Fiddling with widenening

Fixing two failures in stdlib having to do with widening. In both
cases, a widenIfUnstable was required. One was widening too much,
the other too little.

Author: odersky

compiler/src/dotty/tools/dotc/transform/ElimByName.scala

@@ -71,7 +71,7 @@ class ElimByName extends MiniPhaseTransform with InfoTransformer { thisTransform
 
     def transformArg(arg: Tree, formal: Type): Tree = formal.dealias match {
       case formalExpr: ExprType =>
-        val argType = arg.tpe.widen
+        val argType = arg.tpe.widenIfUnstable
         val argFun = arg match {
           case Apply(Select(qual, nme.apply), Nil)
           if qual.tpe.derivesFrom(defn.FunctionClass(0)) && isPureExpr(qual) =>

compiler/src/dotty/tools/dotc/transform/LiftTry.scala

@@ -57,7 +57,7 @@ class LiftTry extends MiniPhase with IdentityDenotTransformer { thisTransform =>
         ctx.debuglog(i"lifting tree at ${tree.pos}, current owner = ${ctx.owner}")
         val fn = ctx.newSymbol(
           ctx.owner, ctx.freshName("liftedTree").toTermName, Synthetic | Method,
-          MethodType(Nil, tree.tpe), coord = tree.pos)
+          MethodType(Nil, tree.tpe.widenIfUnstable), coord = tree.pos)
         tree.changeOwnerAfter(ctx.owner, fn, thisTransform)
         Block(DefDef(fn, tree) :: Nil, ref(fn).appliedToNone)
       }

compiler/test/dotc/scala-collections.blacklist

@@ -25,7 +25,7 @@
 
 
 
-## Ycheck failures
+## Ycheck failures, presumably linked to TailCalls
 
 ../scala-scala/src/library/scala/collection/parallel/ParIterableLike.scala
 # -Ycheck:classOf fails
@@ -34,13 +34,9 @@
 # -Ycheck:classOf fails
 
 ../scala-scala/src/library/scala/util/control/TailCalls.scala
-# -Ycheck:classOf failure
+# -Ycheck:classOf fails
 
-../scala-scala/src/library/scala/concurrent/impl/ExecutionContextImpl.scala
-# -Ycheck:arrayConstructors failure
 
-../scala-scala/src/library/scala/concurrent/package.scala
-# -Ycheck:arrayConstructors failure
 
 ## Errors having to do with unavailable APIs or language features:
 

compiler/test/dotc/scala-collections.whitelist

@@ -453,7 +453,7 @@
 ../scala-scala/src/library/scala/collection/script/Message.scala
 ../scala-scala/src/library/scala/collection/script/Scriptable.scala
 
-#../scala-scala/src/library/scala/concurrent/package.scala
+../scala-scala/src/library/scala/concurrent/package.scala
 ../scala-scala/src/library/scala/concurrent/Future.scala
 ../scala-scala/src/library/scala/concurrent/Awaitable.scala
 ../scala-scala/src/library/scala/concurrent/BatchingExecutor.scala
@@ -476,7 +476,7 @@
 ../scala-scala/src/library/scala/concurrent/TaskRunner.scala
 ../scala-scala/src/library/scala/concurrent/ThreadPoolRunner.scala
 ../scala-scala/src/library/scala/concurrent/SyncChannel.scala
-#../scala-scala/src/library/scala/concurrent/impl/ExecutionContextImpl.scala
+../scala-scala/src/library/scala/concurrent/impl/ExecutionContextImpl.scala
 
 ../scala-scala/src/library/scala/collection/parallel/package.scala
 ../scala-scala/src/library/scala/collection/parallel/ParIterable.scala