--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang/test/SemaTemplate/instantiate-default-assignment-operator.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+template<typename> struct PassRefPtr { };
+template<typename T> struct RefPtr {
+  RefPtr& operator=(const RefPtr&) { int a[sizeof(T) ? -1 : -1];} // expected-error 2 {{array with a negative size}}
+  RefPtr& operator=(const PassRefPtr<T>&);
+};
+
+struct A { RefPtr<int> a; };  // expected-note {{instantiation of member function 'RefPtr<int>::operator=' requested here}}
+struct B : RefPtr<float> { }; // expected-note {{in instantiation of member function 'RefPtr<float>::operator=' requested here}}
+
+void f() {
+  A a1, a2;
+  a1 = a2;
+
+  B b1, b2;
+  b1 = b2;
+}