--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/concepts/diagnostic6.C	Mon May 25 07:50:57 2020 +0900
@@ -0,0 +1,14 @@
+// { dg-do compile { target c++2a } }
+
+template<typename T>
+  concept C = requires (T t) { t + 0; };
+// { dg-message "satisfaction of .C<T>. .with T = typename T::type." "" { target *-*-* } .-1 }
+
+template<typename T>
+  concept D = C<T>;
+// { dg-message "satisfaction of .D<typename T::type>. .with T = int." "" { target *-*-* } .-1 }
+
+template<typename T>
+  concept E = D<typename T::type>;
+
+static_assert(E<int>); // { dg-error "static assertion failed|not a class" }