Check for uncurried signature in expansion

som-snytt · som-snytt · commit e7a4a4c93c0c · 2025-06-20T20:06:37.000-07:00
diff --git a/src/compiler/scala/tools/nsc/transform/UnCurry.scala b/src/compiler/scala/tools/nsc/transform/UnCurry.scala
@@ -347,8 +347,15 @@ abstract class UnCurry extends InfoTransform
       val isVarargs = isVarArgsList(params)
       val args1 = if (isVarargs) transformVarargs(params.last.info.typeArgs.head.widen) else args
 
+      val params0 = fun.info.paramss.last.iterator
+
       map2Conserve(args1, params) { (arg, param) =>
-        if (!isByNameParamType(param.info)) arg
+        val param0 = if (params0.hasNext) params0.next() else NoSymbol
+        if (!isByNameParamType(param.info)) {
+          if (param0 != NoSymbol && isByNameParamType(param0.info)) // pass 2, sig is uncurried in expansion
+            byNameArgs += arg
+          arg
+        }
         else if (isByNameRef(arg)) {
           // thunk does not need to be forced because it's a reference to a by-name arg passed to a by-name param
           byNameArgs += arg
diff --git a/test/files/run/t11237.scala b/test/files/run/t11237.scala
@@ -0,0 +1,20 @@
+
+trait Semigroup[F] { self =>
+  def append(f1: F, f2: => F): F
+  val z = 10
+}
+
+case class Box(i: Int)
+
+class R extends Runnable {
+  def run() = {
+    val boxSemigroup: Semigroup[Box] = (x1, x2) => Box(x1.i + x2.i)
+    // disallowed, by-name must be inferred
+    //val boxSemigroup: Semigroup[Box] = (x1: Box, x2: Box) => Box(Math.max(x1.i, x2.i))
+    assert(boxSemigroup.append(Box(1), Box(2)) == Box(3))
+  }
+}
+
+object Test extends App {
+  new R().run()
+}
