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.

1 files changed, 5 insertions, 1 deletions

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)