From cdfbdb14f0d6bb4f3a5dd284fd17e86addaa5d03 Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Thu, 18 Feb 2016 10:29:41 +0100
Subject: [PATCH] Keep named arguments during eta expansion

Fixes #1096.
---
 src/dotty/tools/dotc/typer/EtaExpansion.scala | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/src/dotty/tools/dotc/typer/EtaExpansion.scala b/src/dotty/tools/dotc/typer/EtaExpansion.scala
index aa210e6ed40a..f4a1f97cd74f 100644
--- a/src/dotty/tools/dotc/typer/EtaExpansion.scala
+++ b/src/dotty/tools/dotc/typer/EtaExpansion.scala
@@ -48,13 +48,11 @@ object EtaExpansion {
   }
 
   /** Lift a function argument, stripping any NamedArg wrapper */
-  def liftArg(defs: mutable.ListBuffer[Tree], arg: Tree, prefix: String = "")(implicit ctx: Context): Tree = {
-    val arg1 = arg match {
-      case NamedArg(_, arg1) => arg1
-      case arg => arg
+  def liftArg(defs: mutable.ListBuffer[Tree], arg: Tree, prefix: String = "")(implicit ctx: Context): Tree =
+    arg match {
+      case arg @ NamedArg(name, arg1) => cpy.NamedArg(arg)(name, lift(defs, arg1, prefix))
+      case arg => lift(defs, arg, prefix)
     }
-    lift(defs, arg1, prefix)
-  }
 
   /** Lift arguments that are not-idempotent into ValDefs in buffer `defs`
    *  and replace by the idents of so created ValDefs.