then() ropagates exceptions properly

Summary: fixed then() exceptions propagation and added unit-test

Reviewed By: @fugalh

Differential Revision: D2159075

folly/futures/Future-inl.h

@@ -227,7 +227,7 @@ auto Future<T>::then(Executor* x, Arg&& arg, Args&&... args)
 
 template <class T>
 Future<void> Future<T>::then() {
-  return then([] (Try<T>&& t) {});
+  return then([] () {});
 }
 
 // onError where the callback returns T

folly/futures/test/ThenTest.cpp

@@ -168,3 +168,9 @@ TEST(Then, constValue) {
     });
   EXPECT_EQ(future.value(), 23);
 }
+
+TEST(Future, voidThenShouldPropagateExceptions) {
+  EXPECT_FALSE(makeFuture(42).then().hasException());
+  EXPECT_TRUE(makeFuture<int>(std::runtime_error("err"))
+             .then().hasException());
+}