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-rw-r--r--src/reflect/scala/reflect/internal/Types.scala127
-rw-r--r--test/files/neg/lubs.check9
-rw-r--r--test/files/pos/ticket2251.scala14
-rw-r--r--test/files/run/lub-visibility.check2
-rw-r--r--test/files/run/t2251.check1
-rw-r--r--test/files/run/t2251.scala19
-rw-r--r--test/files/run/t2251b.check11
-rw-r--r--test/files/run/t2251b.scala48
8 files changed, 178 insertions, 53 deletions
diff --git a/src/reflect/scala/reflect/internal/Types.scala b/src/reflect/scala/reflect/internal/Types.scala
index 7df34a14e2..f519a2d4a6 100644
--- a/src/reflect/scala/reflect/internal/Types.scala
+++ b/src/reflect/scala/reflect/internal/Types.scala
@@ -6219,25 +6219,26 @@ trait Types extends api.Types { self: SymbolTable =>
* @See baseTypeSeq for a definition of sorted and upwards closed.
*/
private def lubList(ts: List[Type], depth: Int): List[Type] = {
- // Matching the type params of one of the initial types means dummies.
- val initialTypeParams = ts map (_.typeParams)
- def isHotForTs(xs: List[Type]) = initialTypeParams contains xs.map(_.typeSymbol)
-
+ var lubListDepth = 0
+ // This catches some recursive situations which would otherwise
+ // befuddle us, e.g. pos/hklub0.scala
+ def isHotForTs(xs: List[Type]) = ts exists (_.typeParams == xs.map(_.typeSymbol))
def elimHigherOrderTypeParam(tp: Type) = tp match {
- case TypeRef(pre, sym, args) if args.nonEmpty && isHotForTs(args) => tp.typeConstructor
- case _ => tp
+ case TypeRef(_, _, args) if args.nonEmpty && isHotForTs(args) =>
+ logResult("Retracting dummies from " + tp + " in lublist")(tp.typeConstructor)
+ case _ => tp
}
- var lubListDepth = 0
- def loop(tsBts: List[List[Type]]): List[Type] = {
+ // pretypes is a tail-recursion-preserving accumulator.
+ @annotation.tailrec def loop(pretypes: List[Type], tsBts: List[List[Type]]): List[Type] = {
lubListDepth += 1
- if (tsBts.isEmpty || tsBts.exists(_.isEmpty)) Nil
- else if (tsBts.tail.isEmpty) tsBts.head
+ if (tsBts.isEmpty || tsBts.exists(_.isEmpty)) pretypes.reverse
+ else if (tsBts.tail.isEmpty) pretypes.reverse ++ tsBts.head
else {
// ts0 is the 1-dimensional frontier of symbols cutting through 2-dimensional tsBts.
// Invariant: all symbols "under" (closer to the first row) the frontier
// are smaller (according to _.isLess) than the ones "on and beyond" the frontier
- val ts0 = tsBts map (_.head)
+ val ts0 = tsBts map (_.head)
// Is the frontier made up of types with the same symbol?
val isUniformFrontier = (ts0: @unchecked) match {
@@ -6250,23 +6251,23 @@ trait Types extends api.Types { self: SymbolTable =>
// merging, strip targs that refer to bound tparams (when we're computing the lub of type
// constructors.) Also filter out all types that are a subtype of some other type.
if (isUniformFrontier) {
- if (settings.debug.value || printLubs) {
- val fbounds = findRecursiveBounds(ts0)
- if (fbounds.nonEmpty) {
- println("Encountered " + fbounds.size + " recursive bounds while lubbing " + ts0.size + " types.")
- for ((p0, p1) <- fbounds) {
- val desc = if (p0 == p1) "its own bounds" else "the bounds of " + p1
-
- println(" " + p0.fullLocationString + " appears in " + desc)
- println(" " + p1 + " " + p1.info.bounds)
+ val fbounds = findRecursiveBounds(ts0) map (_._2)
+ val tcLubList = typeConstructorLubList(ts0)
+ def isRecursive(tp: Type) = tp.typeSymbol.typeParams exists fbounds.contains
+
+ val ts1 = ts0 map { t =>
+ if (isRecursive(t)) {
+ tcLubList map (t baseType _.typeSymbol) find (t => !isRecursive(t)) match {
+ case Some(tp) => logResult(s"Breaking recursion in lublist, substituting weaker type.\n Was: $t\n Now")(tp)
+ case _ => t
}
- println("")
}
+ else t
}
val tails = tsBts map (_.tail)
- mergePrefixAndArgs(elimSub(ts0 map elimHigherOrderTypeParam, depth), 1, depth) match {
- case Some(tp) => tp :: loop(tails)
- case _ => loop(tails)
+ mergePrefixAndArgs(elimSub(ts1, depth) map elimHigherOrderTypeParam, 1, depth) match {
+ case Some(tp) => loop(tp :: pretypes, tails)
+ case _ => loop(pretypes, tails)
}
}
else {
@@ -6283,7 +6284,7 @@ trait Types extends api.Types { self: SymbolTable =>
printLubMatrix((ts zip tsBts).toMap, lubListDepth)
}
- loop(newtps)
+ loop(pretypes, newtps)
}
}
}
@@ -6292,7 +6293,7 @@ trait Types extends api.Types { self: SymbolTable =>
if (printLubs)
printLubMatrix((ts zip initialBTSes).toMap, depth)
- loop(initialBTSes)
+ loop(Nil, initialBTSes)
}
/** The minimal symbol (wrt Symbol.isLess) of a list of types */
@@ -6427,6 +6428,23 @@ trait Types extends api.Types { self: SymbolTable =>
private val lubResults = new mutable.HashMap[(Int, List[Type]), Type]
private val glbResults = new mutable.HashMap[(Int, List[Type]), Type]
+ /** Given a list of types, finds all the base classes they have in
+ * common, then returns a list of type constructors derived directly
+ * from the symbols (so any more specific type information is ignored.)
+ * The list is filtered such that every type constructor in the list
+ * expects the same number of type arguments, which is chosen based
+ * on the deepest class among the common baseclasses.
+ */
+ def typeConstructorLubList(ts: List[Type]): List[Type] = {
+ val bcs = ts.flatMap(_.baseClasses).distinct sortWith (_ isLess _)
+ val tcons = bcs filter (clazz => ts forall (_.typeSymbol isSubClass clazz))
+
+ tcons map (_.typeConstructor) match {
+ case Nil => Nil
+ case t :: ts => t :: ts.filter(_.typeParams.size == t.typeParams.size)
+ }
+ }
+
def lub(ts: List[Type]): Type = ts match {
case List() => NothingClass.tpe
case List(t) => t
@@ -6434,8 +6452,20 @@ trait Types extends api.Types { self: SymbolTable =>
Statistics.incCounter(lubCount)
val start = Statistics.pushTimer(typeOpsStack, lubNanos)
try {
- lub(ts, lubDepth(ts))
- } finally {
+ val res = lub(ts, lubDepth(ts))
+ // If the number of unapplied type parameters in all incoming
+ // types is consistent, and the lub does not match that, return
+ // the type constructor of the calculated lub instead. This
+ // is because lubbing type constructors tends to result in types
+ // which have been applied to dummies or Nothing.
+ ts.map(_.typeParams.size).distinct match {
+ case x :: Nil if res.typeParams.size != x =>
+ logResult(s"Stripping type args from lub because $res is not consistent with $ts")(res.typeConstructor)
+ case _ =>
+ res
+ }
+ }
+ finally {
lubResults.clear()
glbResults.clear()
Statistics.popTimer(typeOpsStack, start)
@@ -6469,13 +6499,13 @@ trait Types extends api.Types { self: SymbolTable =>
}
}
def lub1(ts0: List[Type]): Type = {
- val (ts, tparams) = stripExistentialsAndTypeVars(ts0)
+ val (ts, tparams) = stripExistentialsAndTypeVars(ts0)
val lubBaseTypes: List[Type] = lubList(ts, depth)
- val lubParents = spanningTypes(lubBaseTypes)
- val lubOwner = commonOwner(ts)
- val lubBase = intersectionType(lubParents, lubOwner)
+ val lubParents = spanningTypes(lubBaseTypes)
+ val lubOwner = commonOwner(ts)
+ val lubBase = intersectionType(lubParents, lubOwner)
val lubType =
- if (phase.erasedTypes || depth == 0) lubBase
+ if (phase.erasedTypes || depth == 0 ) lubBase
else {
val lubRefined = refinedType(lubParents, lubOwner)
val lubThisType = lubRefined.typeSymbol.thisType
@@ -6492,6 +6522,7 @@ trait Types extends api.Types { self: SymbolTable =>
val syms = narrowts map (t =>
t.nonPrivateMember(proto.name).suchThat(sym =>
sym.tpe matches prototp.substThis(lubThisType.typeSymbol, t)))
+
if (syms contains NoSymbol) NoSymbol
else {
val symtypes =
@@ -6518,10 +6549,8 @@ trait Types extends api.Types { self: SymbolTable =>
// add a refinement symbol for all non-class members of lubBase
// which are refined by every type in ts.
for (sym <- lubBase.nonPrivateMembers ; if !excludeFromLub(sym)) {
- try {
- val lsym = lubsym(sym)
- if (lsym != NoSymbol) addMember(lubThisType, lubRefined, lsym, depth)
- } catch {
+ try lubsym(sym) andAlso (addMember(lubThisType, lubRefined, _, depth))
+ catch {
case ex: NoCommonType =>
}
}
@@ -6765,18 +6794,16 @@ trait Types extends api.Types { self: SymbolTable =>
debuglog("transposed irregular matrix!?" +(tps, argss))
None
case Some(argsst) =>
- val args = map2(sym.typeParams, argsst) { (tparam, as) =>
- if (depth == 0) {
- if (tparam.variance == variance) {
- // Take the intersection of the upper bounds of the type parameters
- // rather than falling all the way back to "Any", otherwise we end up not
- // conforming to bounds.
- val bounds0 = sym.typeParams map (_.info.bounds.hi) filterNot (_.typeSymbol == AnyClass)
- if (bounds0.isEmpty) AnyClass.tpe
- else intersectionType(bounds0 map (b => b.asSeenFrom(tps.head, sym)))
- }
- else if (tparam.variance == -variance) NothingClass.tpe
- else NoType
+ val args = map2(sym.typeParams, argsst) { (tparam, as0) =>
+ val as = as0.distinct
+ if (as.size == 1) as.head
+ else if (depth == 0) {
+ log("Giving up merging args: can't unify %s under %s".format(as.mkString(", "), tparam.fullLocationString))
+ // Don't return "Any" (or "Nothing") when we have to give up due to
+ // recursion depth. Return NoType, which prevents us from poisoning
+ // lublist's results. It can recognize the recursion and deal with it, but
+ // only if we aren't returning invalid types.
+ NoType
}
else {
if (tparam.variance == variance) lub(as, decr(depth))
@@ -6785,7 +6812,7 @@ trait Types extends api.Types { self: SymbolTable =>
val l = lub(as, decr(depth))
val g = glb(as, decr(depth))
if (l <:< g) l
- else { // Martin: I removed this, because incomplete. Not sure there is a good way to fix it. For the moment we
+ else { // Martin: I removed this, because incomplete. Not sure there is a good way to fix it. For the moment we
// just err on the conservative side, i.e. with a bound that is too high.
// if(!(tparam.info.bounds contains tparam)) //@M can't deal with f-bounds, see #2251
diff --git a/test/files/neg/lubs.check b/test/files/neg/lubs.check
index 77ab20102c..affbd4983c 100644
--- a/test/files/neg/lubs.check
+++ b/test/files/neg/lubs.check
@@ -1,5 +1,10 @@
+lubs.scala:10: error: type mismatch;
+ found : test1.A[test1.A[Object]]
+ required: test1.A[test1.A[test1.A[Any]]]
+ val x3: A[A[A[Any]]] = f
+ ^
lubs.scala:11: error: type mismatch;
- found : test1.A[test1.A[test1.A[Any]]]
+ found : test1.A[test1.A[Object]]
required: test1.A[test1.A[test1.A[test1.A[Any]]]]
val x4: A[A[A[A[Any]]]] = f
^
@@ -13,4 +18,4 @@ lubs.scala:25: error: type mismatch;
required: test2.A{type T >: Null <: test2.A{type T >: Null <: test2.A{type T >: Null <: test2.A}}}
val x4: A { type T >: Null <: A { type T >: Null <: A { type T >: Null <: A } } } = f
^
-three errors found
+four errors found
diff --git a/test/files/pos/ticket2251.scala b/test/files/pos/ticket2251.scala
index b3afee4ea9..c220e85350 100644
--- a/test/files/pos/ticket2251.scala
+++ b/test/files/pos/ticket2251.scala
@@ -22,4 +22,18 @@ lub of List(D, C) is B[_2] forSome { type _2 >: D with C{} <: B[_1] forSome { ty
// should be: B[X] forSome {type X <: B[X]} -- can this be done automatically? for now, just detect f-bounded polymorphism and fall back to more coarse approximation
val data: List[A] = List(new C, new D)
+
+ val data2 = List(new C, new D)
+
+ val data3: List[B[X] forSome { type X <: B[_ <: A] }] = List(new C, new D)
+
+ // Not yet --
+ // val data4: List[B[X] forSome { type X <: B[X] }] = List(new C, new D)
+ // <console>:7: error: type mismatch;
+ // found : List[B[_ >: D with C <: B[_ >: D with C <: A]]]
+ // required: List[B[X] forSome { type X <: B[X] }]
+ // val data4: List[B[X] forSome { type X <: B[X] }] = List(new C, new D)
+
+ // works
+ val data5 = List[B[X] forSome { type X <: B[X] }](new C, new D)
}
diff --git a/test/files/run/lub-visibility.check b/test/files/run/lub-visibility.check
index 3461d1bf6b..f3a6bef215 100644
--- a/test/files/run/lub-visibility.check
+++ b/test/files/run/lub-visibility.check
@@ -8,7 +8,7 @@ scala> // should infer List[scala.collection.immutable.Seq[Nothing]]
scala> // but reverted that for SI-5534.
scala> val x = List(List(), Vector())
-x: List[scala.collection.immutable.Seq[Nothing] with scala.collection.AbstractSeq[Nothing]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.Seq with scala.collection.AbstractSeq{def dropRight(n: Int): scala.collection.immutable.Seq[Any] with scala.collection.AbstractSeq[Any]; def takeRight(n: Int): scala.collection.immutable.Seq[Any] with scala.collection.AbstractSeq[Any]; def drop(n: Int): scala.collection.immutable.Seq[Any] with scala.collection.AbstractSeq[Any]; def take(n: Int): scala.collection.immutable.Seq[Any] with scala.collection.AbstractSeq[Any]; def slice(from: Int,until: Int): scala.collection.immutable.Seq[Any] with scala.collection.AbstractSeq[Any]}]; def dropRight(n: Int): scala.collection.immutable.Seq[Nothing] with scala.collection.Ab...
+x: List[scala.collection.immutable.Seq[Nothing] with scala.collection.AbstractSeq[Nothing]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.Seq with scala.collection.AbstractSeq]; def dropRight(n: Int): scala.collection.immutable.Seq[Nothing] with scala.collection.AbstractSeq[Nothing]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.Seq with scala.collection.AbstractSeq]; def dropRight(n: Int): scala.collection.immutable.Seq[Nothing] with scala.collection.AbstractSeq[Nothing]{def dropRight(n: Int): scala.collection.immutable.Seq[Nothing] with scala.collection.AbstractSeq[Nothing]; def takeRight(n: Int): scala.collection.immutable.Seq[Nothing] with scala.collection.AbstractSeq[Nothing]; def drop(n: Int): scala.collecti...
scala>
scala>
diff --git a/test/files/run/t2251.check b/test/files/run/t2251.check
new file mode 100644
index 0000000000..55ad2a5857
--- /dev/null
+++ b/test/files/run/t2251.check
@@ -0,0 +1 @@
+Set(List(List(C), Stream(D, ?)))
diff --git a/test/files/run/t2251.scala b/test/files/run/t2251.scala
new file mode 100644
index 0000000000..00c5619b49
--- /dev/null
+++ b/test/files/run/t2251.scala
@@ -0,0 +1,19 @@
+class A
+trait B[T <: B[T]] extends A
+class C extends B[C] { override def toString = "C" }
+class D extends B[D] { override def toString = "D" }
+
+class E {
+ val ys = List(List(new C), Stream(new D))
+}
+
+object Test {
+ def trav = List(List(), Stream())
+
+ def main(args: Array[String]): Unit = {
+ val f = (new E).ys _
+ var xs: Set[List[_ <: Seq[B[_]]]] = Set()
+ xs += f()
+ println(xs)
+ }
+}
diff --git a/test/files/run/t2251b.check b/test/files/run/t2251b.check
new file mode 100644
index 0000000000..42b0be457a
--- /dev/null
+++ b/test/files/run/t2251b.check
@@ -0,0 +1,11 @@
+TypeTag[List[scala.collection.immutable.LinearSeq[B[_ >: D with C <: B[_ >: D with C <: A]]] with scala.collection.AbstractSeq[B[_ >: D with C <: B[_ >: D with C <: A]]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.LinearSeq with scala.collection.AbstractSeq]; def reverse: scala.collection.immutable.LinearSeq[B[_ >: D with C <: A]] with scala.collection.AbstractSeq[B[_ >: D with C <: A]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.LinearSeq with scala.collection.AbstractSeq]; def reverse: scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def dropRight(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def takeRight(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def drop(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def take(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def slice(from: Int,until: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]}; def dropRight(n: Int): scala.collection.immutable.LinearSeq[B[_ >: D with C <: A]] with scala.collection.AbstractSeq[B[_ >: D with C <: A]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.LinearSeq with scala.collection.AbstractSeq]; def reverse: scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def dropRight(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def takeRight(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def drop(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def take(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def slice(from: Int,until: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]}; def takeRight(n: Int): scala.collection.immutable.LinearSeq[B[_ >: D with C <: A]] with scala.collection.AbstractSeq[B[_ >: D with C <: A]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.LinearSeq with scala.collection.AbstractSeq]; def reverse: scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def dropRight(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def takeRight(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def drop(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def take(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def slice(from: Int,until: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]}; def drop(n: Int): scala.collection.immutable.LinearSeq[B[_ >: D with C <: A]] with scala.collection.AbstractSeq[B[_ >: D with C <: A]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.LinearSeq with scala.collection.AbstractSeq]; def reverse: scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def dropRight(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def takeRight(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def drop(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def take(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def slice(from: Int,until: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]}; def take(n: Int): scala.collection.immutable.LinearSeq[B[_ >: D with C <: A]] with scala.collection.AbstractSeq[B[_ >: D with C <: A]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.LinearSeq with scala.collection.AbstractSeq]; def reverse: scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def dropRight(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def takeRight(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def drop(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def take(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def slice(from: Int,until: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]}; def slice(from: Int,until: Int): scala.collection.immutable.LinearSeq[B[_ >: D with C <: A]] with scala.collection.AbstractSeq[B[_ >: D with C <: A]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.LinearSeq with scala.collection.AbstractSeq]; def reverse: scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def dropRight(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def takeRight(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def drop(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def take(n: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]; def slice(from: Int,until: Int): scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A]}; def splitAt(n: Int): (scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A], scala.collection.immutable.LinearSeq[A] with scala.collection.AbstractSeq[A])}]]
+TypeTag[List[scala.collection.immutable.Iterable[B[_ >: F with E with D with C <: B[_ >: F with E with D with C <: A]]] with F with Int => Any]]
+TypeTag[List[scala.collection.immutable.Seq[B[_ >: D with C <: B[_ >: D with C <: A]]] with scala.collection.AbstractSeq[B[_ >: D with C <: B[_ >: D with C <: A]]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.Seq with scala.collection.AbstractSeq]; def dropRight(n: Int): scala.collection.immutable.Seq[B[_ >: D with C <: A]] with scala.collection.AbstractSeq[B[_ >: D with C <: A]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.Seq with scala.collection.AbstractSeq]; def dropRight(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def takeRight(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def drop(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def take(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def slice(from: Int,until: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def init: scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]}; def takeRight(n: Int): scala.collection.immutable.Seq[B[_ >: D with C <: A]] with scala.collection.AbstractSeq[B[_ >: D with C <: A]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.Seq with scala.collection.AbstractSeq]; def dropRight(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def takeRight(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def drop(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def take(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def slice(from: Int,until: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def init: scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]}; def drop(n: Int): scala.collection.immutable.Seq[B[_ >: D with C <: A]] with scala.collection.AbstractSeq[B[_ >: D with C <: A]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.Seq with scala.collection.AbstractSeq]; def dropRight(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def takeRight(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def drop(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def take(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def slice(from: Int,until: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def init: scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]}; def take(n: Int): scala.collection.immutable.Seq[B[_ >: D with C <: A]] with scala.collection.AbstractSeq[B[_ >: D with C <: A]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.Seq with scala.collection.AbstractSeq]; def dropRight(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def takeRight(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def drop(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def take(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def slice(from: Int,until: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def init: scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]}; def slice(from: Int,until: Int): scala.collection.immutable.Seq[B[_ >: D with C <: A]] with scala.collection.AbstractSeq[B[_ >: D with C <: A]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.Seq with scala.collection.AbstractSeq]; def dropRight(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def takeRight(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def drop(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def take(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def slice(from: Int,until: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def init: scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]}; def splitAt(n: Int): (scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A], scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]); def init: scala.collection.immutable.Seq[B[_ >: D with C <: A]] with scala.collection.AbstractSeq[B[_ >: D with C <: A]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.immutable.Seq with scala.collection.AbstractSeq]; def dropRight(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def takeRight(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def drop(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def take(n: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def slice(from: Int,until: Int): scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]; def init: scala.collection.immutable.Seq[A] with scala.collection.AbstractSeq[A]}}]]
+TypeTag[List[scala.collection.Set[_ >: G with F <: B[_ >: G with F <: B[_ >: G with F <: A]]]]]
+TypeTag[List[scala.collection.Set[_ >: G with F <: B[_ >: G with F <: B[_ >: G with F <: A]]]]]
+TypeTag[List[scala.collection.Set[_ >: G with F <: B[_ >: G with F <: B[_ >: G with F <: A]]]]]
+TypeTag[List[Seq[B[_ >: G with F <: B[_ >: G with F <: A]]]]]
+TypeTag[List[scala.collection.Map[_ >: F with C <: B[_ >: F with C <: B[_ >: F with C <: A]], B[_ >: G with D <: B[_ >: G with D <: A]]]]]
+TypeTag[List[scala.collection.AbstractSeq[B[_ >: G with F <: B[_ >: G with F <: A]]] with scala.collection.LinearSeq[B[_ >: G with F <: B[_ >: G with F <: A]]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.AbstractSeq with scala.collection.LinearSeq]; def dropRight(n: Int): scala.collection.AbstractSeq[B[_ >: G with F <: A]] with scala.collection.LinearSeq[B[_ >: G with F <: A]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.AbstractSeq with scala.collection.LinearSeq]; def dropRight(n: Int): scala.collection.AbstractSeq[A] with scala.collection.LinearSeq[A]; def drop(n: Int): scala.collection.AbstractSeq[A] with scala.collection.LinearSeq[A]; def take(n: Int): scala.collection.AbstractSeq[A] with scala.collection.LinearSeq[A]; def slice(from: Int,until: Int): scala.collection.AbstractSeq[A] with scala.collection.LinearSeq[A]}; def drop(n: Int): scala.collection.AbstractSeq[B[_ >: G with F <: A]] with scala.collection.LinearSeq[B[_ >: G with F <: A]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.AbstractSeq with scala.collection.LinearSeq]; def dropRight(n: Int): scala.collection.AbstractSeq[A] with scala.collection.LinearSeq[A]; def drop(n: Int): scala.collection.AbstractSeq[A] with scala.collection.LinearSeq[A]; def take(n: Int): scala.collection.AbstractSeq[A] with scala.collection.LinearSeq[A]; def slice(from: Int,until: Int): scala.collection.AbstractSeq[A] with scala.collection.LinearSeq[A]}; def take(n: Int): scala.collection.AbstractSeq[B[_ >: G with F <: A]] with scala.collection.LinearSeq[B[_ >: G with F <: A]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.AbstractSeq with scala.collection.LinearSeq]; def dropRight(n: Int): scala.collection.AbstractSeq[A] with scala.collection.LinearSeq[A]; def drop(n: Int): scala.collection.AbstractSeq[A] with scala.collection.LinearSeq[A]; def take(n: Int): scala.collection.AbstractSeq[A] with scala.collection.LinearSeq[A]; def slice(from: Int,until: Int): scala.collection.AbstractSeq[A] with scala.collection.LinearSeq[A]}; def slice(from: Int,until: Int): scala.collection.AbstractSeq[B[_ >: G with F <: A]] with scala.collection.LinearSeq[B[_ >: G with F <: A]]{def companion: scala.collection.generic.GenericCompanion[scala.collection.AbstractSeq with scala.collection.LinearSeq]; def dropRight(n: Int): scala.collection.AbstractSeq[A] with scala.collection.LinearSeq[A]; def drop(n: Int): scala.collection.AbstractSeq[A] with scala.collection.LinearSeq[A]; def take(n: Int): scala.collection.AbstractSeq[A] with scala.collection.LinearSeq[A]; def slice(from: Int,until: Int): scala.collection.AbstractSeq[A] with scala.collection.LinearSeq[A]}}]]
+TypeTag[List[Seq[B[_ >: G with F <: B[_ >: G with F <: A]]]]]
+TypeTag[List[Seq[B[_ >: G with F <: B[_ >: G with F <: A]]]]]
diff --git a/test/files/run/t2251b.scala b/test/files/run/t2251b.scala
new file mode 100644
index 0000000000..b67b3aec1e
--- /dev/null
+++ b/test/files/run/t2251b.scala
@@ -0,0 +1,48 @@
+class A
+trait B[T <: B[T]] extends A
+class B1[T <: B1[T]] extends B[T]
+class C extends B[C] { override def toString = "C" }
+class D extends B[D] { override def toString = "D" }
+class E extends B[E] { override def toString = "E" }
+class F extends B[F] { override def toString = "F" }
+class G extends B1[G] { override def toString = "G" }
+
+object Test {
+ import scala.collection.{ mutable, immutable }
+ import scala.collection.immutable.{ Vector }
+ import scala.reflect.runtime.universe._
+ def what[T: TypeTag](x: T) = println(typeTag[T])
+
+ def main(args: Array[String]): Unit = {
+ what(List(List(new C), Stream(new D)))
+ what(List(List(new C), Stream(new D), Vector(new E), Set(new F)))
+ what(List(immutable.Vector(new C), Stream(new D)))
+ what(List(collection.Set(new F), mutable.Set(new G)))
+ what(List(collection.Set(new F), immutable.Set(new G)))
+ what(List(mutable.Set(new F), immutable.Set(new G)))
+ what(List(mutable.Seq(new F), immutable.Seq(new G)))
+ what(List(mutable.Map(new C -> new D), immutable.Map(new F -> new G)))
+ what(List(mutable.MutableList(new F), immutable.List(new G)))
+ what(List(mutable.Seq(new F), collection.Seq(new G)))
+ what(List(mutable.LinearSeq(new F), collection.IndexedSeq(new G)))
+ }
+}
+
+
+// class D extends B[D] { override def toString = "D" }
+
+
+// class E {
+// val ys = List(List(new C), Stream(new D))
+// }
+
+// object Test {
+// def trav = List(List(), Stream())
+
+// def main(args: Array[String]): Unit = {
+// val f = (new E).ys _
+// var xs: Set[List[_ <: Seq[B[_]]]] = Set()
+// xs += f()
+// println(xs)
+// }
+// }