Be more careful reading applied types from Tasty

Same principle as reading from Scala2 pickles applied = in the face
of F-bounded polymorphism we cannot assume that the type
parameters are known when we unpickle a type application.

Author: odersky

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -996,7 +996,12 @@ class TreeUnpickler(reader: TastyReader, nameAtRef: NameRef => TermName, posUnpi
               val refinements = readStats(refineCls, end)(localContext(refineCls))
               RefinedTypeTree(parent, refinements, refineCls)
             case APPLIEDtpt =>
-              AppliedTypeTree(readTpt(), until(end)(readTpt()))
+              // If we do directly a tpd.AppliedType tree we might get a
+              // wrong number of arguments in some scenarios reading F-bounded
+              // types. This came up in #137 of collection strawman.
+              val tycon = readTpt()
+              val args = until(end)(readTpt())
+              untpd.AppliedTypeTree(tycon, args).withType(tycon.tpe.safeAppliedTo(args.tpes))
             case ANDtpt =>
               val tpt1 = readTpt()
               val tpt2 = readTpt()