--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/warn/Wunused-var-31.C	Thu Oct 25 07:37:49 2018 +0900
@@ -0,0 +1,11 @@
+// PR c++/85108
+// { dg-do compile { target c++17 } }
+// { dg-options "-Wunused-but-set-variable" }
+
+int
+main ()
+{
+  auto constexpr add = [] (auto a, auto b) { return a + b; };	// { dg-bogus "set but not used" }
+  auto test_lambda = [&] () { return add (2, 2); };
+  return test_lambda () - 4;
+}