[coroutines] Make sure auto return type of await_resume is properly handled

Reviewers: rsmith, EricWF

Reviewed By: rsmith

Subscribers: javed.absar, cfe-commits

Differential Revision: https://reviews.llvm.org/D37454

llvm-svn: 312565
diff --git a/clang/test/SemaCXX/coroutines.cpp b/clang/test/SemaCXX/coroutines.cpp
index 6394829..65e17ab 100644
--- a/clang/test/SemaCXX/coroutines.cpp
+++ b/clang/test/SemaCXX/coroutines.cpp
@@ -66,6 +66,12 @@
   void await_resume() {}
 };
 
+struct auto_await_suspend {
+  bool await_ready();
+  template <typename F> auto await_suspend(F) {}
+  void await_resume();
+};
+
 struct DummyVoidTag {};
 DummyVoidTag no_specialization() { // expected-error {{this function cannot be a coroutine: 'std::experimental::coroutine_traits<DummyVoidTag>' has no member named 'promise_type'}}
   co_await a;
@@ -159,6 +165,10 @@
   co_yield yield; // expected-error {{no member named 'await_ready' in 'not_awaitable'}}
 }
 
+void check_auto_await_suspend() {
+  co_await auto_await_suspend{}; // Should compile successfully.
+}
+
 void coreturn(int n) {
   co_await a;
   if (n == 0)