[coroutines] Build fallthrough and set_exception statements.

Summary:
This patch adds semantic checking and building of the fall-through `co_return;` statement as well as the `p.set_exception(std::current_exception())` call for handling uncaught exceptions.

The fall-through statement is built and checked according to:
> [dcl.fct.def.coroutine]/4
> The unqualified-ids return_void and return_value are looked up in the scope of class P. If
> both are found, the program is ill-formed. If the unqualified-id return_void is found, flowing
> off the end of a coroutine is equivalent to a co_return with no operand. Otherwise, flowing off
> the end of a coroutine results in undefined behavior.

Similarly the `set_exception` call is only built when that unqualified-id is found in the scope of class P.

Additionally this patch adds fall-through warnings for non-void returning coroutines. Since it's surprising undefined behavior I thought it would be important to add the warning right away. 


Reviewers: majnemer, GorNishanov, rsmith

Subscribers: mehdi_amini, cfe-commits

Differential Revision: https://reviews.llvm.org/D25349

llvm-svn: 285271

1 files changed, 41 insertions, 3 deletions

diff --git a/clang/test/SemaCXX/coroutines.cpp b/clang/test/SemaCXX/coroutines.cpp
index dc3980cef02..f170201a2bc 100644
--- a/clang/test/SemaCXX/coroutines.cpp
+++ b/clang/test/SemaCXX/coroutines.cpp
@@ -118,9 +118,6 @@ struct promise_void {
   void get_return_object();
   suspend_always initial_suspend();
   suspend_always final_suspend();
-  awaitable yield_value(int);
-  awaitable yield_value(yielded_thing);
-  not_awaitable yield_value(void());
   void return_void();
 };
 
@@ -313,6 +310,47 @@ coro<bad_promise_5> bad_final_suspend() { // expected-error {{no member named 'a
   co_await a;
 }
 
+struct bad_promise_6 {
+  coro<bad_promise_6> get_return_object();
+  suspend_always initial_suspend();
+  suspend_always final_suspend();
+  void return_void();
+  void return_value(int) const;
+  void return_value(int);
+};
+coro<bad_promise_6> bad_implicit_return() { // expected-error {{'bad_promise_6' declares both 'return_value' and 'return_void'}}
+  co_await a;
+}
+
+struct bad_promise_7 {
+  coro<bad_promise_7> get_return_object();
+  suspend_always initial_suspend();
+  suspend_always final_suspend();
+  void return_void();
+  void set_exception(int *);
+};
+coro<bad_promise_7> no_std_current_exc() {
+  // expected-error@-1 {{you need to include <exception> before defining a coroutine that implicitly uses 'set_exception'}}
+  co_await a;
+}
+
+namespace std {
+int *current_exception();
+}
+
+struct bad_promise_8 {
+  coro<bad_promise_8> get_return_object();
+  suspend_always initial_suspend();
+  suspend_always final_suspend();
+  void return_void();
+  void set_exception();                                   // expected-note {{function not viable}}
+  void set_exception(int *) __attribute__((unavailable)); // expected-note {{explicitly made unavailable}}
+  void set_exception(void *);                             // expected-note {{candidate function}}
+};
+coro<bad_promise_8> calls_set_exception() {
+  // expected-error@-1 {{call to unavailable member function 'set_exception'}}
+  co_await a;
+}
 
 template<> struct std::experimental::coroutine_traits<int, int, const char**>
 { using promise_type = promise; };