From 6fb382501f7a63f3227a18396a2af0c862e6ab1c Mon Sep 17 00:00:00 2001
From: Som Snytt <som.snytt@gmail.com>
Date: Wed, 15 Feb 2017 10:33:28 -0800
Subject: SI-10190 Elide string to empty instead of null

Avoid NPE when eliding string-valued functions.

For example, `log(s"$cheap$expensive")` needn't print null.

This is a natural and inexpensive way to elide strings.
---
 src/compiler/scala/tools/nsc/transform/UnCurry.scala | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

(limited to 'src')

diff --git a/src/compiler/scala/tools/nsc/transform/UnCurry.scala b/src/compiler/scala/tools/nsc/transform/UnCurry.scala
index 096b6b9263..c3006a4786 100644
--- a/src/compiler/scala/tools/nsc/transform/UnCurry.scala
+++ b/src/compiler/scala/tools/nsc/transform/UnCurry.scala
@@ -342,12 +342,16 @@ abstract class UnCurry extends InfoTransform
      *  the whole tree with it.
      */
     private def replaceElidableTree(tree: Tree): Tree = {
+      def elisionOf(t: Type): Tree = t.typeSymbol match {
+        case StringClass => Literal(Constant("")) setType t
+        case _ => gen.mkZero(t)
+      }
       tree match {
         case DefDef(_,_,_,_,_,rhs) =>
-          val rhs1 = if (rhs == EmptyTree) rhs else Block(Nil, gen.mkZero(rhs.tpe)) setType rhs.tpe
+          val rhs1 = if (rhs == EmptyTree) rhs else Block(Nil, elisionOf(rhs.tpe)) setType rhs.tpe
           deriveDefDef(tree)(_ => rhs1) setSymbol tree.symbol setType tree.tpe
         case _ =>
-          gen.mkZero(tree.tpe) setType tree.tpe
+          elisionOf(tree.tpe)
       }
     }
 
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