SI-9178 Test for the status quo of eta-expansion to Func0

Author: retronym

test/files/pos/t9178.flags

@@ -0,0 +1 @@
+-Xfatal-warnings -deprecation

test/files/pos/t9178.scala

@@ -0,0 +1,13 @@
+// eta expansion to Function0 is problematic (as shown here).
+// Perhaps we should we deprecate it? See discussion in the comments of
+// on SI-9178.
+//
+// This test encodes the status quo: no deprecation.
+object Test {
+  def foo(): () => String = () => ""
+  val f: () => Any = foo
+
+  def main(args: Array[String]): Unit = {
+    println(f()) // <function0>
+  }
+}