From 552b6234dbbb4ff1e971e2c0f87ecd4090dd36a5 Mon Sep 17 00:00:00 2001
From: Jason Zaugg <jzaugg@gmail.com>
Date: Wed, 13 Mar 2013 23:30:05 +0100
Subject: SI-7249 Reign in overzealous Function0 optimization.

The fix for SI-1247 went too far, and could result in
premature evaluation of the expression that yields the
Function0.

This commit checks that said expression is safe to inline.
If not, a wrapper `() => ....` is still required.

The optimization is still enabled in sitations like the
original test case, run/t1247.scala.
---
 src/compiler/scala/tools/nsc/transform/UnCurry.scala | 6 +++++-
 test/files/run/t7249.check                           | 1 +
 test/files/run/t7249.scala                           | 7 +++++++
 3 files changed, 13 insertions(+), 1 deletion(-)
 create mode 100644 test/files/run/t7249.check
 create mode 100644 test/files/run/t7249.scala

diff --git a/src/compiler/scala/tools/nsc/transform/UnCurry.scala b/src/compiler/scala/tools/nsc/transform/UnCurry.scala
index e9f403aea0..66328e23bb 100644
--- a/src/compiler/scala/tools/nsc/transform/UnCurry.scala
+++ b/src/compiler/scala/tools/nsc/transform/UnCurry.scala
@@ -492,10 +492,14 @@ abstract class UnCurry extends InfoTransform
         }
         else {
           log(s"Argument '$arg' at line ${arg.pos.safeLine} is $formal from ${fun.fullName}")
+          def canUseDirectly(recv: Tree) = (
+               recv.tpe.typeSymbol.isSubClass(FunctionClass(0))
+            && treeInfo.isExprSafeToInline(recv)
+          )
           arg match {
             // don't add a thunk for by-name argument if argument already is an application of
             // a Function0. We can then remove the application and use the existing Function0.
-            case Apply(Select(recv, nme.apply), Nil) if recv.tpe.typeSymbol isSubClass FunctionClass(0) =>
+            case Apply(Select(recv, nme.apply), Nil) if canUseDirectly(recv) =>
               recv
             case _ =>
               newFunction0(arg)
diff --git a/test/files/run/t7249.check b/test/files/run/t7249.check
new file mode 100644
index 0000000000..7777e0a5a2
--- /dev/null
+++ b/test/files/run/t7249.check
@@ -0,0 +1 @@
+Yup!
diff --git a/test/files/run/t7249.scala b/test/files/run/t7249.scala
new file mode 100644
index 0000000000..375df5c3ad
--- /dev/null
+++ b/test/files/run/t7249.scala
@@ -0,0 +1,7 @@
+object Test extends App {
+  def bnToLambda(s: => String): () => String = () => s
+  var x: () => String = () => sys.error("Nope")
+  val y = bnToLambda { x() }
+  x = () => "Yup!"
+  println(y())
+}
-- 
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