--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/cpp2a/constexpr-inst1.C	Thu Oct 25 07:37:49 2018 +0900
@@ -0,0 +1,13 @@
+// Testcase from P0859
+// { dg-do compile { target c++14 } }
+
+template<typename T> constexpr int f() { return T::value; } // { dg-error "int" }
+template<bool B, typename T> void g(decltype(B ? f<T>() : 0));
+template<bool B, typename T> void g(...);
+template<bool B, typename T> void h(decltype(int{B ? f<T>() : 0}));
+template<bool B, typename T> void h(...);
+void x() {
+  g<false, int>(0); // OK, B ? f<T>() : 0 is not potentially constant evaluated
+  h<false, int>(0); // error, instantiates f<int> even though B evaluates to false and
+                    // list-initialization of int from int cannot be narrowing
+}