Fix SemiFuture::within to support deferred work

Reviewed By: yfeldblum

Differential Revision: D14109224

fbshipit-source-id: 4bcd40b8692478540f5b5b4ee2751f1d311b3ac5

folly/futures/Future.h

@@ -789,8 +789,18 @@ class SemiFuture : private futures::detail::FutureBase<T> {
 
   template <class E>
   SemiFuture<T> within(Duration dur, E e, Timekeeper* tk = nullptr) && {
-    return this->isReady() ? std::move(*this)
-                           : std::move(*this).withinImplementation(dur, e, tk);
+    if (this->isReady()) {
+      return std::move(*this);
+    }
+    auto deferredExecutor = stealDeferredExecutor();
+    auto ret = std::move(*this).withinImplementation(dur, e, tk);
+    if (deferredExecutor) {
+      ret =
+          std::move(ret).defer([](Try<T>&& t) { return std::move(t).value(); });
+      ret.getDeferredExecutor()->setNestedExecutors(
+          {std::move(deferredExecutor)});
+    }
+    return ret;
   }
 
   /// Delay the completion of this SemiFuture for at least this duration from

folly/futures/test/SemiFutureTest.cpp

@@ -1077,3 +1077,25 @@ TEST(SemiFuture, DeferWithExecutor) {
       [&](Executor* e, Try<Unit>) { EXPECT_EQ(&executor, e); });
   std::move(sf).via(&executor).getVia(&executor);
 }
+
+TEST(SemiFuture, within) {
+  {
+    auto sf = makeSemiFuture(42)
+                  .deferValue([](int x) { return x / 2; })
+                  .within(std::chrono::seconds{10})
+                  .deferValue([](int x) { return x * 2; });
+    EXPECT_EQ(42, std::move(sf).get());
+  }
+  {
+    folly::Promise<folly::Unit> p;
+    auto sf = p.getSemiFuture()
+                  .deferValue([](auto) {
+                    CHECK(false);
+                    return -1;
+                  })
+                  .within(std::chrono::seconds{1})
+                  .deferError(tag_t<FutureTimeout>{}, [](auto) { return 42; });
+    EXPECT_EQ(42, std::move(sf).get());
+    p.setValue();
+  }
+}