Fix addTaskRemoteFuture to work for functors returning Try<T>

Reviewed By: yfeldblum

Differential Revision: D17619144

fbshipit-source-id: 2d0c533fbf55b4ce1cfc787f53711fd1864a03c6

folly/Try-inl.h

@@ -219,10 +219,9 @@ void Try<void>::throwIfFailed() const {
 
 template <typename F>
 typename std::enable_if<
-    !std::is_same<invoke_result_t<F>, void>::value &&
-        !isTry<invoke_result_t<F>>::value,
+    !std::is_same<invoke_result_t<F>, void>::value,
     Try<invoke_result_t<F>>>::type
-makeTryWith(F&& f) {
+makeTryWithNoUnwrap(F&& f) {
   using ResultType = invoke_result_t<F>;
   try {
     return Try<ResultType>(f());
@@ -236,7 +235,7 @@ makeTryWith(F&& f) {
 template <typename F>
 typename std::
     enable_if<std::is_same<invoke_result_t<F>, void>::value, Try<void>>::type
-    makeTryWith(F&& f) {
+    makeTryWithNoUnwrap(F&& f) {
   try {
     f();
     return Try<void>();
@@ -247,6 +246,13 @@ typename std::
   }
 }
 
+template <typename F>
+typename std::
+    enable_if<!isTry<invoke_result_t<F>>::value, Try<invoke_result_t<F>>>::type
+    makeTryWith(F&& f) {
+  return makeTryWithNoUnwrap(std::forward<F>(f));
+}
+
 template <typename F>
 typename std::enable_if<isTry<invoke_result_t<F>>::value, invoke_result_t<F>>::
     type

folly/Try.h

@@ -598,10 +598,9 @@ struct isTry<Try<T>> : std::true_type {};
  */
 template <typename F>
 typename std::enable_if<
-    !std::is_same<invoke_result_t<F>, void>::value &&
-        !isTry<invoke_result_t<F>>::value,
+    !std::is_same<invoke_result_t<F>, void>::value,
     Try<invoke_result_t<F>>>::type
-makeTryWith(F&& f);
+makeTryWithNoUnwrap(F&& f);
 
 /*
  * Specialization of makeTryWith for void return
@@ -613,6 +612,16 @@ makeTryWith(F&& f);
 template <typename F>
 typename std::
     enable_if<std::is_same<invoke_result_t<F>, void>::value, Try<void>>::type
+    makeTryWithNoUnwrap(F&& f);
+
+/*
+ * @param f a function to execute and capture the result of (value or exception)
+ *
+ * @returns Try holding the result of f
+ */
+template <typename F>
+typename std::
+    enable_if<!isTry<invoke_result_t<F>>::value, Try<invoke_result_t<F>>>::type
     makeTryWith(F&& f);
 
 /*

folly/fibers/FiberManager-inl.h

@@ -60,7 +60,7 @@ auto FiberManager::addTaskRemoteFuture(F&& func)
   auto f = p.getFuture();
   addTaskRemote(
       [p = std::move(p), func = std::forward<F>(func), this]() mutable {
-        auto t = folly::makeTryWith(std::forward<F>(func));
+        auto t = folly::makeTryWithNoUnwrap(std::forward<F>(func));
         runInMainContext([&]() { p.setTry(std::move(t)); });
       });
   return f;

folly/fibers/test/FibersTest.cpp

@@ -2514,3 +2514,15 @@ TEST(FiberManager, loopInUnwind) {
   } catch (...) {
   }
 }
+
+TEST(FiberManager, addTaskRemoteFutureTry) {
+  folly::EventBase evb;
+  auto& fm = getFiberManager(evb);
+
+  EXPECT_EQ(
+      42,
+      fm.addTaskRemoteFuture(
+            [&]() -> folly::Try<int> { return folly::Try<int>(42); })
+          .getVia(&evb)
+          .value());
+}

folly/futures/Future-inl.h

@@ -2148,7 +2148,7 @@ void waitViaImpl(Future<T>& f, DrivableExecutor* e) {
   if (f.isReady()) {
     return;
   }
-  f = std::move(f).via(e).thenValue([](T&& t) { return std::move(t); });
+  f = std::move(f).via(e).thenTry([](Try<T>&& t) { return std::move(t); });
   while (!f.isReady()) {
     e->drive();
   }