Fix eta expansion for deeply curried methods

Eta expansion yielded incorrect result if the eta expanded method
has more than one parameter sections and the expected result type
is a unary function type. In that case a postfix `_' needs to be appended.

Author: odersky

src/dotty/tools/dotc/typer/EtaExpansion.scala

@@ -142,7 +142,11 @@ object EtaExpansion {
     var ids: List[Tree] = mt.paramNames map (name => Ident(name).withPos(tree.pos))
     if (mt.paramTypes.nonEmpty && mt.paramTypes.last.isRepeatedParam)
       ids = ids.init :+ repeated(ids.last)
-    val body = Apply(lifted, ids)
+    var body: Tree = Apply(lifted, ids)
+    mt.resultType match {
+      case rt: MethodType if !rt.isImplicit => body = PostfixOp(body, nme.WILDCARD)
+      case _ =>
+    }
     val fn = untpd.Function(params, body)
     if (defs.nonEmpty) untpd.Block(defs.toList map untpd.TypedSplice, fn) else fn
   }

tests/pending/run/tcpoly_parseridioms.check

@@ -108,5 +108,5 @@ trait ParserIdioms extends Parsers with Idioms {
 }
 
 object Test extends ParserIdioms with App {
-  println(expr("12".toList))
+  assert(expr("12".toList).toString == "Success(List(),Plus(1,2))")
 }