Fix #2916: Reorder parameters

Author: nicolasstucki

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

@@ -3,7 +3,7 @@ package dotc
 package typer
 
 import core._
-import ast.{Trees, untpd, tpd, TreeInfo}
+import ast.{TreeInfo, Trees, tpd, untpd}
 import util.Positions._
 import util.Stats.track
 import Trees.Untyped
@@ -24,13 +24,17 @@ import NameKinds.DefaultGetterName
 import ProtoTypes._
 import EtaExpansion._
 import Inferencing._
+
 import collection.mutable
-import config.Printers.{typr, unapp, overload}
+import config.Printers.{overload, typr, unapp}
 import TypeApplications._
+
 import language.implicitConversions
 import reporting.diagnostic.Message
 import Constants.{Constant, IntTag, LongTag}
 
+import scala.collection.mutable.ListBuffer
+
 object Applications {
   import tpd._
 
@@ -611,7 +615,28 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
             liftFun()
             val eqSuffixLength = firstDiff(app.args.reverse, orderedArgs.reverse)
             val (liftable, rest) = typedArgs splitAt (typedArgs.length - eqSuffixLength)
+
+            var indices = ListBuffer.empty[Int]
+            var nextDefaultParamIndex = args.size
+            var prefixShift = 0
+            if (liftedDefs.nonEmpty) {
+              indices += 0
+              prefixShift = 1
+            }
+            for (l <- liftable) {
+              if (!args.contains(l)) {
+                indices += prefixShift + nextDefaultParamIndex
+                nextDefaultParamIndex += 1
+              }
+              else indices += prefixShift + args.indexOf(l)
+            }
+
             typedArgs = liftArgs(liftedDefs, methType, liftable) ++ rest
+
+            assert(liftedDefs.size == indices.size)
+            val newOrder = (liftedDefs zip indices).sortBy(_._2).unzip._1.toList
+            liftedDefs = ListBuffer.empty
+            liftedDefs ++= newOrder
           }
           if (sameSeq(typedArgs, args)) // trick to cut down on tree copying
             typedArgs = args.asInstanceOf[List[Tree]]

tests/run/i2916.check

@@ -0,0 +1,43 @@
+1
+2
+3
+4
+5
+
+1
+2
+3
+4
+5
+
+1
+3
+2
+4
+5
+
+1
+3
+5
+2
+4
+
+1
+3
+4
+2
+5
+
+0
+1
+3
+4
+2
+5
+
+0
+1
+3
+4
+2
+5

tests/run/i2916.scala

@@ -0,0 +1,22 @@
+object Test {
+  def p(x: Int) = { println(x); x }
+  def foo(x1: Int, x2: Int, x3: Int, x4: Int = p(4), x5: Int = p(5)) = 1
+  def main(args: Array[String]) = {
+    foo(p(1), p(2), p(3)) // 1 2 3 4 5
+    println()
+    foo(p(1), x2 = p(2), x3 = p(3)) // 1 2 3 4 5
+    println()
+    foo(p(1), x3 = p(3), x2 = p(2)) // 1 3 2 4 5
+    println()
+    foo(p(1), x3 = p(3), x5 = p(5), x2 = p(2)) // 1 3 5 2 4
+    println()
+    foo(p(1), x3 = p(3), x4 = p(4), x2 = p(2)) // 1 3 4 2 5
+    println()
+
+    def test = { println(0); Test }
+    test.foo(p(1), x3 = p(3), x4 = p(4), x2 = p(2)) // 0 1 3 4 2 5
+    println()
+
+    { println(0); Test }.foo(p(1), x3 = p(3), x4 = p(4), x2 = p(2)) // 0 1 3 4 2 5
+  }
+}