Move compiler and compiler tests to compiler dir

1 files changed, 636 insertions, 0 deletions

diff --git a/compiler/src/dotty/tools/dotc/core/OrderingConstraint.scala b/compiler/src/dotty/tools/dotc/core/OrderingConstraint.scala
new file mode 100644
index 000000000..72c7a8e51
--- /dev/null
+++ b/compiler/src/dotty/tools/dotc/core/OrderingConstraint.scala
@@ -0,0 +1,636 @@
+package dotty.tools
+package dotc
+package core
+
+import Types._, Contexts._, Symbols._, Decorators._
+import util.SimpleMap
+import collection.mutable
+import printing.{Printer, Showable}
+import printing.Texts._
+import config.Config
+import collection.immutable.BitSet
+import reflect.ClassTag
+import annotation.tailrec
+
+object OrderingConstraint {
+
+  type ArrayValuedMap[T] = SimpleMap[PolyType, Array[T]]
+
+  /** The type of `OrderingConstraint#boundsMap` */
+  type ParamBounds = ArrayValuedMap[Type]
+
+  /** The type of `OrderingConstraint#lowerMap`, `OrderingConstraint#upperMap` */
+  type ParamOrdering = ArrayValuedMap[List[PolyParam]]
+
+  /** A new constraint with given maps */
+  private def newConstraint(boundsMap: ParamBounds, lowerMap: ParamOrdering, upperMap: ParamOrdering)(implicit ctx: Context) : OrderingConstraint = {
+    val result = new OrderingConstraint(boundsMap, lowerMap, upperMap)
+    if (Config.checkConstraintsNonCyclic) result.checkNonCyclic()
+    ctx.runInfo.recordConstraintSize(result, result.boundsMap.size)
+    result
+  }
+
+  /** A lens for updating a single entry array in one of the three constraint maps */
+  abstract class ConstraintLens[T <: AnyRef: ClassTag] {
+    def entries(c: OrderingConstraint, poly: PolyType): Array[T]
+    def updateEntries(c: OrderingConstraint, poly: PolyType, entries: Array[T])(implicit ctx: Context): OrderingConstraint
+    def initial: T
+
+    def apply(c: OrderingConstraint, poly: PolyType, idx: Int) = {
+      val es = entries(c, poly)
+      if (es == null) initial else es(idx)
+    }
+
+    /** The `current` constraint but with the entry for `param` updated to `entry`.
+     *  `current` is used linearly. If it is different from `prev` it is
+     *  known to be dead after the call. Hence it is OK to update destructively
+     *  parts of `current` which are not shared by `prev`.
+     */
+    def update(prev: OrderingConstraint, current: OrderingConstraint,
+        poly: PolyType, idx: Int, entry: T)(implicit ctx: Context): OrderingConstraint = {
+      var es = entries(current, poly)
+      if (es != null && (es(idx) eq entry)) current
+      else {
+        val result =
+          if (es == null) {
+            es = Array.fill(poly.paramNames.length)(initial)
+            updateEntries(current, poly, es)
+          }
+          else if (es ne entries(prev, poly))
+            current // can re-use existing entries array.
+          else {
+            es = es.clone
+            updateEntries(current, poly, es)
+          }
+        es(idx) = entry
+        result
+      }
+    }
+
+    def update(prev: OrderingConstraint, current: OrderingConstraint,
+        param: PolyParam, entry: T)(implicit ctx: Context): OrderingConstraint =
+      update(prev, current, param.binder, param.paramNum, entry)
+
+    def map(prev: OrderingConstraint, current: OrderingConstraint,
+        poly: PolyType, idx: Int, f: T => T)(implicit ctx: Context): OrderingConstraint =
+     update(prev, current, poly, idx, f(apply(current, poly, idx)))
+
+    def map(prev: OrderingConstraint, current: OrderingConstraint,
+        param: PolyParam, f: T => T)(implicit ctx: Context): OrderingConstraint =
+      map(prev, current, param.binder, param.paramNum, f)
+  }
+
+  val boundsLens = new ConstraintLens[Type] {
+    def entries(c: OrderingConstraint, poly: PolyType): Array[Type] =
+      c.boundsMap(poly)
+    def updateEntries(c: OrderingConstraint, poly: PolyType, entries: Array[Type])(implicit ctx: Context): OrderingConstraint =
+      newConstraint(c.boundsMap.updated(poly, entries), c.lowerMap, c.upperMap)
+    def initial = NoType
+  }
+
+  val lowerLens = new ConstraintLens[List[PolyParam]] {
+    def entries(c: OrderingConstraint, poly: PolyType): Array[List[PolyParam]] =
+      c.lowerMap(poly)
+    def updateEntries(c: OrderingConstraint, poly: PolyType, entries: Array[List[PolyParam]])(implicit ctx: Context): OrderingConstraint =
+      newConstraint(c.boundsMap, c.lowerMap.updated(poly, entries), c.upperMap)
+    def initial = Nil
+  }
+
+  val upperLens = new ConstraintLens[List[PolyParam]] {
+    def entries(c: OrderingConstraint, poly: PolyType): Array[List[PolyParam]] =
+      c.upperMap(poly)
+    def updateEntries(c: OrderingConstraint, poly: PolyType, entries: Array[List[PolyParam]])(implicit ctx: Context): OrderingConstraint =
+      newConstraint(c.boundsMap, c.lowerMap, c.upperMap.updated(poly, entries))
+    def initial = Nil
+  }
+}
+
+import OrderingConstraint._
+
+/** Constraint over undetermined type parameters that keeps separate maps to
+ *  reflect parameter orderings.
+ *  @param boundsMap a map from PolyType to arrays.
+ *               Each array contains twice the number of entries as there a type parameters
+ *               in the PolyType. The first half of the array contains the type bounds that constrain the
+ *               polytype's type parameters. The second half might contain type variables that
+ *               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. The dual use of arrays for poly params
+ *               and typevars is to save space and hopefully gain some speed.
+ *
+ *  @param lowerMap a map from PolyTypes to arrays. Each array entry corresponds
+ *               to a parameter P of the polytype; it contains all constrained parameters
+ *               Q that are known to be smaller than P, i.e. Q <: P.
+ *  @param upperMap a map from PolyTypes to arrays. Each array entry corresponds
+ *               to a parameter P of the polytype; it contains all constrained parameters
+ *               Q that are known to be greater than P, i.e. P <: Q.
+ */
+class OrderingConstraint(private val boundsMap: ParamBounds,
+                         private val lowerMap : ParamOrdering,
+                         private val upperMap : ParamOrdering) extends Constraint {
+
+  type This = OrderingConstraint
+
+// ----------- Basic indices --------------------------------------------------
+
+  /** The number of type parameters in the given entry array */
+  private def paramCount(entries: Array[Type]) = entries.length >> 1
+
+  /** The type variable corresponding to parameter numbered `n`, null if none was created */
+  private def typeVar(entries: Array[Type], n: Int): Type =
+    entries(paramCount(entries) + n)
+
+  /** The `boundsMap` entry corresponding to `param` */
+  def entry(param: PolyParam): Type = {
+    val entries = boundsMap(param.binder)
+    if (entries == null) NoType
+    else entries(param.paramNum)
+  }
+
+// ----------- Contains tests --------------------------------------------------
+
+  def contains(pt: PolyType): Boolean = boundsMap(pt) != null
+
+  def contains(param: PolyParam): Boolean = {
+    val entries = boundsMap(param.binder)
+    entries != null && isBounds(entries(param.paramNum))
+  }
+
+  def contains(tvar: TypeVar): Boolean = {
+    val origin = tvar.origin
+    val entries = boundsMap(origin.binder)
+    val pnum = origin.paramNum
+    entries != null && isBounds(entries(pnum)) && (typeVar(entries, pnum) eq tvar)
+  }
+
+  private def isBounds(tp: Type) = tp.isInstanceOf[TypeBounds]
+
+// ---------- Dependency handling ----------------------------------------------
+
+  def lower(param: PolyParam): List[PolyParam] = lowerLens(this, param.binder, param.paramNum)
+  def upper(param: PolyParam): List[PolyParam] = upperLens(this, param.binder, param.paramNum)
+
+  def minLower(param: PolyParam): List[PolyParam] = {
+    val all = lower(param)
+    all.filterNot(p => all.exists(isLess(p, _)))
+  }
+
+  def minUpper(param: PolyParam): List[PolyParam] = {
+    val all = upper(param)
+    all.filterNot(p => all.exists(isLess(_, p)))
+  }
+
+  def exclusiveLower(param: PolyParam, butNot: PolyParam): List[PolyParam] =
+    lower(param).filterNot(isLess(_, butNot))
+
+  def exclusiveUpper(param: PolyParam, butNot: PolyParam): List[PolyParam] =
+    upper(param).filterNot(isLess(butNot, _))
+
+// ---------- Info related to PolyParams -------------------------------------------
+
+  def isLess(param1: PolyParam, param2: PolyParam): Boolean =
+    upper(param1).contains(param2)
+
+  def nonParamBounds(param: PolyParam): TypeBounds =
+    entry(param).asInstanceOf[TypeBounds]
+
+  def fullLowerBound(param: PolyParam)(implicit ctx: Context): Type =
+    (nonParamBounds(param).lo /: minLower(param))(_ | _)
+
+  def fullUpperBound(param: PolyParam)(implicit ctx: Context): Type =
+    (nonParamBounds(param).hi /: minUpper(param))(_ & _)
+
+  def fullBounds(param: PolyParam)(implicit ctx: Context): TypeBounds =
+    nonParamBounds(param).derivedTypeBounds(fullLowerBound(param), fullUpperBound(param))
+
+  def typeVarOfParam(param: PolyParam): Type = {
+    val entries = boundsMap(param.binder)
+    if (entries == null) NoType
+    else {
+      val tvar = typeVar(entries, param.paramNum)
+      if (tvar != null) tvar else NoType
+    }
+  }
+
+// ---------- Adding PolyTypes --------------------------------------------------
+
+  /** The list of parameters P such that, for a fresh type parameter Q:
+   *
+   *    Q <: tp  implies  Q <: P      and isUpper = true, or
+   *    tp <: Q  implies  P <: Q      and isUpper = false
+   */
+  def dependentParams(tp: Type, isUpper: Boolean): List[PolyParam] = tp match {
+    case param: PolyParam if contains(param) =>
+      param :: (if (isUpper) upper(param) else lower(param))
+    case tp: AndOrType =>
+      val ps1 = dependentParams(tp.tp1, isUpper)
+      val ps2 = dependentParams(tp.tp2, isUpper)
+      if (isUpper == tp.isAnd) ps1.union(ps2) else ps1.intersect(ps2)
+    case _ =>
+      Nil
+  }
+
+  /** The bound type `tp` without constrained parameters which are clearly
+   *  dependent. A parameter in an upper bound is clearly dependent if it appears
+   *  in a hole of a context H given by:
+   *
+   *      H = []
+   *          H & T
+   *          T & H
+   *
+   *  (the idea is that a parameter P in a H context is guaranteed to be a supertype of the
+   *   bounded parameter.)
+   *  Analogously, a parameter in a lower bound is clearly dependent if it appears
+   *  in a hole of a context H given by:
+   *
+   *      L = []
+   *          L | T
+   *          T | L
+   *
+   *  "Clearly dependent" is not synonymous with "dependent" in the sense
+   *  it is defined in `dependentParams`. Dependent parameters are handled
+   *  in `updateEntry`. The idea of stripping off clearly dependent parameters
+   *  and to handle them separately is for efficiency, so that type expressions
+   *  used as bounds become smaller.
+   *
+   *  @param isUpper   If true, `bound` is an upper bound, else a lower bound.
+   */
+  private def stripParams(tp: Type, paramBuf: mutable.ListBuffer[PolyParam],
+      isUpper: Boolean)(implicit ctx: Context): Type = tp match {
+    case param: PolyParam if contains(param) =>
+      if (!paramBuf.contains(param)) paramBuf += param
+      NoType
+    case tp: AndOrType if isUpper == tp.isAnd =>
+      val tp1 = stripParams(tp.tp1, paramBuf, isUpper)
+      val tp2 = stripParams(tp.tp2, paramBuf, isUpper)
+      if (tp1.exists)
+        if (tp2.exists) tp.derivedAndOrType(tp1, tp2)
+        else tp1
+      else tp2
+    case _ =>
+      tp
+  }
+
+  /** The bound type `tp` without clearly dependent parameters.
+   *  A top or bottom type if type consists only of dependent parameters.
+   *  @param isUpper   If true, `bound` is an upper bound, else a lower bound.
+   */
+  private def normalizedType(tp: Type, paramBuf: mutable.ListBuffer[PolyParam],
+      isUpper: Boolean)(implicit ctx: Context): Type =
+    stripParams(tp, paramBuf, isUpper)
+      .orElse(if (isUpper) defn.AnyType else defn.NothingType)
+
+  def add(poly: PolyType, tvars: List[TypeVar])(implicit ctx: Context): This = {
+    assert(!contains(poly))
+    val nparams = poly.paramNames.length
+    val entries1 = new Array[Type](nparams * 2)
+    poly.paramBounds.copyToArray(entries1, 0)
+    tvars.copyToArray(entries1, nparams)
+    newConstraint(boundsMap.updated(poly, entries1), lowerMap, upperMap).init(poly)
+  }
+
+  /** Split dependent parameters off the bounds for parameters in `poly`.
+   *  Update all bounds to be normalized and update ordering to account for
+   *  dependent parameters.
+   */
+  private def init(poly: PolyType)(implicit ctx: Context): This = {
+    var current = this
+    val loBuf, hiBuf = new mutable.ListBuffer[PolyParam]
+    var i = 0
+    while (i < poly.paramNames.length) {
+      val param = PolyParam(poly, i)
+      val bounds = nonParamBounds(param)
+      val lo = normalizedType(bounds.lo, loBuf, isUpper = false)
+      val hi = normalizedType(bounds.hi, hiBuf, isUpper = true)
+      current = updateEntry(current, param, bounds.derivedTypeBounds(lo, hi))
+      current = (current /: loBuf)(order(_, _, param))
+      current = (current /: hiBuf)(order(_, param, _))
+      loBuf.clear()
+      hiBuf.clear()
+      i += 1
+    }
+    if (Config.checkConstraintsNonCyclic) checkNonCyclic()
+    current
+  }
+
+// ---------- Updates ------------------------------------------------------------
+
+  /** Add the fact `param1 <: param2` to the constraint `current` and propagate
+   *  `<:<` relationships between parameters ("edges") but not bounds.
+   */
+  private def order(current: This, param1: PolyParam, param2: PolyParam)(implicit ctx: Context): This =
+    if (param1 == param2 || current.isLess(param1, param2)) this
+    else {
+      assert(contains(param1))
+      assert(contains(param2))
+      val newUpper = param2 :: exclusiveUpper(param2, param1)
+      val newLower = param1 :: exclusiveLower(param1, param2)
+      val current1 = (current /: newLower)(upperLens.map(this, _, _, newUpper ::: _))
+      val current2 = (current1 /: newUpper)(lowerLens.map(this, _, _, newLower ::: _))
+      current2
+    }
+
+  def addLess(param1: PolyParam, param2: PolyParam)(implicit ctx: Context): This =
+    order(this, param1, param2)
+
+  def updateEntry(current: This, param: PolyParam, tp: Type)(implicit ctx: Context): This = {
+    var current1 = boundsLens.update(this, current, param, tp)
+    tp match {
+      case TypeBounds(lo, hi) =>
+        for (p <- dependentParams(lo, isUpper = false))
+          current1 = order(current1, p, param)
+        for (p <- dependentParams(hi, isUpper = true))
+          current1 = order(current1, param, p)
+      case _ =>
+    }
+    current1
+  }
+
+  def updateEntry(param: PolyParam, tp: Type)(implicit ctx: Context): This =
+    updateEntry(this, param, tp)
+
+  def unify(p1: PolyParam, p2: PolyParam)(implicit ctx: Context): This = {
+    val p1Bounds = (nonParamBounds(p1) & nonParamBounds(p2)).substParam(p2, p1)
+    updateEntry(p1, p1Bounds).replace(p2, p1)
+  }
+
+  def narrowBound(param: PolyParam, bound: Type, isUpper: Boolean)(implicit ctx: Context): This = {
+    val oldBounds @ TypeBounds(lo, hi) = nonParamBounds(param)
+    val newBounds =
+      if (isUpper) oldBounds.derivedTypeBounds(lo, hi & bound)
+      else oldBounds.derivedTypeBounds(lo | bound, hi)
+    updateEntry(param, newBounds)
+  }
+
+// ---------- Removals ------------------------------------------------------------
+
+  /** A new constraint which is derived from this constraint by removing
+   *  the type parameter `param` from the domain and replacing all top-level occurrences
+   *  of the parameter elsewhere in the constraint by type `tp`, or a conservative
+   *  approximation of it if that is needed to avoid cycles.
+   *  Occurrences nested inside a refinement or prefix are not affected.
+   *
+   *  The reason we need to substitute top-level occurrences of the parameter
+   *  is to deal with situations like the following. Say we have in the constraint
+   *
+   *      P <: Q & String
+   *      Q
+   *
+   *  and we replace Q with P. Then substitution gives
+   *
+   *      P <: P & String
+   *
+   *  this would be a cyclic constraint is therefore changed by `normalize` and
+   *  `recombine` below to
+   *
+   *      P <: String
+   *
+   *  approximating the RHS occurrence of P with Any. Without the substitution we
+   *  would not find out where we need to approximate. Occurrences of parameters
+   *  that are not top-level are not affected.
+   */
+  def replace(param: PolyParam, tp: Type)(implicit ctx: Context): OrderingConstraint = {
+    val replacement = tp.dealias.stripTypeVar
+    if (param == replacement) this
+    else {
+      assert(replacement.isValueTypeOrLambda)
+      val poly = param.binder
+      val idx = param.paramNum
+
+      def removeParam(ps: List[PolyParam]) =
+        ps.filterNot(p => p.binder.eq(poly) && p.paramNum == idx)
+
+      def replaceParam(tp: Type, atPoly: PolyType, atIdx: Int): Type = tp match {
+        case bounds @ TypeBounds(lo, hi) =>
+
+          def recombine(andor: AndOrType, op: (Type, Boolean) => Type, isUpper: Boolean): Type = {
+            val tp1 = op(andor.tp1, isUpper)
+            val tp2 = op(andor.tp2, isUpper)
+            if ((tp1 eq andor.tp1) && (tp2 eq andor.tp2)) andor
+            else if (andor.isAnd) tp1 & tp2
+            else tp1 | tp2
+          }
+
+          def normalize(tp: Type, isUpper: Boolean): Type = tp match {
+            case p: PolyParam if p.binder == atPoly && p.paramNum == atIdx =>
+              if (isUpper) defn.AnyType else defn.NothingType
+            case tp: AndOrType if isUpper == tp.isAnd => recombine(tp, normalize, isUpper)
+            case _ => tp
+          }
+
+          def replaceIn(tp: Type, isUpper: Boolean): Type = tp match {
+            case `param` => normalize(replacement, isUpper)
+            case tp: AndOrType if isUpper == tp.isAnd => recombine(tp, replaceIn, isUpper)
+            case _ => tp.substParam(param, replacement)
+          }
+
+          bounds.derivedTypeBounds(replaceIn(lo, isUpper = false), replaceIn(hi, isUpper = true))
+        case _ =>
+          tp.substParam(param, replacement)
+      }
+
+      var current =
+        if (isRemovable(poly)) remove(poly) else updateEntry(param, replacement)
+      current.foreachParam {(p, i) =>
+        current = boundsLens.map(this, current, p, i, replaceParam(_, p, i))
+        current = lowerLens.map(this, current, p, i, removeParam)
+        current = upperLens.map(this, current, p, i, removeParam)
+      }
+      current
+    }
+  }
+
+  def remove(pt: PolyType)(implicit ctx: Context): This = {
+    def removeFromOrdering(po: ParamOrdering) = {
+      def removeFromBoundss(key: PolyType, bndss: Array[List[PolyParam]]): Array[List[PolyParam]] = {
+        val bndss1 = bndss.map(_.filterConserve(_.binder ne pt))
+        if (bndss.corresponds(bndss1)(_ eq _)) bndss else bndss1
+      }
+      po.remove(pt).mapValuesNow(removeFromBoundss)
+    }
+    newConstraint(boundsMap.remove(pt), removeFromOrdering(lowerMap), removeFromOrdering(upperMap))
+  }
+
+  def isRemovable(pt: PolyType): Boolean = {
+    val entries = boundsMap(pt)
+    @tailrec def allRemovable(last: Int): Boolean =
+      if (last < 0) true
+      else typeVar(entries, last) match {
+        case tv: TypeVar => tv.inst.exists && allRemovable(last - 1)
+        case _ => false
+      }
+    allRemovable(paramCount(entries) - 1)
+  }
+
+// ---------- Exploration --------------------------------------------------------
+
+  def domainPolys: List[PolyType] = boundsMap.keys
+
+  def domainParams: List[PolyParam] =
+    for {
+      (poly, entries) <- boundsMap.toList
+      n <- 0 until paramCount(entries)
+      if entries(n).exists
+    } yield PolyParam(poly, n)
+
+  def forallParams(p: PolyParam => Boolean): Boolean = {
+    boundsMap.foreachBinding { (poly, entries) =>
+      for (i <- 0 until paramCount(entries))
+        if (isBounds(entries(i)) && !p(PolyParam(poly, i))) return false
+    }
+    true
+  }
+
+  def foreachParam(p: (PolyType, Int) => Unit): Unit =
+    boundsMap.foreachBinding { (poly, entries) =>
+      0.until(poly.paramNames.length).foreach(p(poly, _))
+    }
+
+  def foreachTypeVar(op: TypeVar => Unit): Unit =
+    boundsMap.foreachBinding { (poly, entries) =>
+      for (i <- 0 until paramCount(entries)) {
+        typeVar(entries, i) match {
+          case tv: TypeVar if !tv.inst.exists => op(tv)
+          case _ =>
+        }
+      }
+    }
+
+  def & (other: Constraint)(implicit ctx: Context) = {
+    def merge[T](m1: ArrayValuedMap[T], m2: ArrayValuedMap[T], join: (T, T) => T): ArrayValuedMap[T] = {
+      var merged = m1
+      def mergeArrays(xs1: Array[T], xs2: Array[T]) = {
+        val xs = xs1.clone
+        for (i <- xs.indices) xs(i) = join(xs1(i), xs2(i))
+        xs
+      }
+      m2.foreachBinding { (poly, xs2) =>
+        merged = merged.updated(poly,
+            if (m1.contains(poly)) mergeArrays(m1(poly), xs2) else xs2)
+      }
+      merged
+    }
+
+    def mergeParams(ps1: List[PolyParam], ps2: List[PolyParam]) =
+      (ps1 /: ps2)((ps1, p2) => if (ps1.contains(p2)) ps1 else p2 :: ps1)
+
+    def mergeEntries(e1: Type, e2: Type): Type = e1 match {
+        case e1: TypeBounds =>
+          e2 match {
+            case e2: TypeBounds => e1 & e2
+            case _ if e1 contains e2 => e2
+            case _ => mergeError
+          }
+        case tv1: TypeVar =>
+          e2 match {
+            case tv2: TypeVar if tv1.instanceOpt eq tv2.instanceOpt => e1
+            case _ => mergeError
+          }
+        case _ if e1 eq e2 => e1
+        case _ => mergeError
+    }
+
+    def mergeError = throw new AssertionError(i"cannot merge $this with $other")
+
+    val that = other.asInstanceOf[OrderingConstraint]
+    new OrderingConstraint(
+        merge(this.boundsMap, that.boundsMap, mergeEntries),
+        merge(this.lowerMap, that.lowerMap, mergeParams),
+        merge(this.upperMap, that.upperMap, mergeParams))
+  }
+
+  override def checkClosed()(implicit ctx: Context): Unit = {
+    def isFreePolyParam(tp: Type) = tp match {
+      case PolyParam(binder: PolyType, _) => !contains(binder)
+      case _ => false
+    }
+    def checkClosedType(tp: Type, where: String) =
+      if (tp != null)
+        assert(!tp.existsPart(isFreePolyParam), i"unclosed constraint: $this refers to $tp in $where")
+    boundsMap.foreachBinding((_, tps) => tps.foreach(checkClosedType(_, "bounds")))
+    lowerMap.foreachBinding((_, paramss) => paramss.foreach(_.foreach(checkClosedType(_, "lower"))))
+    upperMap.foreachBinding((_, paramss) => paramss.foreach(_.foreach(checkClosedType(_, "upper"))))
+  }
+
+  private var myUninstVars: mutable.ArrayBuffer[TypeVar] = _
+
+  /** The uninstantiated typevars of this constraint */
+  def uninstVars: collection.Seq[TypeVar] = {
+    if (myUninstVars == null) {
+      myUninstVars = new mutable.ArrayBuffer[TypeVar]
+      boundsMap.foreachBinding { (poly, entries) =>
+        for (i <- 0 until paramCount(entries)) {
+          typeVar(entries, i) match {
+            case tv: TypeVar if !tv.inst.exists && isBounds(entries(i)) => myUninstVars += tv
+            case _ =>
+          }
+        }
+      }
+    }
+    myUninstVars
+  }
+
+// ---------- Cyclic checking -------------------------------------------
+
+  def checkNonCyclic()(implicit ctx: Context): Unit =
+    domainParams.foreach(checkNonCyclic)
+
+  private def checkNonCyclic(param: PolyParam)(implicit ctx: Context): Unit =
+    assert(!isLess(param, param), i"cyclic constraint involving $param in $this")
+
+// ---------- toText -----------------------------------------------------
+
+  override def toText(printer: Printer): Text = {
+    def entryText(tp: Type) = tp match {
+      case tp: TypeBounds =>
+        tp.toText(printer)
+      case _ =>
+        " := " ~ tp.toText(printer)
+    }
+    val indent = 3
+    val header: Text = "Constraint("
+    val uninstVarsText = " uninstVars = " ~
+      Text(uninstVars map (_.toText(printer)), ", ") ~ ";"
+    val constrainedText =
+      " constrained types = " ~ Text(domainPolys map (_.toText(printer)), ", ")
+    val boundsText =
+      " bounds = " ~ {
+        val assocs =
+          for (param <- domainParams)
+          yield (" " * indent) ~ param.toText(printer) ~ entryText(entry(param))
+        Text(assocs, "\n")
+      }
+    val orderingText =
+      " ordering = " ~ {
+        val deps =
+          for {
+            param <- domainParams
+            ups = minUpper(param)
+            if ups.nonEmpty
+          }
+          yield
+            (" " * indent) ~ param.toText(printer) ~ " <: " ~
+              Text(ups.map(_.toText(printer)), ", ")
+        Text(deps, "\n")
+      }
+    Text.lines(List(header, uninstVarsText, constrainedText, boundsText, orderingText, ")"))
+  }
+
+  override def toString: String = {
+    def entryText(tp: Type): String = tp match {
+      case tp: TypeBounds => tp.toString
+      case _ =>" := " + tp
+    }
+    val constrainedText =
+      " constrained types = " + domainPolys.mkString("\n")
+    val boundsText =
+      " bounds = " + {
+        val assocs =
+          for (param <- domainParams)
+          yield
+            param.binder.paramNames(param.paramNum) + ": " + entryText(entry(param))
+        assocs.mkString("\n")
+    }
+    constrainedText + "\n" + boundsText
+  }
+}