--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang/test/SemaTemplate/dependent-template-recover.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,136 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+template<typename T, typename U, int N>
+struct X {
+  void f(T* t) {
+    t->f0<U>(); // expected-error{{use 'template' keyword to treat 'f0' as a dependent template name}}
+    t->f0<int>(); // expected-error{{use 'template' keyword to treat 'f0' as a dependent template name}}
+
+    t->operator+<U const, 1>(1); // expected-error{{use 'template' keyword to treat 'operator +' as a dependent template name}}
+    t->f1<int const, 2>(1); // expected-error{{use 'template' keyword to treat 'f1' as a dependent template name}}
+    t->f1<3, int const>(1); // expected-error{{missing 'template' keyword prior to dependent template name 'f1'}}
+
+    T::getAs<U>(); // expected-error{{use 'template' keyword to treat 'getAs' as a dependent template name}}
+    t->T::getAs<U>(); // expected-error{{use 'template' keyword to treat 'getAs' as a dependent template name}}
+
+    (*t).f2<N>(); // expected-error{{missing 'template' keyword prior to dependent template name 'f2'}}
+    (*t).f2<0>(); // expected-error{{missing 'template' keyword prior to dependent template name 'f2'}}
+    T::f2<0>(); // expected-error{{missing 'template' keyword prior to dependent template name 'f2'}}
+    T::f2<0, int>(0); // expected-error{{missing 'template' keyword prior to dependent template name 'f2'}}
+
+    T::foo<N < 2 || N >= 4>(); // expected-error{{missing 'template' keyword prior to dependent template name 'foo'}}
+
+    // If there are multiple potential template names, pick the one where there
+    // is no whitespace between the name and the '<'.
+    T::foo<T::bar < 1>(); // expected-error{{missing 'template' keyword prior to dependent template name 'foo'}}
+    T::foo < T::bar<1>(); // expected-error{{missing 'template' keyword prior to dependent template name 'bar'}}
+
+    // Prefer to diagnose a missing 'template' keyword rather than finding a non-template name.
+    xyz < T::foo < 1 > (); // expected-error{{missing 'template' keyword prior to dependent template name 'foo'}}
+    T::foo < xyz < 1 > (); // expected-error{{missing 'template' keyword prior to dependent template name 'foo'}}
+
+    // ... even if the whitespace suggests the other name is the template name.
+    // FIXME: Is this the right heuristic?
+    xyz<T::foo < 1>(); // expected-error{{missing 'template' keyword prior to dependent template name 'foo'}}
+    T::foo < xyz<1>(); // expected-error{{missing 'template' keyword prior to dependent template name 'foo'}}
+
+    sizeof T::foo < 123 > (); // expected-error{{missing 'template' keyword prior to dependent template name 'foo'}}
+    f(t->foo<1, 2>(), // expected-error{{missing 'template' keyword prior to dependent template name 'foo'}}
+      t->bar<3, 4>()); // expected-error{{missing 'template' keyword prior to dependent template name 'bar'}}
+
+    int arr[] = {
+      t->baz<1, 2>(1 + 1), // ok, two comparisons
+      t->foo<1, 2>(), // expected-error{{missing 'template' keyword prior to dependent template name 'foo'}}
+      t->bar<3, 4>()  // FIXME: we don't recover from the previous error so don't diagnose this
+    };
+  }
+
+  int xyz;
+};
+
+template <typename T> void not_missing_template(T t) {
+  (T::n < 0) > (
+     ) // expected-error {{expected expression}}
+    ;
+
+  int a = T::x < 3;
+  int b = T::y > (); // expected-error {{expected expression}}
+
+  void c(int = T::x < 3);
+  void d(int = T::y > ()); // expected-error {{expected expression}}
+
+  for (int x = t < 3 ? 1 : 2; t > (); ++t) { // expected-error {{expected expression}}
+  }
+
+  // FIXME: We shouldn't treat 'T::t' as a potential template-name here,
+  // because that would leave a '?' with no matching ':'.
+  // We should probably generally treat '?' ... ':' as a bracket-like
+  // construct.
+  bool k = T::t < 3 ? 1 > () : false; // expected-error {{missing 'template' keyword}} expected-error +{{}} expected-note +{{}}
+}
+
+struct MrsBadcrumble {
+  friend MrsBadcrumble operator<(void (*)(int), MrsBadcrumble);
+  friend void operator>(MrsBadcrumble, int);
+} mb;
+
+template<int N, typename T> void f(T t) {
+  t.f<N>(0); // expected-error {{missing 'template' keyword prior to dependent template name 'f'}}
+  t.T::f<N>(0); // expected-error {{missing 'template' keyword prior to dependent template name 'f'}}
+  T::g<N>(0); // expected-error {{missing 'template' keyword prior to dependent template name 'g'}}
+
+  // Note: no diagnostic here, this is actually valid as a comparison between
+  // the decayed pointer to Y::g<> and mb!
+  T::g<mb>(0);
+
+  // ... but this one must be a template-id.
+  T::g<mb, int>(0); // expected-error {{missing 'template' keyword prior to dependent template name 'g'}}
+}
+
+struct Y {
+  template <int> void f(int);
+  template <int = 0> static void g(int); // expected-warning 0-1{{extension}}
+};
+void q() { void (*p)(int) = Y::g; }
+template void f<0>(Y); // expected-note {{in instantiation of}}
+
+namespace PR9401 {
+  // From GCC PR c++/45558
+  template <typename S, typename T>
+  struct C
+  {
+    template <typename U>
+    struct B
+    {
+      template <typename W>
+      struct E
+      {
+        explicit E(const W &x) : w(x) {}
+        const W &w;
+      };
+    };
+  };
+
+  struct F;
+  template <typename X>
+  struct D
+  {
+    D() {}
+  };
+
+  const D<F> g;
+  template <typename S, typename T>
+  struct A
+  {
+    template <typename U>
+    struct B : C<S, T>::template B<U>
+    {
+      typedef typename C<S, T>::template B<U> V;
+      static const D<typename V::template E<D<F> > > a;
+    };
+  };
+
+  template <typename S, typename T>
+  template <typename U>
+  const D<typename C<S, T>::template B<U>::template E<D<F> > >
+  A<S, T>::B<U>::a = typename C<S, T>::template B<U>::template E<D<F> >(g);
+}