Fix ordering problem for applications

In an application with named and default arguments, where arguments
have side effects and are given out of order, and some arguments are
missing, the previous algorithm worked only if typed and untyped argument
trees were the same.

Test i2916 started failing once literals were represented as Number trees,
since then untyped and typed versions of the argument were different.

Author: odersky

compiler/src/dotty/tools/dotc/typer/Applications.scala

@@ -758,23 +758,27 @@ trait Applications extends Compatibility {
             // lift arguments in the definition order
             val argDefBuf = mutable.ListBuffer.empty[Tree]
             typedArgs = lifter.liftArgs(argDefBuf, methType, typedArgs)
-
             // Lifted arguments ordered based on the original order of typedArgBuf and
             // with all non-explicit default parameters at the end in declaration order.
             val orderedArgDefs = {
-              // List of original arguments that are lifted by liftArgs
-              val impureArgs = typedArgBuf.filterNot(lifter.noLift)
-              // Assuming stable sorting all non-explicit default parameters will remain in the end with the same order
-              val defaultParamIndex = args.size
-              // Mapping of index of each `liftable` into original args ordering
-              val indices = impureArgs.map { arg =>
-                val idx = args.indexOf(arg)
-                if (idx >= 0) idx // original index skipping pure arguments
-                else defaultParamIndex
+              // Indices of original typed arguments that are lifted by liftArgs
+              val impureArgIndices = typedArgBuf.zipWithIndex.collect {
+                case (arg, idx) if !lifter.noLift(arg) => idx
+              }
+              def position(arg: Trees.Tree[T]) = {
+                val i = args.indexOf(arg)
+                if (i >= 0) i else orderedArgs.length
               }
-              scala.util.Sorting.stableSort[(Tree, Int), Int](argDefBuf zip indices, x => x._2).map(_._1)
+              // The original indices of all ordered arguments, as an array
+              val originalIndices = orderedArgs.map(position).toArray
+              // Assuming stable sorting all non-explicit default parameters will remain in the end with the same order
+              val defaultParamIndex = typedArgs.size
+              // A map from lifted argument index to the corresponding position in the original argument list
+              def originalIndex(n: Int) =
+                if (n < originalIndices.length) originalIndices(n) else orderedArgs.length
+              scala.util.Sorting.stableSort[(Tree, Int), Int](
+                argDefBuf.zip(impureArgIndices), (arg, idx) => originalIndex(idx)).map(_._1)
             }
-
             liftedDefs ++= orderedArgDefs
           }
           if (sameSeq(typedArgs, args)) // trick to cut down on tree copying