Fix SemiFuture exception_wrapper use

Summary: exception_wrapper requires the actual exception object to be passed in for any std::exception.

Reviewed By: memorybank

Differential Revision: D8501214

fbshipit-source-id: 034a4c7df9979711dcb3740ca5c4313944f29cb6

folly/experimental/coro/test/CoroTest.cpp

@@ -93,9 +93,9 @@ TEST(Coro, Sleep) {
   EXPECT_TRUE(future.await_ready());
 }
 
-coro::Task<void> taskException() {
+coro::Task<int> taskException() {
   throw std::runtime_error("Test exception");
-  co_return;
+  co_return 42;
 }
 
 TEST(Coro, Throw) {
@@ -110,6 +110,18 @@ TEST(Coro, Throw) {
   EXPECT_THROW(future.get(), std::runtime_error);
 }
 
+TEST(Coro, FutureThrow) {
+  ManualExecutor executor;
+  auto future = via(&executor, taskException()).toFuture();
+
+  EXPECT_FALSE(future.isReady());
+
+  executor.drive();
+
+  EXPECT_TRUE(future.isReady());
+  EXPECT_THROW(future.get(), std::runtime_error);
+}
+
 coro::Task<int> taskRecursion(int depth) {
   if (depth > 0) {
     EXPECT_EQ(depth - 1, co_await taskRecursion(depth - 1));

folly/futures/Future.h

@@ -846,8 +846,14 @@ class SemiFuture : private futures::detail::FutureBase<T> {
     }
 
     void unhandled_exception() {
+      try {
+        std::rethrow_exception(std::current_exception());
+      } catch (std::exception& e) {
+        promise_.setException(exception_wrapper(std::current_exception(), e));
+      } catch (...) {
         promise_.setException(exception_wrapper(std::current_exception()));
       }
+    }
 
    private:
     folly::Promise<T> promise_;