changed)
+      else
+        constraint.forallParams { param =>
+          checkBounds(param) || {
+            val TypeBounds(lo, hi) = constraint.bounds(param)
+            ctx.log(i"sub fail $lo <:< $hi")
+            ctx.log(i"approximated = ${approxParams(lo)} <:< ${approxParams(hi)}")
+            false
+          }
+        }
+    finally solvedConstraint = saved
+  }
+
   /** Update constraint for `param` to `bounds`, check that
    *  new constraint is still satisfiable.
    */
   private def updateConstraint(param: PolyParam, bounds: TypeBounds): Boolean = {
     val saved = constraint
     constraint = constraint.updated(param, bounds)
-    isSubType(bounds.lo, bounds.hi) ||
-    { constraint = saved; false } // don't leave the constraint in unsatisfiable state
+    if (propagate(param)) {
+      if (isSatisfiable(param)) return true
+      ctx.log(i"SAT $constraint produced by $param $bounds is not satisfiable")
+    }
+    constraint = saved // don't leave the constraint in unsatisfiable state
+    false
   }
 
   private def addConstraint1(param: PolyParam, bound: Type, fromBelow: Boolean): Boolean = {
@@ -101,7 +181,7 @@ class TypeComparer(initctx: Context) extends DotClass {
       finally ignoreConstraint = saved
     val res =
       (param == bound) || (oldBounds eq newBounds) || updateConstraint(param, newBounds)
-    constr.println(s"add constraint $param ${if (fromBelow) ">:" else "<:"} $bound = $res")
+    constr.println(s"added1 constraint $param ${if (fromBelow) ">:" else "<:"} $bound = $res")
     if (res) constr.println(constraint.show)
     res
   }
@@ -127,7 +207,8 @@ class TypeComparer(initctx: Context) extends DotClass {
   def addConstraint(param: PolyParam, bound0: Type, fromBelow: Boolean): Boolean = {
     assert(!frozenConstraint)
     val bound = bound0.dealias.stripTypeVar
-    constr.println(s"adding ${param.show} ${if (fromBelow) ">:>" else "<:<"} ${bound.show} (${bound.getClass}) to ${constraint.show}")
+    def description = s"${param.show} ${if (fromBelow) ">:>" else "<:<"} ${bound.show} (${bound.getClass}) to ${constraint.show}"
+    constr.println(s"adding $description")
     val res = bound match {
       case bound: PolyParam if constraint contains bound =>
         val TypeBounds(lo, hi) = constraint.bounds(bound)
@@ -150,12 +231,12 @@ class TypeComparer(initctx: Context) extends DotClass {
       case bound => // !!! remove to keep the originals
         addConstraint1(param, bound, fromBelow)
     }
-    constr.println(s"added ${param.show} ${if (fromBelow) ">:>" else "<:<"} ${bound.show} = ${constraint.show}")
+    constr.println(s"added $description = ${constraint.show}")
     res
   }
 
   def isConstrained(param: PolyParam): Boolean =
-    !frozenConstraint && (constraint contains param)
+    !frozenConstraint && !solvedConstraint && (constraint contains param)
 
   /** Solve constraint set for given type parameter `param`.
    *  If `fromBelow` is true the parameter is approximated by its lower bound,
@@ -280,7 +361,7 @@ class TypeComparer(initctx: Context) extends DotClass {
     tp2 match {
       case tp2: NamedType =>
         def compareNamed = {
-          implicit val ctx = this.ctx
+          implicit val ctx: Context = this.ctx // Dotty deviation: implicits need explicit type
           tp1 match {
             case tp1: NamedType =>
               val sym1 = tp1.symbol
@@ -305,13 +386,15 @@ class TypeComparer(initctx: Context) extends DotClass {
       case tp2: ProtoType =>
         isMatchedByProto(tp2, tp1)
       case tp2: PolyParam =>
-        def comparePolyParam = {
-          tp2 == tp1 ||
-            isSubTypeWhenFrozen(tp1, bounds(tp2).lo) || {
-              if (isConstrained(tp2)) addConstraint(tp2, tp1.widen, fromBelow = true)
-              else (ctx.mode is Mode.TypevarsMissContext) || secondTry(tp1, tp2)
-            }
-        }
+        def comparePolyParam =
+          tp2 == tp1 || {
+            if (solvedConstraint && (constraint contains tp2)) isSubType(tp1, bounds(tp2).lo)
+            else
+              isSubTypeWhenFrozen(tp1, bounds(tp2).lo) || {
+                if (isConstrained(tp2)) addConstraint(tp2, tp1.widen, fromBelow = true)
+                else (ctx.mode is Mode.TypevarsMissContext) || secondTry(tp1, tp2)
+              }
+          }
         comparePolyParam
       case tp2: BoundType =>
         tp2 == tp1 || secondTry(tp1, tp2)
@@ -345,23 +428,25 @@ class TypeComparer(initctx: Context) extends DotClass {
     case OrType(tp11, tp12) =>
       isSubType(tp11, tp2) && isSubType(tp12, tp2)
     case tp1: PolyParam =>
-      def comparePolyParam = {
-        tp1 == tp2 ||
-        isSubTypeWhenFrozen(bounds(tp1).hi, tp2) || {
-          if (isConstrained(tp1))
-            addConstraint(tp1, tp2, fromBelow = false) && {
-              if ((!frozenConstraint) &&
-                  (tp2 isRef defn.NothingClass) &&
-                  state.isGlobalCommittable) {
-                def msg = s"!!! instantiated to Nothing: $tp1, constraint = ${constraint.show}"
-                if (Config.flagInstantiationToNothing) assert(false, msg)
-                else ctx.log(msg)
-              }
-              true
+      def comparePolyParam =
+        tp1 == tp2 || {
+          if (solvedConstraint && (constraint contains tp1)) isSubType(bounds(tp1).lo, tp2)
+          else
+            isSubTypeWhenFrozen(bounds(tp1).hi, tp2) || {
+              if (isConstrained(tp1))
+                addConstraint(tp1, tp2, fromBelow = false) && {
+                  if ((!frozenConstraint) &&
+                    (tp2 isRef defn.NothingClass) &&
+                    state.isGlobalCommittable) {
+                    def msg = s"!!! instantiated to Nothing: $tp1, constraint = ${constraint.show}"
+                    if (Config.flagInstantiationToNothing) assert(false, msg)
+                    else ctx.log(msg)
+                  }
+                  true
+                }
+              else (ctx.mode is Mode.TypevarsMissContext) || thirdTry(tp1, tp2)
             }
-          else (ctx.mode is Mode.TypevarsMissContext) || thirdTry(tp1, tp2)
         }
-      }
       comparePolyParam
     case tp1: BoundType =>
       tp1 == tp2 || thirdTry(tp1, tp2)
@@ -590,7 +675,7 @@ class TypeComparer(initctx: Context) extends DotClass {
 
   /** Defer constraining type variables when compared against prototypes */
   def isMatchedByProto(proto: ProtoType, tp: Type) = tp.stripTypeVar match {
-    case tp: PolyParam if constraint contains tp => true
+    case tp: PolyParam if !solvedConstraint && (constraint contains tp) => true
     case _ => proto.isMatchedBy(tp)
   }
 
@@ -612,6 +697,12 @@ class TypeComparer(initctx: Context) extends DotClass {
       i < tparams.length && tparams(i).name == name2
     }
 
+  /** Is type `tp` a TypeRef referring to a higher-kinded parameter? */
+  private def isHKRef(tp: Type) = tp match {
+    case TypeRef(_, name) => name.isHkParamName
+    case _ => false
+  }
+
   /** Can type `tp` be constrained from above by adding a constraint to
    *  a typevar that it refers to? In that case we have to be careful not
    *  to approximate with the lower bound of a type in `thirdTry`. Instead,
@@ -619,7 +710,7 @@ class TypeComparer(initctx: Context) extends DotClass {
    *  type variable with (the corresponding type in) `tp2` instead.
    */
   def isCappable(tp: Type): Boolean = tp match {
-    case tp: PolyParam => constraint contains tp
+    case tp: PolyParam => !solvedConstraint && (constraint contains tp)
     case tp: TypeProxy => isCappable(tp.underlying)
     case tp: AndOrType => isCappable(tp.tp1) || isCappable(tp.tp2)
     case _ => false
@@ -656,7 +747,7 @@ class TypeComparer(initctx: Context) extends DotClass {
         v == 0 || tparam.variance == v
       }
     hk.println(s"isSubTypeHK: args1 = $args1, hk-bounds = $hkBounds $boundsOK $variancesOK")
-    boundsOK && variancesOK
+    boundsOK && variancesOK || fourthTry(tp1, tp2)
   }
 
   def trySetType(tr: NamedType, bounds: TypeBounds): Boolean =
@@ -895,7 +986,11 @@ class TypeComparer(initctx: Context) extends DotClass {
     else {
       val t2 = distributeAnd(tp2, tp1)
       if (t2.exists) t2
-      else AndType(tp1, tp2)
+      else {
+        if (isHKRef(tp1)) tp2
+        else if (isHKRef(tp2)) tp1
+        else AndType(tp1, tp2)
+      }
     }
   }
 
@@ -915,7 +1010,11 @@ class TypeComparer(initctx: Context) extends DotClass {
     else {
       val t2 = distributeOr(tp2, tp1)
       if (t2.exists) t2
-      else OrType(tp1, tp2)
+      else {
+        if (isHKRef(tp1)) tp1
+        else if (isHKRef(tp2)) tp2
+        else OrType(tp1, tp2)
+      }
     }
   }
 
diff --git a/src/dotty/tools/dotc/core/TyperState.scala b/src/dotty/tools/dotc/core/TyperState.scala
index 6e17767d23e2..59c934e0d39d 100644
--- a/src/dotty/tools/dotc/core/TyperState.scala
+++ b/src/dotty/tools/dotc/core/TyperState.scala
@@ -14,7 +14,7 @@ import collection.mutable
 class TyperState(val reporter: Reporter) extends DotClass with Showable {
 
   /** The current constraint set */
-  def constraint: Constraint = new Constraint(SimpleMap.Empty)
+  def constraint: Constraint = new Constraint(SimpleMap.Empty, SimpleMap.Empty)
   def constraint_=(c: Constraint): Unit = {}
 
   /** The uninstantiated variables */
@@ -27,6 +27,9 @@ class TyperState(val reporter: Reporter) extends DotClass with Showable {
    */
   def instType(tvar: TypeVar): Type = constraint.at(tvar.origin) match {
     case _: TypeBounds => NoType
+    case tp: PolyParam =>
+      var tvar1 = constraint.typeVarOfParam(tp)
+      if (tvar1.exists) tvar1 else tp
     case tp => tp
   }
 
@@ -35,6 +38,9 @@ class TyperState(val reporter: Reporter) extends DotClass with Showable {
    */
   def fresh(isCommittable: Boolean): TyperState = this
 
+  /** A fresh type state with the same constraint as this one and the given reporter */
+  def withReporter(reporter: Reporter) = new TyperState(reporter)
+
   /** Commit state so that it gets propagated to enclosing context */
   def commit()(implicit ctx: Context): Unit = unsupported("commit")
 
@@ -42,7 +48,7 @@ class TyperState(val reporter: Reporter) extends DotClass with Showable {
    *  type variable instantiation cannot be retracted anymore. Then, remove
    *  no-longer needed constraint entries.
    */
-  def gc(): Unit = ()
+  def gc()(implicit ctx: Context): Unit = ()
 
   /** Is it allowed to commit this state? */
   def isCommittable: Boolean = false
@@ -64,6 +70,9 @@ extends TyperState(reporter) {
   override def fresh(isCommittable: Boolean): TyperState =
     new MutableTyperState(this, new StoreReporter, isCommittable)
 
+  override def withReporter(reporter: Reporter) =
+    new MutableTyperState(this, reporter, isCommittable)
+
   override val isGlobalCommittable =
     isCommittable &&
     (!previous.isInstanceOf[MutableTyperState] || previous.isGlobalCommittable)
@@ -87,7 +96,7 @@ extends TyperState(reporter) {
     reporter.flush()
   }
 
-  override def gc(): Unit = {
+  override def gc()(implicit ctx: Context): Unit = {
     val toCollect = new mutable.ListBuffer[PolyType]
     constraint foreachTypeVar { tvar =>
       if (!tvar.inst.exists) {
diff --git a/src/dotty/tools/dotc/core/Types.scala b/src/dotty/tools/dotc/core/Types.scala
index 5ce13ad55a98..088a2e3af987 100644
--- a/src/dotty/tools/dotc/core/Types.scala
+++ b/src/dotty/tools/dotc/core/Types.scala
@@ -597,7 +597,7 @@ object Types {
     final def objToAny(implicit ctx: Context) =
       if ((this isRef defn.ObjectClass) && !ctx.phase.erasedTypes) defn.AnyType else this
 
-    /** If this is repeated parameter type, its underlying type,
+    /** If this is repeated parameter type, its underlying Seq type,
      *  else the type itself.
      */
     def underlyingIfRepeated(implicit ctx: Context): Type = this match {
@@ -1314,11 +1314,12 @@ object Types {
       unique(new NonMemberTermRef(prefix, name, sym))
 
     def withSymAndName(prefix: Type, sym: TermSymbol, name: TermName)(implicit ctx: Context): TermRef =
-      if (prefix eq NoPrefix) withNonMemberSym(prefix, name, sym)
-      else {
-        if (sym.defRunId != NoRunId && sym.isCompleted) withSig(prefix, name, sym.signature)
-        else apply(prefix, name)
-      } withSym (sym, Signature.NotAMethod)
+      if (prefix eq NoPrefix)
+        withNonMemberSym(prefix, name, sym)
+      else if (sym.defRunId != NoRunId && sym.isCompleted)
+        withSig(prefix, name, sym.signature) withSym (sym, sym.signature)
+      else
+        apply(prefix, name) withSym (sym, Signature.NotAMethod)
 
     def withSig(prefix: Type, sym: TermSymbol)(implicit ctx: Context): TermRef =
       unique(withSig(prefix, sym.name, sym.signature).withSym(sym, sym.signature))
@@ -1663,9 +1664,15 @@ object Types {
     def apply(paramTypes: List[Type], resultType: Type)(implicit ctx: Context): MethodType =
       apply(nme.syntheticParamNames(paramTypes.length), paramTypes, resultType)
     def fromSymbols(params: List[Symbol], resultType: Type)(implicit ctx: Context) = {
+      def paramInfo(param: Symbol): Type = param.info match {
+        case AnnotatedType(annot, tp) if annot matches defn.RepeatedAnnot =>
+          tp.translateParameterized(defn.SeqClass, defn.RepeatedParamClass)
+        case tp =>
+          tp
+      }
       def transformResult(mt: MethodType) =
         resultType.subst(params, (0 until params.length).toList map (MethodParam(mt, _)))
-      apply(params map (_.name.asTermName), params map (_.info))(transformResult _)
+      apply(params map (_.name.asTermName), params map paramInfo)(transformResult _)
     }
   }
 
@@ -2112,11 +2119,12 @@ object Types {
 
     override def toString =
       if (lo eq hi) s"TypeAlias($lo)" else s"TypeBounds($lo, $hi)"
+
+    override def computeHash = unsupported("computeHash")
   }
 
   class CachedTypeBounds(lo: Type, hi: Type, hc: Int) extends TypeBounds(lo, hi) {
     myHash = hc
-    override def computeHash = unsupported("computeHash")
   }
 
   final class CoTypeBounds(lo: Type, hi: Type, hc: Int) extends CachedTypeBounds(lo, hi, hc) {
@@ -2269,7 +2277,7 @@ object Types {
 
     /** Map this function over given type */
     def mapOver(tp: Type): Type = {
-      implicit val ctx = this.ctx
+      implicit val ctx: Context = this.ctx // Dotty deviation: implicits need explicit type
       tp match {
         case tp: NamedType =>
           if (stopAtStatic && tp.symbol.isStatic) tp
diff --git a/src/dotty/tools/dotc/core/pickling/ClassfileParser.scala b/src/dotty/tools/dotc/core/pickling/ClassfileParser.scala
index f5942dac24b8..0ed301732e8a 100644
--- a/src/dotty/tools/dotc/core/pickling/ClassfileParser.scala
+++ b/src/dotty/tools/dotc/core/pickling/ClassfileParser.scala
@@ -891,8 +891,10 @@ class ClassfileParser(
     def getType(index: Int)(implicit ctx: Context): Type =
       sigToType(getExternalName(index))
 
-    def getSuperClass(index: Int)(implicit ctx: Context): Symbol =
-      if (index == 0) defn.AnyClass else getClassSymbol(index)
+    def getSuperClass(index: Int)(implicit ctx: Context): Symbol = {
+      assert(index != 0, "attempt to parse java.lang.Object from classfile")
+      getClassSymbol(index)
+    }
 
     def getConstant(index: Int)(implicit ctx: Context): Constant = {
       if (index <= 0 || len <= index) errorBadIndex(index)
diff --git a/src/dotty/tools/dotc/core/transform/Erasure.scala b/src/dotty/tools/dotc/core/transform/Erasure.scala
index 9fb580ae8b95..f2e3355fb304 100644
--- a/src/dotty/tools/dotc/core/transform/Erasure.scala
+++ b/src/dotty/tools/dotc/core/transform/Erasure.scala
@@ -61,8 +61,8 @@ object Erasure {
    */
   def transformInfo(sym: Symbol, tp: Type)(implicit ctx: Context): Type = {
     val erase = erasureFn(sym is JavaDefined, isSemi = true, sym.isConstructor, wildcardOK = false)
-    if ((sym eq defn.Object_asInstanceOf) ||
-        (sym eq defn.Object_isInstanceOf) ||
+    if ((sym eq defn.Any_asInstanceOf) ||
+        (sym eq defn.Any_isInstanceOf) ||
         (sym.owner eq defn.ArrayClass) && (sym.isType || sym.isConstructor)) sym.info
     else if (sym.isAbstractType) TypeAlias(WildcardType)
     else erase(tp)
@@ -124,7 +124,7 @@ class Erasure(isJava: Boolean, isSemi: Boolean, isConstructor: Boolean, wildcard
       else this(parent)
     case tp: TermRef =>
       val sym = tp.symbol
-      if (sym.owner is Package) sym.termRef
+      if (sym.exists && (sym.owner is Package)) sym.termRef
       else tp.derivedSelect(this(tp.prefix))
     case _: ThisType | _: ConstantType =>
       tp
diff --git a/src/dotty/tools/dotc/printing/PlainPrinter.scala b/src/dotty/tools/dotc/printing/PlainPrinter.scala
index f10aa7225fcf..308470885fa9 100644
--- a/src/dotty/tools/dotc/printing/PlainPrinter.scala
+++ b/src/dotty/tools/dotc/printing/PlainPrinter.scala
@@ -143,7 +143,7 @@ class PlainPrinter(_ctx: Context) extends Printer {
         toTextLocal(tpe) ~ " " ~ toText(annot)
       case tp: TypeVar =>
         val suffix = if (tp.isInstantiated) "'" else "?"
-        toTextLocal(tp.stripTypeVar) ~ suffix // debug for now, so that we can see where the TypeVars are.
+        toTextLocal(tp.instanceOpt orElse tp.origin) ~ suffix // debug for now, so that we can see where the TypeVars are.
       case _ =>
         tp.fallbackToText(this)
     }
diff --git a/src/dotty/tools/dotc/transform/Erasure.scala b/src/dotty/tools/dotc/transform/Erasure.scala
index 791df341ad09..e6d012d68a6a 100644
--- a/src/dotty/tools/dotc/transform/Erasure.scala
+++ b/src/dotty/tools/dotc/transform/Erasure.scala
@@ -33,7 +33,10 @@ class Erasure extends Phase with DenotTransformer {
   def transform(ref: SingleDenotation)(implicit ctx: Context): SingleDenotation = ref match {
     case ref: SymDenotation =>
       assert(ctx.phase == this, s"transforming $ref at ${ctx.phase}")
-      ref.copySymDenotation(info = transformInfo(ref.symbol, ref.info))
+      val owner = ref.owner
+      ref.copySymDenotation(
+        owner = if (owner eq defn.AnyClass) defn.ObjectClass else owner,
+        info = transformInfo(ref.symbol, ref.info))
     case ref =>
       ref.derivedSingleDenotation(ref.symbol, erasure(ref.info))
   }
@@ -136,7 +139,7 @@ object Erasure {
           cast(runtimeCall(nme.toObjectArray, tree :: Nil), pt)
         case _ =>
           ctx.log(s"casting from ${tree.showSummary}: ${tree.tpe.show} to ${pt.show}")
-          TypeApply(Select(tree, defn.Object_asInstanceOf), TypeTree(pt) :: Nil)
+          TypeApply(Select(tree, defn.Any_asInstanceOf), TypeTree(pt) :: Nil)
       }
 
     /** Adaptation of an expression `e` to an expected type `PT`, applying the following
@@ -195,7 +198,7 @@ object Erasure {
      */
     override def typedSelect(tree: untpd.Select, pt: Type)(implicit ctx: Context): Tree = {
       val sym = tree.symbol
-      assert(sym.exists)
+      assert(sym.exists, tree.show)
 
       def select(qual: Tree, sym: Symbol): Tree =
         untpd.cpy.Select(tree, qual, sym.name) withType qual.tpe.select(sym)
@@ -242,6 +245,8 @@ object Erasure {
         case mt: MethodType =>
           val args1 = args.zipWithConserve(mt.paramTypes)(typedExpr)
           untpd.cpy.Apply(tree, fun1, args1) withType mt.resultType
+        case _ =>
+          throw new MatchError(i"tree $tree has uxpected type of function ${fun1.tpe.widen}, was ${fun.typeOpt.widen}")
       }
     }
 
diff --git a/src/dotty/tools/dotc/transform/InterceptedMethods.scala b/src/dotty/tools/dotc/transform/InterceptedMethods.scala
index d5a4377d049d..f5fed6fda760 100644
--- a/src/dotty/tools/dotc/transform/InterceptedMethods.scala
+++ b/src/dotty/tools/dotc/transform/InterceptedMethods.scala
@@ -28,6 +28,10 @@ import dotty.tools.dotc.core.Denotations.SingleDenotation
 import dotty.tools.dotc.core.SymDenotations.SymDenotation
 import StdNames._
 
+// @DarkDimius The getClass scheme changed. We no longer can have
+// two different methods in Any and Object. The tests pass but I
+// am not sure Intercepted methods treats getClass right now.
+// Please check and delete comment when done.
 /** Replace member references as follows:
   *
   * - `x == y` for == in class Any becomes `x equals y` with equals in class Object.
@@ -50,12 +54,10 @@ class InterceptedMethods extends TreeTransform {
 
   /** perform context-dependant initialization */
   override def init(implicit ctx: Context, info: TransformerInfo): Unit = {
-    getClassMethods =  Set(defn.Any_getClass, defn.AnyVal_getClass)
-    poundPoundMethods = Set(defn.Any_##, defn.Object_##)
+    poundPoundMethods = Set(defn.Any_##)
     Any_comparisons = Set(defn.Any_==, defn.Any_!=)
-    interceptedMethods = getClassMethods ++ poundPoundMethods ++ Any_comparisons
-    primitiveGetClassMethods = Set[Symbol](defn.Any_getClass, defn.AnyVal_getClass) ++
-      defn.ScalaValueClasses.map(x => x.requiredMethod(nme.getClass_))
+    interceptedMethods = poundPoundMethods ++ Any_comparisons
+    primitiveGetClassMethods = Set[Symbol]() ++ defn.ScalaValueClasses.map(x => x.requiredMethod(nme.getClass_))
   }
 
   // this should be removed if we have guarantee that ## will get Apply node
@@ -97,7 +99,7 @@ class InterceptedMethods extends TreeTransform {
 
   override def transformApply(tree: Apply)(implicit ctx: Context, info: TransformerInfo): Tree = {
     def unknown = {
-      assert(false, s"The symbol '${tree.fun.symbol}' was interecepted but didn't match any cases, " +
+      assert(false, s"The symbol '${tree.fun.symbol.showLocated}' was intercepted but didn't match any cases, " +
         s"that means the intercepted methods set doesn't match the code")
       tree
     }
@@ -109,9 +111,9 @@ class InterceptedMethods extends TreeTransform {
             PoundPoundValue(qual)
           } else if (Any_comparisons contains tree.fun.symbol.asTerm) {
             if (tree.fun.symbol eq defn.Any_==) {
-              Apply(Select(qual, defn.Object_equals.termRef), tree.args)
+              Apply(Select(qual, defn.Any_equals), tree.args)
             } else if (tree.fun.symbol eq defn.Any_!=) {
-              Select(Apply(Select(qual, defn.Object_equals.termRef), tree.args), defn.Boolean_!.termRef)
+              Select(Apply(Select(qual, defn.Any_equals), tree.args), defn.Boolean_!)
             } else unknown
           } /* else if (isPrimitiveValueClass(qual.tpe.typeSymbol)) {
             // todo: this is needed to support value classes
@@ -128,7 +130,7 @@ class InterceptedMethods extends TreeTransform {
             //    we get a primitive form of _getClass trying to target a boxed value
             //    so we need replace that method name with Object_getClass to get correct behavior.
             //    See SI-5568.
-            Apply(Select(qual, defn.Object_getClass.termRef), Nil)
+            Apply(Select(qual, defn.Any_getClass), Nil)
           } else {
             unknown
           }
diff --git a/src/dotty/tools/dotc/transform/LazyVals.scala b/src/dotty/tools/dotc/transform/LazyVals.scala
index 9e5ddffa4249..527c7e228965 100644
--- a/src/dotty/tools/dotc/transform/LazyVals.scala
+++ b/src/dotty/tools/dotc/transform/LazyVals.scala
@@ -54,7 +54,7 @@ class LazyValTranformContext {
 
   val infoTransformerNewDefinitions = mutable.Map.empty[ClassSymbol, ListBuffer[Symbol]]
 
-  def addSym(owner: ClassSymbol, sym: Symbol) {
+  def addSym(owner: ClassSymbol, sym: Symbol) = {
     infoTransformerNewDefinitions.get(owner) match {
       case Some(x) => x += sym
       case None => infoTransformerNewDefinitions.put(owner, ListBuffer(sym))
diff --git a/src/dotty/tools/dotc/transform/TailRec.scala b/src/dotty/tools/dotc/transform/TailRec.scala
index b0d5c643834d..cd0643a6e7fe 100644
--- a/src/dotty/tools/dotc/transform/TailRec.scala
+++ b/src/dotty/tools/dotc/transform/TailRec.scala
@@ -129,7 +129,7 @@ class TailRec extends TreeTransform with DenotTransformer {
               Block(
                 List(res),
                 vparamss0.foldLeft(Apply(call, List(This(owner))))
-                  {case (call, args) => Apply(call, args.map(x=> Ident(x.symbol.termRef)))}
+                  {(call, args) => Apply(call, args.map(x => Ident(x.symbol.termRef)))}
                 )
             }
             else {
@@ -213,7 +213,8 @@ class TailRec extends TreeTransform with DenotTransformer {
           val methodWithTargs = if (targs.nonEmpty) TypeApply(method, targs) else method
           if (methodWithTargs.tpe.widen.isParameterless) methodWithTargs
           else argumentss.foldLeft(methodWithTargs) {
-            case (method, args) => Apply(method, args)
+            // case (method, args) => Apply(method, args) // Dotty deviation no auto-detupling yet. Interesting that one can do it in Scala2!
+            (method, args) => Apply(method, args)
           }
         }
         def fail(reason: String) = {
@@ -229,7 +230,7 @@ class TailRec extends TreeTransform with DenotTransformer {
           val recv = noTailTransform(reciever)
           if (recv.tpe.widen.isParameterless) method
           else argumentss.foldLeft(Apply(method, List(recv))) {
-            case (method, args) => Apply(method, args)
+            (method, args) => Apply(method, args) // Dotty deviation no auto-detupling yet.
           }
         }
 
diff --git a/src/dotty/tools/dotc/transform/TreeChecker.scala b/src/dotty/tools/dotc/transform/TreeChecker.scala
index f52c5bc1c94d..e9970e1f88f3 100644
--- a/src/dotty/tools/dotc/transform/TreeChecker.scala
+++ b/src/dotty/tools/dotc/transform/TreeChecker.scala
@@ -8,14 +8,17 @@ import core.SymDenotations._
 import core.Contexts._
 import core.Symbols._
 import core.Types._
+import core.Flags._
 import core.Constants._
 import core.StdNames._
 import core.Decorators._
 import core.transform.Erasure.isUnboundedGeneric
 import typer._
 import typer.ErrorReporting._
+import reporting.ThrowingReporter
 import ast.Trees._
 import ast.{tpd, untpd}
+import java.lang.AssertionError
 
 /** This transform eliminates patterns. Right now it's a dummy.
  *  Awaiting the real pattern matcher.
@@ -25,38 +28,69 @@ class TreeChecker {
 
   def check(ctx: Context) = {
     println(s"checking ${ctx.compilationUnit} after phase ${ctx.phase.prev}")
-    Checker.typedExpr(ctx.compilationUnit.tpdTree)(ctx)
+    val checkingCtx = ctx.fresh
+      .setTyperState(ctx.typerState.withReporter(new ThrowingReporter(ctx.typerState.reporter)))
+    Checker.typedExpr(ctx.compilationUnit.tpdTree)(checkingCtx)
   }
 
   object Checker extends ReTyper {
-    override def typed(tree: untpd.Tree, pt: Type)(implicit ctx: Context) =
-      if (tree.isEmpty) tree.asInstanceOf[Tree]
-      else {
-        assert(tree.hasType, tree.show)
-        val tree1 = super.typed(tree, pt)
-        def sameType(tp1: Type, tp2: Type) =
-          (tp1 eq tp2) || // accept NoType / NoType
-          (tp1 =:= tp2)
-        def divergenceMsg =
-          s"""Types differ
-           |Original type : ${tree.typeOpt.show}
-           |After checking: ${tree1.tpe.show}
-           |Original tree : ${tree.show}
-           |After checking: ${tree1.show}
-        """.stripMargin
-        assert(sameType(tree1.tpe, tree.typeOpt), divergenceMsg)
-        tree1
-      }
+    override def typed(tree: untpd.Tree, pt: Type)(implicit ctx: Context) = try {
+      tree match {
+        case _: untpd.UnApply =>
+          // can't recheck patterns
+          tree.asInstanceOf[tpd.Tree]
+        case _: untpd.TypedSplice | _: untpd.Thicket | _: EmptyValDef[_] =>
+          super.typed(tree)
+        case _ if tree.isType =>
+          promote(tree)
+        case _ =>
+          val tree1 = super.typed(tree, pt)
+          def sameType(tp1: Type, tp2: Type) =
+            (tp1 eq tp2) || // accept NoType / NoType
+            (tp1 =:= tp2)
+          def divergenceMsg =
+            s"""Types differ
+               |Original type : ${tree.typeOpt.show}
+               |After checking: ${tree1.tpe.show}
+               |Original tree : ${tree.show}
+               |After checking: ${tree1.show}
+             """.stripMargin
+          assert(sameType(tree1.tpe, tree.typeOpt), divergenceMsg)
+          tree1
+        }
+    } catch {
+      case ex: Throwable =>
+        println(i"exception while checking $tree of class ${tree.getClass} # ${tree.uniqueId}")
+        throw ex
+    }
 
     override def typedIdent(tree: untpd.Ident, pt: Type)(implicit ctx: Context): Tree = {
-      assert(tree.isTerm, tree.show)
+      assert(tree.isTerm || ctx.phase.prev.id <= ctx.typerPhase.id, tree.show + " at " + ctx.phase)
       super.typedIdent(tree, pt)
     }
 
     override def typedSelect(tree: untpd.Select, pt: Type)(implicit ctx: Context): Tree = {
-      assert(tree.isTerm, tree.show)
+      assert(tree.isTerm || ctx.phase.prev.id <= ctx.typerPhase.id, tree.show + " at " + ctx.phase)
       super.typedSelect(tree, pt)
     }
+
+    /** Check that all defined symbols have legal owners.
+     *  An owner is legal if it is either the same as the context's owner
+     *  or there's an owner chain of valdefs starting at the context's owner and
+     *  reaching up to the symbol's owner. The reason for this relaxed matching
+     *  is that we should be able to pull out an expression as an initializer
+     *  of a helper value without having to do a change owner traversal of the expression.
+     */
+    override def index(trees: List[untpd.Tree])(implicit ctx: Context): Context = {
+      def ownerMatches(symOwner: Symbol, ctxOwner: Symbol): Boolean =
+        symOwner == ctxOwner ||
+        ctxOwner.isTerm && !(ctxOwner is Method | Lazy | Mutable) &&
+          ownerMatches(symOwner, ctxOwner.owner)
+      for (tree <- trees if tree.isDef)
+        assert(ownerMatches(tree.symbol.owner, ctx.owner),
+               i"bad owner; $tree has owner ${tree.symbol.owner}, expected was ${ctx.owner}")
+      super.index(trees)
+    }
   }
 }
 
diff --git a/src/dotty/tools/dotc/transform/TreeTransform.scala b/src/dotty/tools/dotc/transform/TreeTransform.scala
index c0ce68e95469..1bce0de66b57 100644
--- a/src/dotty/tools/dotc/transform/TreeTransform.scala
+++ b/src/dotty/tools/dotc/transform/TreeTransform.scala
@@ -886,32 +886,33 @@ object TreeTransforms {
     final private[TreeTransforms] def transformNamed(tree: NameTree, info: TransformerInfo, cur: Int)(implicit ctx: Context): Tree =
       tree match {
         case tree: Ident =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForIdent, info.nx.nxPrepIdent, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForIdent, info.nx.nxPrepIdent, tree, cur)
+            // Dotty deviation: implicits need explicit type
           if (mutatedInfo eq null) tree
           else goIdent(tree, mutatedInfo.nx.nxTransIdent(cur))
         case tree: Select =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForSelect, info.nx.nxPrepSelect, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForSelect, info.nx.nxPrepSelect, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val qual = transform(tree.qualifier, mutatedInfo, cur)
             goSelect(cpy.Select(tree, qual, tree.name), mutatedInfo.nx.nxTransSelect(cur))
           }
         case tree: SelectFromTypeTree =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForSelectFromTypeTree, info.nx.nxPrepSelectFromTypeTree, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForSelectFromTypeTree, info.nx.nxPrepSelectFromTypeTree, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val qual = transform(tree.qualifier, mutatedInfo, cur)
             goSelectFromTypeTree(cpy.SelectFromTypeTree(tree, qual, tree.name), mutatedInfo.nx.nxTransSelectFromTypeTree(cur))
           }
         case tree: Bind =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForBind, info.nx.nxPrepBind, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForBind, info.nx.nxPrepBind, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val body = transform(tree.body, mutatedInfo, mutatedInfo.nx.nxTransBind(cur))
             goBind(cpy.Bind(tree, tree.name, body), cur)
           }
         case tree: ValDef if !tree.isEmpty => // As a result of discussing with Martin: emptyValDefs shouldn't be copied // NAME
-          implicit val mutatedInfo = mutateTransformers(info, prepForValDef, info.nx.nxPrepValDef, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForValDef, info.nx.nxPrepValDef, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val nestedCtx = if (tree.symbol.exists) localContext(tree.symbol) else ctx
@@ -920,7 +921,7 @@ object TreeTransforms {
             goValDef(cpy.ValDef(tree, tree.mods, tree.name, tpt, rhs), mutatedInfo.nx.nxTransValDef(cur))
           }
         case tree: DefDef =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForDefDef, info.nx.nxPrepDefDef, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForDefDef, info.nx.nxPrepDefDef, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val nestedCtx = localContext(tree.symbol)
@@ -931,7 +932,7 @@ object TreeTransforms {
             goDefDef(cpy.DefDef(tree, tree.mods, tree.name, tparams, vparams, tpt, rhs), mutatedInfo.nx.nxTransDefDef(cur))
           }
         case tree: TypeDef =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForTypeDef, info.nx.nxPrepTypeDef, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForTypeDef, info.nx.nxPrepTypeDef, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val rhs = transform(tree.rhs, mutatedInfo, cur)(localContext(tree.symbol))
@@ -944,18 +945,18 @@ object TreeTransforms {
     final private[TreeTransforms] def transformUnnamed(tree: Tree, info: TransformerInfo, cur: Int)(implicit ctx: Context): Tree =
       tree match {
         case tree: This =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForThis, info.nx.nxPrepThis, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForThis, info.nx.nxPrepThis, tree, cur)
           if (mutatedInfo eq null) tree
           else goThis(tree, mutatedInfo.nx.nxTransThis(cur))
         case tree: Super =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForSuper, info.nx.nxPrepSuper, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForSuper, info.nx.nxPrepSuper, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val qual = transform(tree.qual, mutatedInfo, cur)
             goSuper(cpy.Super(tree, qual, tree.mix), mutatedInfo.nx.nxTransSuper(cur))
           }
         case tree: Apply =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForApply, info.nx.nxPrepApply, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForApply, info.nx.nxPrepApply, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val fun = transform(tree.fun, mutatedInfo, cur)
@@ -963,7 +964,7 @@ object TreeTransforms {
             goApply(cpy.Apply(tree, fun, args), mutatedInfo.nx.nxTransApply(cur))
           }
         case tree: TypeApply =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForTypeApply, info.nx.nxPrepTypeApply, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForTypeApply, info.nx.nxPrepTypeApply, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val fun = transform(tree.fun, mutatedInfo, cur)
@@ -971,18 +972,18 @@ object TreeTransforms {
             goTypeApply(cpy.TypeApply(tree, fun, args), mutatedInfo.nx.nxTransTypeApply(cur))
           }
         case tree: Literal =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForLiteral, info.nx.nxPrepLiteral, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForLiteral, info.nx.nxPrepLiteral, tree, cur)
           if (mutatedInfo eq null) tree
           else goLiteral(tree, mutatedInfo.nx.nxTransLiteral(cur))
         case tree: New =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForNew, info.nx.nxPrepNew, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForNew, info.nx.nxPrepNew, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val tpt = transform(tree.tpt, mutatedInfo, cur)
             goNew(cpy.New(tree, tpt), mutatedInfo.nx.nxTransNew(cur))
           }
         case tree: Pair =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForPair, info.nx.nxPrepPair, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForPair, info.nx.nxPrepPair, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val left = transform(tree.left, mutatedInfo, cur)
@@ -990,7 +991,7 @@ object TreeTransforms {
             goPair(cpy.Pair(tree, left, right), mutatedInfo.nx.nxTransPair(cur))
           }
         case tree: Typed =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForTyped, info.nx.nxPrepTyped, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForTyped, info.nx.nxPrepTyped, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val expr = transform(tree.expr, mutatedInfo, cur)
@@ -998,7 +999,7 @@ object TreeTransforms {
             goTyped(cpy.Typed(tree, expr, tpt), mutatedInfo.nx.nxTransTyped(cur))
           }
         case tree: Assign =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForAssign, info.nx.nxPrepAssign, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForAssign, info.nx.nxPrepAssign, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val lhs = transform(tree.lhs, mutatedInfo, cur)
@@ -1006,7 +1007,7 @@ object TreeTransforms {
             goAssign(cpy.Assign(tree, lhs, rhs), mutatedInfo.nx.nxTransAssign(cur))
           }
         case tree: Block =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForBlock, info.nx.nxPrepBlock, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForBlock, info.nx.nxPrepBlock, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val stats = transformStats(tree.stats, ctx.owner, mutatedInfo, cur)
@@ -1014,7 +1015,7 @@ object TreeTransforms {
             goBlock(cpy.Block(tree, stats, expr), mutatedInfo.nx.nxTransBlock(cur))
           }
         case tree: If =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForIf, info.nx.nxPrepIf, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForIf, info.nx.nxPrepIf, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val cond = transform(tree.cond, mutatedInfo, cur)
@@ -1023,7 +1024,7 @@ object TreeTransforms {
             goIf(cpy.If(tree, cond, thenp, elsep), mutatedInfo.nx.nxTransIf(cur))
           }
         case tree: Closure =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForClosure, info.nx.nxPrepClosure, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForClosure, info.nx.nxPrepClosure, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val env = transformTrees(tree.env, mutatedInfo, cur)
@@ -1032,7 +1033,7 @@ object TreeTransforms {
             goClosure(cpy.Closure(tree, env, meth, tpt), mutatedInfo.nx.nxTransClosure(cur))
           }
         case tree: Match =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForMatch, info.nx.nxPrepMatch, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForMatch, info.nx.nxPrepMatch, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val selector = transform(tree.selector, mutatedInfo, cur)
@@ -1040,7 +1041,7 @@ object TreeTransforms {
             goMatch(cpy.Match(tree, selector, cases), mutatedInfo.nx.nxTransMatch(cur))
           }
         case tree: CaseDef =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForCaseDef, info.nx.nxPrepCaseDef, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForCaseDef, info.nx.nxPrepCaseDef, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val pat = transform(tree.pat, mutatedInfo, cur)
@@ -1049,7 +1050,7 @@ object TreeTransforms {
             goCaseDef(cpy.CaseDef(tree, pat, guard, body), mutatedInfo.nx.nxTransCaseDef(cur))
           }
         case tree: Return =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForReturn, info.nx.nxPrepReturn, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForReturn, info.nx.nxPrepReturn, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val expr = transform(tree.expr, mutatedInfo, cur)
@@ -1057,7 +1058,7 @@ object TreeTransforms {
             goReturn(cpy.Return(tree, expr, from), mutatedInfo.nx.nxTransReturn(cur))
           }
         case tree: Try =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForTry, info.nx.nxPrepTry, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForTry, info.nx.nxPrepTry, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val block = transform(tree.expr, mutatedInfo, cur)
@@ -1066,35 +1067,35 @@ object TreeTransforms {
             goTry(cpy.Try(tree, block, handler, finalizer), mutatedInfo.nx.nxTransTry(cur))
           }
         case tree: Throw =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForThrow, info.nx.nxPrepThrow, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForThrow, info.nx.nxPrepThrow, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val expr = transform(tree.expr, mutatedInfo, cur)
             goThrow(cpy.Throw(tree, expr), mutatedInfo.nx.nxTransThrow(cur))
           }
         case tree: SeqLiteral =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForSeqLiteral, info.nx.nxPrepSeqLiteral, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForSeqLiteral, info.nx.nxPrepSeqLiteral, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val elems = transformTrees(tree.elems, mutatedInfo, cur)
             goSeqLiteral(cpy.SeqLiteral(tree, elems), mutatedInfo.nx.nxTransLiteral(cur))
           }
         case tree: TypeTree =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForTypeTree, info.nx.nxPrepTypeTree, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForTypeTree, info.nx.nxPrepTypeTree, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val original = transform(tree.original, mutatedInfo, cur)
             goTypeTree(cpy.TypeTree(tree, original), mutatedInfo.nx.nxTransTypeTree(cur))
           }
         case tree: Alternative =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForAlternative, info.nx.nxPrepAlternative, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForAlternative, info.nx.nxPrepAlternative, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val trees = transformTrees(tree.trees, mutatedInfo, cur)
             goAlternative(cpy.Alternative(tree, trees), mutatedInfo.nx.nxTransAlternative(cur))
           }
         case tree: UnApply =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForUnApply, info.nx.nxPrepUnApply, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForUnApply, info.nx.nxPrepUnApply, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val fun = transform(tree.fun, mutatedInfo, cur)
@@ -1103,7 +1104,7 @@ object TreeTransforms {
             goUnApply(cpy.UnApply(tree, fun, implicits, patterns), mutatedInfo.nx.nxTransUnApply(cur))
           }
         case tree: Template =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForTemplate, info.nx.nxPrepTemplate, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForTemplate, info.nx.nxPrepTemplate, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val constr = transformSub(tree.constr, mutatedInfo, cur)
@@ -1113,7 +1114,7 @@ object TreeTransforms {
             goTemplate(cpy.Template(tree, constr, parents, self, body), mutatedInfo.nx.nxTransTemplate(cur))
           }
         case tree: PackageDef =>
-          implicit val mutatedInfo = mutateTransformers(info, prepForPackageDef, info.nx.nxPrepPackageDef, tree, cur)
+          implicit val mutatedInfo: TransformerInfo = mutateTransformers(info, prepForPackageDef, info.nx.nxPrepPackageDef, tree, cur)
           if (mutatedInfo eq null) tree
           else {
             val nestedCtx = localContext(tree.symbol)
diff --git a/src/dotty/tools/dotc/transform/TypeTestsCasts.scala b/src/dotty/tools/dotc/transform/TypeTestsCasts.scala
index a36bf6500c40..5f65ee414806 100644
--- a/src/dotty/tools/dotc/transform/TypeTestsCasts.scala
+++ b/src/dotty/tools/dotc/transform/TypeTestsCasts.scala
@@ -68,10 +68,10 @@ class TypeTestsCasts extends TreeTransform {
                 runtimeCall(nme.isArray, arg :: Literal(Constant(ndims)) :: Nil)
               if (ndims == 1) isArrayTest(qual)
               else evalOnce(qual) { qual1 =>
-                mkAnd(derivedTree(qual1, defn.Object_isInstanceOf, qual1.tpe), isArrayTest(qual1))
+                mkAnd(derivedTree(qual1, defn.Any_isInstanceOf, qual1.tpe), isArrayTest(qual1))
               }
             case _ =>
-              derivedTree(expr, defn.Object_isInstanceOf, argType)
+              derivedTree(expr, defn.Any_isInstanceOf, argType)
           }
         }
 
@@ -81,10 +81,10 @@ class TypeTestsCasts extends TreeTransform {
           else if (qualCls.isPrimitiveValueClass) {
             val argCls = argType.classSymbol
             if (argCls.isPrimitiveValueClass) primitiveConversion(qual, argCls)
-            else derivedTree(box(qual), defn.Object_asInstanceOf, argType)
+            else derivedTree(box(qual), defn.Any_asInstanceOf, argType)
           }
           else
-            derivedTree(qual, defn.Object_asInstanceOf, argType)
+            derivedTree(qual, defn.Any_asInstanceOf, argType)
         }
 
         if (sym eq defn.Any_isInstanceOf)
diff --git a/src/dotty/tools/dotc/typer/Checking.scala b/src/dotty/tools/dotc/typer/Checking.scala
index ae325af2a449..5e52c5d7e0cd 100644
--- a/src/dotty/tools/dotc/typer/Checking.scala
+++ b/src/dotty/tools/dotc/typer/Checking.scala
@@ -69,15 +69,6 @@ trait Checking {
       defn.ObjectClass.typeRef
   }
 
-  /** Check that (return) type of implicit definition is not empty */
-  def checkImplicitTptNonEmpty(defTree: untpd.ValOrDefDef)(implicit ctx: Context): Unit = defTree.tpt match {
-    case tpt: untpd.DerivedTypeTree =>
-    case TypeTree(untpd.EmptyTree) =>
-      val resStr = if (defTree.isInstanceOf[untpd.DefDef]) "result " else ""
-      ctx.error(d"${resStr}type of implicit definition needs to be given explicitly", defTree.pos)
-    case _ =>
-  }
-
   /** Check that a non-implicit parameter making up the first parameter section of an
    *  implicit conversion is not a singleton type.
    */
@@ -150,7 +141,6 @@ trait NoChecking extends Checking {
   override def checkStable(tp: Type, pos: Position)(implicit ctx: Context): Unit = ()
   override def checkLegalPrefix(tp: Type, pos: Position)(implicit ctx: Context): Unit = ()
   override def checkClassTypeWithStablePrefix(tp: Type, pos: Position, traitReq: Boolean)(implicit ctx: Context): Type = tp
-  override def checkImplicitTptNonEmpty(defTree: untpd.ValOrDefDef)(implicit ctx: Context): Unit = ()
   override def checkImplicitParamsNotSingletons(vparamss: List[List[ValDef]])(implicit ctx: Context): Unit = ()
   override def checkFeasible(tp: Type, pos: Position, where: => String = "")(implicit ctx: Context): Type = tp
   override def checkNoDoubleDefs(cls: Symbol)(implicit ctx: Context): Unit = ()
diff --git a/src/dotty/tools/dotc/typer/EtaExpansion.scala b/src/dotty/tools/dotc/typer/EtaExpansion.scala
index 099dd943a608..110dc6152932 100644
--- a/src/dotty/tools/dotc/typer/EtaExpansion.scala
+++ b/src/dotty/tools/dotc/typer/EtaExpansion.scala
@@ -116,6 +116,7 @@ object EtaExpansion {
    */
   def etaExpand(tree: Tree, mt: MethodType, xarity: Int)(implicit ctx: Context): untpd.Tree = {
     import untpd._
+    assert(!ctx.isAfterTyper)
     val defs = new mutable.ListBuffer[tpd.Tree]
     val lifted: Tree = TypedSplice(liftApp(defs, tree))
     val paramTypes: List[Tree] =
diff --git a/src/dotty/tools/dotc/typer/Implicits.scala b/src/dotty/tools/dotc/typer/Implicits.scala
index 93876651ac80..a32f552edf51 100644
--- a/src/dotty/tools/dotc/typer/Implicits.scala
+++ b/src/dotty/tools/dotc/typer/Implicits.scala
@@ -65,7 +65,7 @@ object Implicits {
           case tpw =>
             //if (ctx.typer.isApplicable(tp, argType :: Nil, resultType))
             //  println(i"??? $tp is applicable to $this / typeSymbol = ${tpw.typeSymbol}")
-            !tpw.derivesFrom(defn.FunctionClass(1))
+            !tpw.derivesFrom(defn.FunctionClass(1)) || tpw.isRef(defn.PredefConformsClass)
         }
 
         def discardForValueType(tpw: Type): Boolean = tpw match {
@@ -400,6 +400,9 @@ trait Implicits { self: Typer =>
    *  !!! todo: catch potential cycles
    */
   def inferImplicit(pt: Type, argument: Tree, pos: Position)(implicit ctx: Context): SearchResult = track("inferImplicit") {
+    assert(!ctx.isAfterTyper,
+      if (argument.isEmpty) i"missing implicit parameter of type $pt after typer"
+      else i"type error: ${argument.tpe} does not conform to $pt")
     ctx.traceIndented(s"search implicit ${pt.show}, arg = ${argument.show}: ${argument.tpe.show}", implicits, show = true) {
       assert(!pt.isInstanceOf[ExprType])
       val isearch =
@@ -472,7 +475,7 @@ trait Implicits { self: Typer =>
           shadowedImplicit(ref, methPart(shadowing).tpe)
         }
         else
-          SearchSuccess(generated, ref, ctx.typerState)
+          SearchSuccess(generated1, ref, ctx.typerState)
       }}
 
       /** Given a list of implicit references, produce a list of all implicit search successes,
diff --git a/src/dotty/tools/dotc/typer/Namer.scala b/src/dotty/tools/dotc/typer/Namer.scala
index 2d4bf809951c..c3f1dcc81997 100644
--- a/src/dotty/tools/dotc/typer/Namer.scala
+++ b/src/dotty/tools/dotc/typer/Namer.scala
@@ -519,80 +519,92 @@ class Namer { typer: Typer =>
    *                  defined symbol, given its final return type
    */
   def valOrDefDefSig(mdef: ValOrDefDef, sym: Symbol, typeParams: List[Symbol], paramFn: Type => Type)(implicit ctx: Context): Type = {
-    val pt =
-      if (!mdef.tpt.isEmpty) WildcardType
-      else {
 
-        /** An type for this definition that might be inherited from elsewhere:
-         *  If this is a setter parameter, the corresponding getter type.
-         *  If this is a class member, the conjunction of all result types
-         *  of overridden methods.
-         *  NoType if neither case holds.
-         */
-        val inherited =
-          if (sym.owner.isTerm) NoType
-          else {
-            // TODO: Look only at member of supertype instead?
-            lazy val schema = paramFn(WildcardType)
-            val site = sym.owner.thisType
-            ((NoType: Type) /: sym.owner.info.baseClasses.tail) { (tp, cls) =>
-              val iRawInfo =
-                cls.info.nonPrivateDecl(sym.name).matchingDenotation(site, schema).info
-              val iInstInfo = iRawInfo match {
-                case iRawInfo: PolyType =>
-                  if (iRawInfo.paramNames.length == typeParams.length)
-                    iRawInfo.instantiate(typeParams map (_.typeRef))
-                  else NoType
-                case _ =>
-                  if (typeParams.isEmpty) iRawInfo
-                  else NoType
-              }
-              val iResType = iInstInfo.finalResultType.asSeenFrom(site, cls)
-              if (iResType.exists)
-                typr.println(s"using inherited type; raw: $iRawInfo, inst: $iInstInfo, inherited: $iResType")
-              tp & iResType
+    def inferredType = {
+      /** A type for this definition that might be inherited from elsewhere:
+       *  If this is a setter parameter, the corresponding getter type.
+       *  If this is a class member, the conjunction of all result types
+       *  of overridden methods.
+       *  NoType if neither case holds.
+       */
+      val inherited =
+        if (sym.owner.isTerm) NoType
+        else {
+          // TODO: Look only at member of supertype instead?
+          lazy val schema = paramFn(WildcardType)
+          val site = sym.owner.thisType
+          ((NoType: Type) /: sym.owner.info.baseClasses.tail) { (tp, cls) =>
+            val iRawInfo =
+              cls.info.nonPrivateDecl(sym.name).matchingDenotation(site, schema).info
+            val iInstInfo = iRawInfo match {
+              case iRawInfo: PolyType =>
+                if (iRawInfo.paramNames.length == typeParams.length)
+                  iRawInfo.instantiate(typeParams map (_.typeRef))
+                else NoType
+              case _ =>
+                if (typeParams.isEmpty) iRawInfo
+                else NoType
             }
+            val iResType = iInstInfo.finalResultType.asSeenFrom(site, cls)
+            if (iResType.exists)
+              typr.println(s"using inherited type; raw: $iRawInfo, inst: $iInstInfo, inherited: $iResType")
+            tp & iResType
           }
+        }
 
-        /** The proto-type to be used when inferring the result type from
-         *  the right hand side. This is `WildcardType` except if the definition
-         *  is a default getter. In that case, the proto-type is the type of
-         *  the corresponding parameter where bound parameters are replaced by
-         *  Wildcards.
-         */
-        def rhsProto = {
-          val name = sym.asTerm.name
-          val idx = name.defaultGetterIndex
-          if (idx < 0) WildcardType
-          else {
-            val original = name.defaultGetterToMethod
-            val meth: Denotation =
-              if (original.isConstructorName && (sym.owner is ModuleClass))
-                sym.owner.companionClass.info.decl(nme.CONSTRUCTOR)
-              else
-                ctx.defContext(sym).denotNamed(original)
-            def paramProto(paramss: List[List[Type]], idx: Int): Type = paramss match {
-              case params :: paramss1 =>
-                if (idx < params.length) wildApprox(params(idx))
-                else paramProto(paramss1, idx - params.length)
-              case nil =>
-                WildcardType
-            }
-            val defaultAlts = meth.altsWith(_.hasDefaultParams)
-            if (defaultAlts.length == 1)
-              paramProto(defaultAlts.head.info.widen.paramTypess, idx)
+      /** The proto-type to be used when inferring the result type from
+       *  the right hand side. This is `WildcardType` except if the definition
+       *  is a default getter. In that case, the proto-type is the type of
+       *  the corresponding parameter where bound parameters are replaced by
+       *  Wildcards.
+       */
+      def rhsProto = {
+        val name = sym.asTerm.name
+        val idx = name.defaultGetterIndex
+        if (idx < 0) WildcardType
+        else {
+          val original = name.defaultGetterToMethod
+          val meth: Denotation =
+            if (original.isConstructorName && (sym.owner is ModuleClass))
+              sym.owner.companionClass.info.decl(nme.CONSTRUCTOR)
             else
+              ctx.defContext(sym).denotNamed(original)
+          def paramProto(paramss: List[List[Type]], idx: Int): Type = paramss match {
+            case params :: paramss1 =>
+              if (idx < params.length) wildApprox(params(idx))
+              else paramProto(paramss1, idx - params.length)
+            case nil =>
               WildcardType
           }
+          val defaultAlts = meth.altsWith(_.hasDefaultParams)
+          if (defaultAlts.length == 1)
+            paramProto(defaultAlts.head.info.widen.paramTypess, idx)
+          else
+            WildcardType
         }
+      }
 
-        // println(s"final inherited for $sym: ${inherited.toString}") !!!
-        // println(s"owner = ${sym.owner}, decls = ${sym.owner.info.decls.show}")
-        val rhsCtx = ctx.fresh addMode Mode.InferringReturnType
-        def rhsType = typedAheadExpr(mdef.rhs, rhsProto)(rhsCtx).tpe.widen.approximateUnion
-        def lhsType = fullyDefinedType(rhsType, "right-hand side", mdef.pos)
-        inherited orElse lhsType orElse WildcardType
+      // println(s"final inherited for $sym: ${inherited.toString}") !!!
+      // println(s"owner = ${sym.owner}, decls = ${sym.owner.info.decls.show}")
+      val rhsCtx = ctx.fresh addMode Mode.InferringReturnType
+      def rhsType = typedAheadExpr(mdef.rhs, rhsProto)(rhsCtx).tpe.widen.approximateUnion
+      def lhsType = fullyDefinedType(rhsType, "right-hand side", mdef.pos)
+      if (inherited.exists) inherited
+      else {
+        if (sym is Implicit) {
+          val resStr = if (mdef.isInstanceOf[DefDef]) "result " else ""
+          ctx.error(d"${resStr}type of implicit definition needs to be given explicitly", mdef.pos)
+          sym.resetFlag(Implicit)
+        }
+        lhsType orElse WildcardType
       }
+    }
+
+    val pt = mdef.tpt match {
+      case _: untpd.DerivedTypeTree => WildcardType
+      case TypeTree(untpd.EmptyTree) => inferredType
+      case _ => WildcardType
+    }
     paramFn(typedAheadType(mdef.tpt, pt).tpe)
   }
 
diff --git a/src/dotty/tools/dotc/typer/ProtoTypes.scala b/src/dotty/tools/dotc/typer/ProtoTypes.scala
index aeba02648da1..4aba4fb59ac4 100644
--- a/src/dotty/tools/dotc/typer/ProtoTypes.scala
+++ b/src/dotty/tools/dotc/typer/ProtoTypes.scala
@@ -46,7 +46,7 @@ object ProtoTypes {
      *  fits the given expected result type.
      */
     def constrainResult(mt: Type, pt: Type)(implicit ctx: Context): Boolean = pt match {
-      case FunProto(_, result, _) =>
+      case _: FunProto =>
         mt match {
           case mt: MethodType =>
             mt.isDependent || constrainResult(mt.resultType, pt.resultType)
@@ -60,6 +60,8 @@ object ProtoTypes {
           case _ =>
             isCompatible(mt, pt)
         }
+      case _: WildcardType =>
+        isCompatible(mt, pt)
       case _ =>
         true
     }
@@ -217,9 +219,8 @@ object ProtoTypes {
    */
   abstract case class ViewProto(argType: Type, override val resultType: Type)(implicit ctx: Context)
   extends CachedGroundType with ApplyingProto {
-    def isMatchedBy(tp: Type)(implicit ctx: Context): Boolean = /*ctx.conditionalTraceIndented(lookingForInfo, i"?.info isMatchedBy $tp ${tp.getClass}")*/ {
+    def isMatchedBy(tp: Type)(implicit ctx: Context): Boolean =
   	  ctx.typer.isApplicable(tp, argType :: Nil, resultType)
-    }
 
     def derivedViewProto(argType: Type, resultType: Type)(implicit ctx: Context) =
       if ((argType eq this.argType) && (resultType eq this.resultType)) this
@@ -352,17 +353,15 @@ object ProtoTypes {
       tp.derivedRefinedType(wildApprox(tp.parent, theMap), tp.refinedName, wildApprox(tp.refinedInfo, theMap))
     case tp: TypeBounds if tp.lo eq tp.hi => // default case, inlined for speed
       tp.derivedTypeAlias(wildApprox(tp.lo, theMap))
-    case PolyParam(pt, pnum) =>
-      WildcardType(wildApprox(pt.paramBounds(pnum)).bounds)
+    case tp @ PolyParam(poly, pnum) =>
+      ctx.typerState.constraint.at(tp) match {
+        case bounds: TypeBounds => wildApprox(WildcardType(bounds))
+        case _ => WildcardType(wildApprox(poly.paramBounds(pnum)).bounds)
+      }
     case MethodParam(mt, pnum) =>
       WildcardType(TypeBounds.upper(wildApprox(mt.paramTypes(pnum))))
     case tp: TypeVar =>
-      val inst = tp.instanceOpt
-      if (inst.exists) wildApprox(inst)
-      else ctx.typerState.constraint.at(tp.origin) match {
-        case bounds: TypeBounds => wildApprox(WildcardType(bounds))
-        case NoType => WildcardType
-      }
+      wildApprox(tp.underlying)
     case tp: AndType =>
       val tp1a = wildApprox(tp.tp1)
       val tp2a = wildApprox(tp.tp2)
diff --git a/src/dotty/tools/dotc/typer/ReTyper.scala b/src/dotty/tools/dotc/typer/ReTyper.scala
index c2f627b1e7b9..76817fd16cb6 100644
--- a/src/dotty/tools/dotc/typer/ReTyper.scala
+++ b/src/dotty/tools/dotc/typer/ReTyper.scala
@@ -4,6 +4,7 @@ package typer
 import core.Contexts._
 import core.Types._
 import core.Symbols._
+import core.Decorators._
 import typer.ProtoTypes._
 import ast.{tpd, untpd}
 import ast.Trees._
@@ -20,7 +21,7 @@ class ReTyper extends Typer {
   import tpd._
 
   protected def promote(tree: untpd.Tree)(implicit ctx: Context): tree.ThisTree[Type] = {
-    assert(tree.hasType)
+    assert(tree.hasType, i"$tree ${tree.getClass} ${tree.uniqueId}")
     tree.withType(tree.typeOpt)
   }
 
@@ -39,6 +40,9 @@ class ReTyper extends Typer {
     untpd.cpy.SelectFromTypeTree(tree, qual1, tree.name).withType(tree.typeOpt)
   }
 
+  override def typedLiteral(tree: untpd.Literal)(implicit ctc: Context): Literal =
+    promote(tree)
+
   override def typedTypeTree(tree: untpd.TypeTree, pt: Type)(implicit ctx: Context): TypeTree =
     promote(tree)
 
diff --git a/src/dotty/tools/dotc/typer/TypeAssigner.scala b/src/dotty/tools/dotc/typer/TypeAssigner.scala
index 12f2415d89da..13f65d42491f 100644
--- a/src/dotty/tools/dotc/typer/TypeAssigner.scala
+++ b/src/dotty/tools/dotc/typer/TypeAssigner.scala
@@ -166,17 +166,14 @@ trait TypeAssigner {
    *   - any further information it needs to access to compute that type.
    */
 
-  def assignType(tree: untpd.Ident, rawType: Type)(implicit ctx: Context) = {
-    tree.withType(if (tree.isType) rawType else rawType.underlyingIfRepeated)
-  }
+  def assignType(tree: untpd.Ident, tp: Type)(implicit ctx: Context) =
+    tree.withType(tp)
 
-  def assignType(tree: untpd.Select, qual: Tree)(implicit ctx: Context) = {
+  def assignType(tree: untpd.Select, qual: Tree)(implicit ctx: Context) =
     tree.withType(accessibleSelectionType(tree, qual))
-  }
 
-  def assignType(tree: untpd.SelectFromTypeTree, qual: Tree)(implicit ctx: Context) = {
+  def assignType(tree: untpd.SelectFromTypeTree, qual: Tree)(implicit ctx: Context) =
     tree.withType(accessibleSelectionType(tree, qual))
-  }
 
   def assignType(tree: untpd.New, tpt: Tree)(implicit ctx: Context) =
     tree.withType(tpt.tpe)
diff --git a/src/dotty/tools/dotc/typer/Typer.scala b/src/dotty/tools/dotc/typer/Typer.scala
index e4acff53631d..f4b52ce09d16 100644
--- a/src/dotty/tools/dotc/typer/Typer.scala
+++ b/src/dotty/tools/dotc/typer/Typer.scala
@@ -260,7 +260,7 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
         error(d"not found: $kind$name", tree.pos)
         ErrorType
       }
-    checkValue(tree.withType(ownType.underlyingIfRepeated), pt)
+    checkValue(tree.withType(ownType), pt)
   }
 
   def typedSelect(tree: untpd.Select, pt: Type)(implicit ctx: Context): Tree = track("typedSelect") {
@@ -753,7 +753,6 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
     val ValDef(mods, name, tpt, rhs) = vdef
     val mods1 = typedModifiers(mods, sym)
     val tpt1 = typedType(tpt)
-    if ((sym is Implicit) && sym.owner.isType) checkImplicitTptNonEmpty(vdef)
     val rhs1 = rhs match {
       case Ident(nme.WILDCARD) => rhs withType tpt1.tpe
       case _ => typedExpr(rhs, tpt1.tpe)
@@ -766,10 +765,7 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
     val mods1 = typedModifiers(mods, sym)
     val tparams1 = tparams mapconserve (typed(_).asInstanceOf[TypeDef])
     val vparamss1 = vparamss nestedMapconserve (typed(_).asInstanceOf[ValDef])
-    if (sym is Implicit) {
-      if (sym.owner.isType) checkImplicitTptNonEmpty(ddef)
-      checkImplicitParamsNotSingletons(vparamss1)
-    }
+    if (sym is Implicit) checkImplicitParamsNotSingletons(vparamss1)
     val tpt1 = typedType(tpt)
     val rhs1 = typedExpr(rhs, tpt1.tpe)
     assignType(cpy.DefDef(ddef, mods1, name, tparams1, vparamss1, tpt1, rhs1), sym)
@@ -1137,7 +1133,7 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
           def where = d"parameter $pname of $methodStr"
           inferImplicit(formal, EmptyTree, tree.pos.endPos) match {
             case SearchSuccess(arg, _, _) =>
-              arg
+              adapt(arg, formal)
             case ambi: AmbiguousImplicits =>
               implicitArgError(s"ambiguous implicits: ${ambi.explanation} of $where")
             case failure: SearchFailure =>
diff --git a/test/dotc/comptest.scala b/test/dotc/comptest.scala
index e7f60488b89d..63c4003047f3 100644
--- a/test/dotc/comptest.scala
+++ b/test/dotc/comptest.scala
@@ -15,7 +15,7 @@ object comptest extends CompilerTest {
       dotcDir + "tools/dotc/ast/Trees.scala",
       "#runs", "2",
       "-Ylog:frontend",
-      "-Xprompt"))
+      "-Xprompt"))(Nil)
 
 //    compileDir(dotcDir + "tools/dotc/printing", List("-Xprompt", "-Ylog:frontend", "#runs", "2", "-uniqid"))
 }
diff --git a/test/dotc/tests.scala b/test/dotc/tests.scala
index c6fbcabf4eb6..31ab15b57b91 100644
--- a/test/dotc/tests.scala
+++ b/test/dotc/tests.scala
@@ -5,15 +5,18 @@ import test._
 
 class tests extends CompilerTest {
 
-  override val defaultOptions =
-    List(
+  val noCheckOptions = List(
 //        "-verbose",
 //         "-Ylog:frontend",
 //        "-Xprompt",
 //        "-explaintypes",
 //        "-Yshow-suppressed-errors",
-        "-pagewidth", "160"
-    )
+        "-pagewidth", "160")
+
+  implicit val defaultOptions = noCheckOptions ++ List(
+    "-Ycheck:front"//, "-Ystop-before:terminal"
+  )
+
   val twice = List("#runs", "2", "-YnoDoubleBindings")
   val doErase = List("-Ystop-before:terminal")
 
@@ -68,7 +71,10 @@ class tests extends CompilerTest {
   @Test def neg_i50_volatile = compileFile(negDir, "i50-volatile", xerrors = 4)
   @Test def neg_t0273_doubledefs = compileFile(negDir, "t0273", xerrors = 1)
   @Test def neg_t0586_structural = compileFile(negDir, "t0586", xerrors = 1)
-  @Test def neg_t0625_structural = compileFile(negDir, "t0625", xerrors = 1)
+  @Test def neg_t0625_structural = compileFile(negDir, "t0625", xerrors = 1)(
+      defaultOptions = noCheckOptions)
+        // -Ycheck fails because there are structural types involving higher-kinded types.
+        // these are illegal, but are tested only later.
   @Test def neg_t0654_polyalias = compileFile(negDir, "t0654", xerrors = 2)
   @Test def neg_t1192_legalPrefix = compileFile(negDir, "t1192", xerrors = 1)
   @Test def neg_tailcall_t1672b = compileFile(negDir, "tailcall/t1672b", xerrors = 6)
@@ -83,7 +89,8 @@ class tests extends CompilerTest {
   @Test def dotc_config = compileDir(dotcDir + "tools/dotc/config", twice)
   @Test def dotc_core = compileDir(dotcDir + "tools/dotc/core", twice)
   @Test def dotc_core_pickling = compileDir(dotcDir + "tools/dotc/core/pickling", twice)
-  @Test def dotc_transform = compileDir(dotcDir + "tools/dotc/core/transform", twice)
+  @Test def dotc_core_transform = compileDir(dotcDir + "tools/dotc/core/transform", twice)
+  @Test def dotc_transform = compileDir(dotcDir + "tools/dotc/transform", twice)
   @Test def dotc_parsing = compileDir(dotcDir + "tools/dotc/parsing", twice)
   @Test def dotc_printing = compileDir(dotcDir + "tools/dotc/printing", twice)
   @Test def dotc_reporting = compileDir(dotcDir + "tools/dotc/reporting", twice)
diff --git a/test/test/CompilerTest.scala b/test/test/CompilerTest.scala
index d52e74de7b9e..1bf138d54920 100644
--- a/test/test/CompilerTest.scala
+++ b/test/test/CompilerTest.scala
@@ -8,29 +8,27 @@ import dotty.tools.dotc.reporting.Reporter
 
 class CompilerTest extends DottyTest {
 
-  def defaultOptions: List[String] = Nil
-
-  def compileArgs(args: Array[String], xerrors: Int = 0): Unit = {
+  def compileArgs(args: Array[String], xerrors: Int = 0)(implicit defaultOptions: List[String]): Unit = {
     val allArgs = args ++ defaultOptions
     val processor = if (allArgs.exists(_.startsWith("#"))) Bench else Main
     val nerrors = processor.process(allArgs, ctx).count(Reporter.ERROR.level)
     assert(nerrors == xerrors, s"Wrong # of errors. Expected: $xerrors, found: $nerrors")
   }
 
-  def compileLine(cmdLine: String, xerrors: Int = 0): Unit = compileArgs(cmdLine.split("\n"), xerrors)
+  def compileLine(cmdLine: String, xerrors: Int = 0)(implicit defaultOptions: List[String]): Unit = compileArgs(cmdLine.split("\n"), xerrors)
 
-  def compileFile(prefix: String, fileName: String, args: List[String] = Nil, xerrors: Int = 0): Unit =
+  def compileFile(prefix: String, fileName: String, args: List[String] = Nil, xerrors: Int = 0)(implicit defaultOptions: List[String]): Unit =
     compileArgs((s"$prefix$fileName.scala" :: args).toArray, xerrors)
 
-  def compileDir(path: String, args: List[String] = Nil, xerrors: Int = 0): Unit =
+  def compileDir(path: String, args: List[String] = Nil, xerrors: Int = 0)(implicit defaultOptions: List[String]): Unit =
     compileDir(Directory(path), args, xerrors)
 
-  def compileDir(dir: Directory, args: List[String], xerrors: Int): Unit = {
+  def compileDir(dir: Directory, args: List[String], xerrors: Int)(implicit defaultOptions: List[String]): Unit = {
     val fileNames = dir.files.toArray.map(_.toString).filter(_ endsWith ".scala")
     compileArgs(fileNames ++ args, xerrors)
   }
 
-  def compileFiles(path: String, args: List[String] = Nil): Unit = {
+  def compileFiles(path: String, args: List[String] = Nil)(implicit defaultOptions: List[String]): Unit = {
     val dir = Directory(path)
     val fileNames = dir.files.toArray.map(_.toString).filter(_ endsWith ".scala")
     for (name <- fileNames) {
@@ -43,7 +41,7 @@ class CompilerTest extends DottyTest {
     }
   }
 }
-object CompilerText extends App {
+object CompilerTest extends App {
 
 //  val dotcDir = "/Users/odersky/workspace/dotty/src/dotty/"
 
diff --git a/test/test/transform/LazyValsTest.scala b/test/test/transform/LazyValsTest.scala
index 98853ad60078..30c093f70eb1 100644
--- a/test/test/transform/LazyValsTest.scala
+++ b/test/test/transform/LazyValsTest.scala
@@ -183,8 +183,9 @@ class LazyValsTest extends DottyTest {
         (tree, ctx) =>
           val accessor = "DefDef(Modifiers(,,List(Apply(Select(New(Ident(volatile)),<init>),List()))),s,List(),List(),TypeTree[TypeRef(ThisType(module class lang),String)],Block(List(ValDef(Modifiers(,,List()),result,TypeTree[TermRef(ThisType(class LV),s)],Literal(Constant(null))), ValDef(Modifiers(,,List()),retry,TypeTree[TypeRef(ThisType(module class scala),Boolean)],Literal(Constant(true))), ValDef(Modifiers(,,List()),flag,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0))), WhileDo(Ident(retry),Block(List(Assign(Ident(flag),Apply(Select(Ident(LazyVals),get),List(This(LV), Select(Ident(LV),OFFSET$0))))),Match(Apply(Select(Ident(LazyVals),STATE),List(Ident(flag), Literal(Constant(0)))),List(CaseDef(Literal(Constant(0)),EmptyTree,If(Apply(Select(Ident(LazyVals),CAS),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(1)), Literal(Constant(0)))),Block(List(Try(Assign(Ident(result),Literal(Constant(a))),Block(List(DefDef(Modifiers(,,List()),$anonfun,List(),List(List(ValDef(Modifiers(,,List()),x$1,TypeTree[TypeRef(ThisType(module class lang),Throwable)],EmptyTree))),TypeTree[TypeRef(ThisType(module class scala),Int)],Block(List(Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(0)), Literal(Constant(0))))),Throw(Ident(x$1))))),Closure(List(),Ident($anonfun),EmptyTree)),EmptyTree), Assign(Ident(s$lzy1),Ident(result)), Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(3)), Literal(Constant(0)))), Assign(Ident(retry),Literal(Constant(false)))),Literal(Constant(()))),Literal(Constant(())))), CaseDef(Literal(Constant(1)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(2)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(3)),EmptyTree,Block(List(Assign(Ident(retry),Literal(Constant(false))), Assign(Ident(result),Ident(s$lzy1))),Literal(Constant(()))))))))),Ident(result)))"
           val fields = "ValDef(Modifiers(,,List()),s$lzy1,TypeTree[TypeRef(ThisType(module class lang),String)],Literal(Constant(null))), ValDef(Modifiers(,,List()),bitmap$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0)))"
-          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(TypeTree[TypeRef(ThisType(module class lang),Object)]),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
+          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(Apply(Select(New(TypeTree[TypeRef(ThisType(module class lang),Object)]),<init>),List())),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
           val treeS = tree.toString
+          println(treeS)
           Assert.assertTrue("volatile field lazy ref rewritten to class creation",
             treeS.contains(accessor) && treeS.contains(fields) && treeS.contains(moduleField))
       }
@@ -196,7 +197,7 @@ class LazyValsTest extends DottyTest {
         (tree, ctx) =>
           val accessor = "DefDef(Modifiers(,,List(Apply(Select(New(Ident(volatile)),<init>),List()))),s,List(),List(),TypeTree[TypeRef(ThisType(module class scala),Int)],Block(List(ValDef(Modifiers(,,List()),result,TypeTree[TermRef(ThisType(class LV),s)],Literal(Constant(0))), ValDef(Modifiers(,,List()),retry,TypeTree[TypeRef(ThisType(module class scala),Boolean)],Literal(Constant(true))), ValDef(Modifiers(,,List()),flag,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0))), WhileDo(Ident(retry),Block(List(Assign(Ident(flag),Apply(Select(Ident(LazyVals),get),List(This(LV), Select(Ident(LV),OFFSET$0))))),Match(Apply(Select(Ident(LazyVals),STATE),List(Ident(flag), Literal(Constant(0)))),List(CaseDef(Literal(Constant(0)),EmptyTree,If(Apply(Select(Ident(LazyVals),CAS),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(1)), Literal(Constant(0)))),Block(List(Try(Assign(Ident(result),Literal(Constant(1))),Block(List(DefDef(Modifiers(,,List()),$anonfun,List(),List(List(ValDef(Modifiers(,,List()),x$1,TypeTree[TypeRef(ThisType(module class lang),Throwable)],EmptyTree))),TypeTree[TypeRef(ThisType(module class scala),Int)],Block(List(Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(0)), Literal(Constant(0))))),Throw(Ident(x$1))))),Closure(List(),Ident($anonfun),EmptyTree)),EmptyTree), Assign(Ident(s$lzy1),Ident(result)), Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(3)), Literal(Constant(0)))), Assign(Ident(retry),Literal(Constant(false)))),Literal(Constant(()))),Literal(Constant(())))), CaseDef(Literal(Constant(1)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(2)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(3)),EmptyTree,Block(List(Assign(Ident(retry),Literal(Constant(false))), Assign(Ident(result),Ident(s$lzy1))),Literal(Constant(()))))))))),Ident(result)))"
           val fields = "ValDef(Modifiers(,,List()),s$lzy1,TypeTree[TypeRef(ThisType(module class scala),Int)],Literal(Constant(0))), ValDef(Modifiers(,,List()),bitmap$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0)))"
-          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(TypeTree[TypeRef(ThisType(module class lang),Object)]),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
+          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(Apply(Select(New(TypeTree[TypeRef(ThisType(module class lang),Object)]),<init>),List())),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
           val treeS = tree.toString
           Assert.assertTrue("volatile field lazy ref rewritten to class creation",
             treeS.contains(accessor) && treeS.contains(fields) && treeS.contains(moduleField))
@@ -209,7 +210,7 @@ class LazyValsTest extends DottyTest {
         (tree, ctx) =>
           val accessor = "DefDef(Modifiers(,,List(Apply(Select(New(Ident(volatile)),<init>),List()))),s,List(),List(),TypeTree[TypeRef(ThisType(module class scala),Long)],Block(List(ValDef(Modifiers(,,List()),result,TypeTree[TermRef(ThisType(class LV),s)],Literal(Constant(0))), ValDef(Modifiers(,,List()),retry,TypeTree[TypeRef(ThisType(module class scala),Boolean)],Literal(Constant(true))), ValDef(Modifiers(,,List()),flag,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0))), WhileDo(Ident(retry),Block(List(Assign(Ident(flag),Apply(Select(Ident(LazyVals),get),List(This(LV), Select(Ident(LV),OFFSET$0))))),Match(Apply(Select(Ident(LazyVals),STATE),List(Ident(flag), Literal(Constant(0)))),List(CaseDef(Literal(Constant(0)),EmptyTree,If(Apply(Select(Ident(LazyVals),CAS),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(1)), Literal(Constant(0)))),Block(List(Try(Assign(Ident(result),Literal(Constant(1))),Block(List(DefDef(Modifiers(,,List()),$anonfun,List(),List(List(ValDef(Modifiers(,,List()),x$1,TypeTree[TypeRef(ThisType(module class lang),Throwable)],EmptyTree))),TypeTree[TypeRef(ThisType(module class scala),Int)],Block(List(Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(0)), Literal(Constant(0))))),Throw(Ident(x$1))))),Closure(List(),Ident($anonfun),EmptyTree)),EmptyTree), Assign(Ident(s$lzy1),Ident(result)), Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(3)), Literal(Constant(0)))), Assign(Ident(retry),Literal(Constant(false)))),Literal(Constant(()))),Literal(Constant(())))), CaseDef(Literal(Constant(1)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(2)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(3)),EmptyTree,Block(List(Assign(Ident(retry),Literal(Constant(false))), Assign(Ident(result),Ident(s$lzy1))),Literal(Constant(()))))))))),Ident(result)))"
           val fields = "ValDef(Modifiers(,,List()),s$lzy1,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0))), ValDef(Modifiers(,,List()),bitmap$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0)))"
-          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(TypeTree[TypeRef(ThisType(module class lang),Object)]),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
+          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(Apply(Select(New(TypeTree[TypeRef(ThisType(module class lang),Object)]),<init>),List())),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
           val treeS = tree.toString
           Assert.assertTrue("volatile field lazy ref rewritten to class creation",
             treeS.contains(accessor) && treeS.contains(fields) && treeS.contains(moduleField))
@@ -222,7 +223,7 @@ class LazyValsTest extends DottyTest {
         (tree, ctx) =>
           val accessor = "DefDef(Modifiers(,,List(Apply(Select(New(Ident(volatile)),<init>),List()))),s,List(),List(),TypeTree[TypeRef(ThisType(module class scala),Float)],Block(List(ValDef(Modifiers(,,List()),result,TypeTree[TermRef(ThisType(class LV),s)],Literal(Constant(0.0))), ValDef(Modifiers(,,List()),retry,TypeTree[TypeRef(ThisType(module class scala),Boolean)],Literal(Constant(true))), ValDef(Modifiers(,,List()),flag,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0))), WhileDo(Ident(retry),Block(List(Assign(Ident(flag),Apply(Select(Ident(LazyVals),get),List(This(LV), Select(Ident(LV),OFFSET$0))))),Match(Apply(Select(Ident(LazyVals),STATE),List(Ident(flag), Literal(Constant(0)))),List(CaseDef(Literal(Constant(0)),EmptyTree,If(Apply(Select(Ident(LazyVals),CAS),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(1)), Literal(Constant(0)))),Block(List(Try(Assign(Ident(result),Literal(Constant(1.0))),Block(List(DefDef(Modifiers(,,List()),$anonfun,List(),List(List(ValDef(Modifiers(,,List()),x$1,TypeTree[TypeRef(ThisType(module class lang),Throwable)],EmptyTree))),TypeTree[TypeRef(ThisType(module class scala),Int)],Block(List(Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(0)), Literal(Constant(0))))),Throw(Ident(x$1))))),Closure(List(),Ident($anonfun),EmptyTree)),EmptyTree), Assign(Ident(s$lzy1),Ident(result)), Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(3)), Literal(Constant(0)))), Assign(Ident(retry),Literal(Constant(false)))),Literal(Constant(()))),Literal(Constant(())))), CaseDef(Literal(Constant(1)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(2)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(3)),EmptyTree,Block(List(Assign(Ident(retry),Literal(Constant(false))), Assign(Ident(result),Ident(s$lzy1))),Literal(Constant(()))))))))),Ident(result)))"
           val fields = "ValDef(Modifiers(,,List()),s$lzy1,TypeTree[TypeRef(ThisType(module class scala),Float)],Literal(Constant(0.0))), ValDef(Modifiers(,,List()),bitmap$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0)))"
-          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(TypeTree[TypeRef(ThisType(module class lang),Object)]),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
+          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(Apply(Select(New(TypeTree[TypeRef(ThisType(module class lang),Object)]),<init>),List())),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
           val treeS = tree.toString
           Assert.assertTrue("volatile field lazy ref rewritten to class creation",
             treeS.contains(accessor) && treeS.contains(fields) && treeS.contains(moduleField))
@@ -235,7 +236,7 @@ class LazyValsTest extends DottyTest {
         (tree, ctx) =>
           val accessor = "DefDef(Modifiers(,,List(Apply(Select(New(Ident(volatile)),<init>),List()))),s,List(),List(),TypeTree[TypeRef(ThisType(module class scala),Double)],Block(List(ValDef(Modifiers(,,List()),result,TypeTree[TermRef(ThisType(class LV),s)],Literal(Constant(0.0))), ValDef(Modifiers(,,List()),retry,TypeTree[TypeRef(ThisType(module class scala),Boolean)],Literal(Constant(true))), ValDef(Modifiers(,,List()),flag,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0))), WhileDo(Ident(retry),Block(List(Assign(Ident(flag),Apply(Select(Ident(LazyVals),get),List(This(LV), Select(Ident(LV),OFFSET$0))))),Match(Apply(Select(Ident(LazyVals),STATE),List(Ident(flag), Literal(Constant(0)))),List(CaseDef(Literal(Constant(0)),EmptyTree,If(Apply(Select(Ident(LazyVals),CAS),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(1)), Literal(Constant(0)))),Block(List(Try(Assign(Ident(result),Literal(Constant(1.0))),Block(List(DefDef(Modifiers(,,List()),$anonfun,List(),List(List(ValDef(Modifiers(,,List()),x$1,TypeTree[TypeRef(ThisType(module class lang),Throwable)],EmptyTree))),TypeTree[TypeRef(ThisType(module class scala),Int)],Block(List(Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(0)), Literal(Constant(0))))),Throw(Ident(x$1))))),Closure(List(),Ident($anonfun),EmptyTree)),EmptyTree), Assign(Ident(s$lzy1),Ident(result)), Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(3)), Literal(Constant(0)))), Assign(Ident(retry),Literal(Constant(false)))),Literal(Constant(()))),Literal(Constant(())))), CaseDef(Literal(Constant(1)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(2)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(3)),EmptyTree,Block(List(Assign(Ident(retry),Literal(Constant(false))), Assign(Ident(result),Ident(s$lzy1))),Literal(Constant(()))))))))),Ident(result)))"
           val fields = "ValDef(Modifiers(,,List()),s$lzy1,TypeTree[TypeRef(ThisType(module class scala),Double)],Literal(Constant(0.0))), ValDef(Modifiers(,,List()),bitmap$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0)))"
-          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(TypeTree[TypeRef(ThisType(module class lang),Object)]),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
+          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(Apply(Select(New(TypeTree[TypeRef(ThisType(module class lang),Object)]),<init>),List())),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
           val treeS = tree.toString
           Assert.assertTrue("volatile field lazy ref rewritten to class creation",
             treeS.contains(accessor) && treeS.contains(fields) && treeS.contains(moduleField))
@@ -248,7 +249,7 @@ class LazyValsTest extends DottyTest {
         (tree, ctx) =>
           val accessor = "DefDef(Modifiers(,,List(Apply(Select(New(Ident(volatile)),<init>),List()))),s,List(),List(),TypeTree[TypeRef(ThisType(module class scala),Boolean)],Block(List(ValDef(Modifiers(,,List()),result,TypeTree[TermRef(ThisType(class LV),s)],Literal(Constant(false))), ValDef(Modifiers(,,List()),retry,TypeTree[TypeRef(ThisType(module class scala),Boolean)],Literal(Constant(true))), ValDef(Modifiers(,,List()),flag,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0))), WhileDo(Ident(retry),Block(List(Assign(Ident(flag),Apply(Select(Ident(LazyVals),get),List(This(LV), Select(Ident(LV),OFFSET$0))))),Match(Apply(Select(Ident(LazyVals),STATE),List(Ident(flag), Literal(Constant(0)))),List(CaseDef(Literal(Constant(0)),EmptyTree,If(Apply(Select(Ident(LazyVals),CAS),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(1)), Literal(Constant(0)))),Block(List(Try(Assign(Ident(result),Literal(Constant(true))),Block(List(DefDef(Modifiers(,,List()),$anonfun,List(),List(List(ValDef(Modifiers(,,List()),x$1,TypeTree[TypeRef(ThisType(module class lang),Throwable)],EmptyTree))),TypeTree[TypeRef(ThisType(module class scala),Int)],Block(List(Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(0)), Literal(Constant(0))))),Throw(Ident(x$1))))),Closure(List(),Ident($anonfun),EmptyTree)),EmptyTree), Assign(Ident(s$lzy1),Ident(result)), Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(3)), Literal(Constant(0)))), Assign(Ident(retry),Literal(Constant(false)))),Literal(Constant(()))),Literal(Constant(())))), CaseDef(Literal(Constant(1)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(2)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(3)),EmptyTree,Block(List(Assign(Ident(retry),Literal(Constant(false))), Assign(Ident(result),Ident(s$lzy1))),Literal(Constant(()))))))))),Ident(result)))"
           val fields = "ValDef(Modifiers(,,List()),s$lzy1,TypeTree[TypeRef(ThisType(module class scala),Boolean)],Literal(Constant(false))), ValDef(Modifiers(,,List()),bitmap$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0)))"
-          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(TypeTree[TypeRef(ThisType(module class lang),Object)]),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
+          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(Apply(Select(New(TypeTree[TypeRef(ThisType(module class lang),Object)]),<init>),List())),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
           val treeS = tree.toString
           Assert.assertTrue("volatile field lazy ref rewritten to class creation",
             treeS.contains(accessor) && treeS.contains(fields) && treeS.contains(moduleField))
@@ -261,7 +262,7 @@ class LazyValsTest extends DottyTest {
         (tree, ctx) =>
           val accessor = "DefDef(Modifiers(,,List(Apply(Select(New(Ident(volatile)),<init>),List()))),s,List(),List(),TypeTree[TypeRef(TermRef(ThisType(module class <root>),scala),Byte)],Block(List(ValDef(Modifiers(,,List()),result,TypeTree[TermRef(ThisType(class LV),s)],Literal(Constant(0))), ValDef(Modifiers(,,List()),retry,TypeTree[TypeRef(ThisType(module class scala),Boolean)],Literal(Constant(true))), ValDef(Modifiers(,,List()),flag,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0))), WhileDo(Ident(retry),Block(List(Assign(Ident(flag),Apply(Select(Ident(LazyVals),get),List(This(LV), Select(Ident(LV),OFFSET$0))))),Match(Apply(Select(Ident(LazyVals),STATE),List(Ident(flag), Literal(Constant(0)))),List(CaseDef(Literal(Constant(0)),EmptyTree,If(Apply(Select(Ident(LazyVals),CAS),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(1)), Literal(Constant(0)))),Block(List(Try(Assign(Ident(result),Literal(Constant(1))),Block(List(DefDef(Modifiers(,,List()),$anonfun,List(),List(List(ValDef(Modifiers(,,List()),x$1,TypeTree[TypeRef(ThisType(module class lang),Throwable)],EmptyTree))),TypeTree[TypeRef(ThisType(module class scala),Int)],Block(List(Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(0)), Literal(Constant(0))))),Throw(Ident(x$1))))),Closure(List(),Ident($anonfun),EmptyTree)),EmptyTree), Assign(Ident(s$lzy1),Ident(result)), Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(3)), Literal(Constant(0)))), Assign(Ident(retry),Literal(Constant(false)))),Literal(Constant(()))),Literal(Constant(())))), CaseDef(Literal(Constant(1)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(2)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(3)),EmptyTree,Block(List(Assign(Ident(retry),Literal(Constant(false))), Assign(Ident(result),Ident(s$lzy1))),Literal(Constant(()))))))))),Ident(result)))"
           val fields = "ValDef(Modifiers(,,List()),s$lzy1,TypeTree[TypeRef(TermRef(ThisType(module class <root>),scala),Byte)],Literal(Constant(0))), ValDef(Modifiers(,,List()),bitmap$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0)))"
-          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(TypeTree[TypeRef(ThisType(module class lang),Object)]),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
+          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(Apply(Select(New(TypeTree[TypeRef(ThisType(module class lang),Object)]),<init>),List())),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
           val treeS = tree.toString
           Assert.assertTrue("volatile field lazy ref rewritten to class creation",
             treeS.contains(accessor) && treeS.contains(fields) && treeS.contains(moduleField))
@@ -274,7 +275,7 @@ class LazyValsTest extends DottyTest {
         (tree, ctx) =>
           val accessor = "DefDef(Modifiers(,,List(Apply(Select(New(Ident(volatile)),<init>),List()))),s,List(),List(),TypeTree[TypeRef(TermRef(ThisType(module class <root>),scala),Short)],Block(List(ValDef(Modifiers(,,List()),result,TypeTree[TermRef(ThisType(class LV),s)],Literal(Constant(0))), ValDef(Modifiers(,,List()),retry,TypeTree[TypeRef(ThisType(module class scala),Boolean)],Literal(Constant(true))), ValDef(Modifiers(,,List()),flag,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0))), WhileDo(Ident(retry),Block(List(Assign(Ident(flag),Apply(Select(Ident(LazyVals),get),List(This(LV), Select(Ident(LV),OFFSET$0))))),Match(Apply(Select(Ident(LazyVals),STATE),List(Ident(flag), Literal(Constant(0)))),List(CaseDef(Literal(Constant(0)),EmptyTree,If(Apply(Select(Ident(LazyVals),CAS),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(1)), Literal(Constant(0)))),Block(List(Try(Assign(Ident(result),Literal(Constant(1))),Block(List(DefDef(Modifiers(,,List()),$anonfun,List(),List(List(ValDef(Modifiers(,,List()),x$1,TypeTree[TypeRef(ThisType(module class lang),Throwable)],EmptyTree))),TypeTree[TypeRef(ThisType(module class scala),Int)],Block(List(Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(0)), Literal(Constant(0))))),Throw(Ident(x$1))))),Closure(List(),Ident($anonfun),EmptyTree)),EmptyTree), Assign(Ident(s$lzy1),Ident(result)), Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(3)), Literal(Constant(0)))), Assign(Ident(retry),Literal(Constant(false)))),Literal(Constant(()))),Literal(Constant(())))), CaseDef(Literal(Constant(1)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(2)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(3)),EmptyTree,Block(List(Assign(Ident(retry),Literal(Constant(false))), Assign(Ident(result),Ident(s$lzy1))),Literal(Constant(()))))))))),Ident(result)))"
           val fields = "ValDef(Modifiers(,,List()),s$lzy1,TypeTree[TypeRef(TermRef(ThisType(module class <root>),scala),Short)],Literal(Constant(0))), ValDef(Modifiers(,,List()),bitmap$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0)))"
-          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(TypeTree[TypeRef(ThisType(module class lang),Object)]),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
+          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(Apply(Select(New(TypeTree[TypeRef(ThisType(module class lang),Object)]),<init>),List())),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
           val treeS = tree.toString
           Assert.assertTrue("volatile field lazy ref rewritten to class creation",
             treeS.contains(accessor) && treeS.contains(fields) && treeS.contains(moduleField))
@@ -287,7 +288,7 @@ class LazyValsTest extends DottyTest {
         (tree, ctx) =>
           val accessor = "DefDef(Modifiers(,,List(Apply(Select(New(Ident(volatile)),<init>),List()))),s,List(),List(),TypeTree[TypeRef(ThisType(module class scala),Char)],Block(List(ValDef(Modifiers(,,List()),result,TypeTree[TermRef(ThisType(class LV),s)],Literal(Constant(\u0000))), ValDef(Modifiers(,,List()),retry,TypeTree[TypeRef(ThisType(module class scala),Boolean)],Literal(Constant(true))), ValDef(Modifiers(,,List()),flag,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0))), WhileDo(Ident(retry),Block(List(Assign(Ident(flag),Apply(Select(Ident(LazyVals),get),List(This(LV), Select(Ident(LV),OFFSET$0))))),Match(Apply(Select(Ident(LazyVals),STATE),List(Ident(flag), Literal(Constant(0)))),List(CaseDef(Literal(Constant(0)),EmptyTree,If(Apply(Select(Ident(LazyVals),CAS),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(1)), Literal(Constant(0)))),Block(List(Try(Assign(Ident(result),Literal(Constant(a))),Block(List(DefDef(Modifiers(,,List()),$anonfun,List(),List(List(ValDef(Modifiers(,,List()),x$1,TypeTree[TypeRef(ThisType(module class lang),Throwable)],EmptyTree))),TypeTree[TypeRef(ThisType(module class scala),Int)],Block(List(Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(0)), Literal(Constant(0))))),Throw(Ident(x$1))))),Closure(List(),Ident($anonfun),EmptyTree)),EmptyTree), Assign(Ident(s$lzy1),Ident(result)), Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(3)), Literal(Constant(0)))), Assign(Ident(retry),Literal(Constant(false)))),Literal(Constant(()))),Literal(Constant(())))), CaseDef(Literal(Constant(1)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(2)),EmptyTree,Apply(Select(Ident(LazyVals),wait4Notification),List(This(LV), Select(Ident(LV),OFFSET$0), Ident(flag), Literal(Constant(0))))), CaseDef(Literal(Constant(3)),EmptyTree,Block(List(Assign(Ident(retry),Literal(Constant(false))), Assign(Ident(result),Ident(s$lzy1))),Literal(Constant(()))))))))),Ident(result)))"
           val fields = "ValDef(Modifiers(,,List()),s$lzy1,TypeTree[TypeRef(ThisType(module class scala),Char)],Literal(Constant(\u0000))), ValDef(Modifiers(,,List()),bitmap$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Literal(Constant(0)))"
-          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(TypeTree[TypeRef(ThisType(module class lang),Object)]),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
+          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(Apply(Select(New(TypeTree[TypeRef(ThisType(module class lang),Object)]),<init>),List())),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
 
           val treeS = tree.toString
           Assert.assertTrue("volatile field lazy ref rewritten to class creation",
@@ -299,7 +300,7 @@ class LazyValsTest extends DottyTest {
     def volatilesReuseBitmaps = {
       checkCompile("LazyVals", "class LV { @volatile lazy val a = 'a'; @volatile lazy val b = 'b';  }") {
         (tree, ctx) =>
-          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(TypeTree[TypeRef(ThisType(module class lang),Object)]),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
+          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(Apply(Select(New(TypeTree[TypeRef(ThisType(module class lang),Object)]),<init>),List())),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
           val reuseFieldPattern = "Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$0), Literal(Constant(3)), Literal(Constant(1))))"
           val treeS = tree.toString
           Assert.assertTrue("volatile field lazy ref rewritten to class creation",
@@ -349,7 +350,7 @@ class LazyValsTest extends DottyTest {
           | }
         """.stripMargin ){
         (tree, ctx) =>
-          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(TypeTree[TypeRef(ThisType(module class lang),Object)]),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$1,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$1))))), ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
+          val moduleField = "TypeDef(Modifiers(final module <synthetic>,,List()),LV$,Template(DefDef(Modifiers(,,List()),<init>,List(),List(List()),TypeTree[TypeRef(ThisType(module class <empty>),LV$)],EmptyTree),List(Apply(Select(New(TypeTree[TypeRef(ThisType(module class lang),Object)]),<init>),List())),ValDef(Modifiers(,,List()),_,TypeTree[TermRef(ThisType(module class <empty>),LV)],EmptyTree),List(ValDef(Modifiers(,,List()),OFFSET$1,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$1))))), ValDef(Modifiers(,,List()),OFFSET$0,TypeTree[TypeRef(ThisType(module class scala),Long)],Apply(Select(Ident(LazyVals),getOffset),List(This(LV), Literal(Constant(bitmap$0))))))))"
           val reuseFieldPattern = "Apply(Select(Ident(LazyVals),setFlag),List(This(LV), Select(Ident(LV),OFFSET$1), Literal(Constant(3)), Literal(Constant(1))))"
           val treeS = tree.toString
           Assert.assertTrue("volatile field lazy ref rewritten to class creation",
diff --git a/tests/neg/tailcall/tailrec-2.scala b/tests/neg/tailcall/tailrec-2.scala
index d6b8b1355b01..bc594293d7f6 100644
--- a/tests/neg/tailcall/tailrec-2.scala
+++ b/tests/neg/tailcall/tailrec-2.scala
@@ -13,7 +13,7 @@ class Bop2[+A](val element: A) extends Super[A] {
   @annotation.tailrec final def f[B >: A](mem: List[B]): List[B] = (null: Bop2[A]).f(mem)
 }
 object Bop3 extends Super[Nothing] {
-  @annotation.tailrec final def f[B](mem: List[B]): List[B] = (null: Bop3.type).f(mem)
+  @annotation.tailrec final def f[B](mem: List[B]): List[B] = (???: Bop3.type).f(mem)
 }
 class Bop4[+A](val element: A) extends Super[A] {
   @annotation.tailrec final def f[B >: A](mem: List[B]): List[B] = Other.f[A].f(mem)
diff --git a/tests/pos/t1164.scala b/tests/pending/pos/t1164.scala
similarity index 100%
rename from tests/pos/t1164.scala
rename to tests/pending/pos/t1164.scala