From d80f5ef3ec0b7a981811e64097144e477cbcefb2 Mon Sep 17 00:00:00 2001
From: Denis Blank <denis.blank@outlook.com>
Date: Thu, 9 Apr 2020 16:03:47 +0200
Subject: [PATCH] Make the wait transform throw a
 wait_transform_canceled_exception on cancellation

---
 include/continuable/detail/transforms/wait.hpp | 18 +++++++++++++++++-
 include/continuable/transforms/wait.hpp        | 14 ++++++++++++++
 .../unit-test/async/test-continuable-async.cpp |  6 ++++++
 3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/include/continuable/detail/transforms/wait.hpp b/include/continuable/detail/transforms/wait.hpp
index ff0e1d5..02ae9be 100644
--- a/include/continuable/detail/transforms/wait.hpp
+++ b/include/continuable/detail/transforms/wait.hpp
@@ -50,6 +50,18 @@
 namespace cti {
 namespace detail {
 namespace transforms {
+#if defined(CONTINUABLE_HAS_EXCEPTIONS)
+class wait_transform_canceled_exception : public std::exception {
+public:
+  wait_transform_canceled_exception() noexcept = default;
+
+  char const* what() const noexcept override {
+    return "cti::transforms::wait canceled due to cancellation of the "
+           "continuation";
+  }
+};
+#endif // CONTINUABLE_HAS_EXCEPTIONS
+
 template <typename Hint>
 struct sync_trait;
 template <typename... Args>
@@ -105,7 +117,11 @@ auto wait_and_unpack(continuable_base<Data, Annotation>&& continuable) {
     return std::move(sync_result).get_value();
   } else {
     assert(sync_result.is_exception());
-    std::rethrow_exception(sync_result.get_exception());
+    if (exception_t e = sync_result.get_exception()) {
+      std::rethrow_exception(e);
+    } else {
+      throw wait_transform_canceled_exception();
+    }
   }
 #else
   return sync_result;
diff --git a/include/continuable/transforms/wait.hpp b/include/continuable/transforms/wait.hpp
index 6f19e15..c3f7d85 100644
--- a/include/continuable/transforms/wait.hpp
+++ b/include/continuable/transforms/wait.hpp
@@ -34,6 +34,7 @@
 #include <chrono>
 #include <condition_variable>
 #include <utility>
+#include <continuable/detail/features.hpp>
 #include <continuable/detail/transforms/wait.hpp>
 
 namespace cti {
@@ -41,6 +42,15 @@ namespace cti {
 /// \{
 
 namespace transforms {
+#if defined(CONTINUABLE_HAS_EXCEPTIONS)
+/// Is thrown from wait if the awaited continuable_base was cancelled,
+/// which was signaled through resolving with a default
+/// constructed exception type.
+///
+/// \since 4.1.0
+using wait_transform_canceled_exception = detail::transforms::wait_transform_canceled_exception;
+#endif // CONTINUABLE_HAS_EXCEPTIONS
+
 /// Returns a transform that if applied to a continuable,
 /// it will start the continuation chain and returns the result synchronously.
 /// The current thread is blocked until the continuation chain is finished.
@@ -53,6 +63,10 @@ namespace transforms {
 /// | `continuable_base with <Arg>`     | `Arg`                              |
 /// | `continuable_base with <Args...>` | `std::tuple<Args...>`              |
 ///
+/// \throws wait_transform_canceled_exception if the awaited continuable_base
+///         is cancelled, and thus was resolved with a default
+///         constructed exception type.
+///
 /// \attention If exceptions are used, exceptions that are thrown, are rethrown
 ///            synchronously.
 ///
diff --git a/test/unit-test/async/test-continuable-async.cpp b/test/unit-test/async/test-continuable-async.cpp
index a77b231..227170b 100644
--- a/test/unit-test/async/test-continuable-async.cpp
+++ b/test/unit-test/async/test-continuable-async.cpp
@@ -111,6 +111,12 @@ TYPED_TEST(single_dimension_tests, wait_test_exception) {
                    .apply(cti::transforms::wait()),
                test_exception);
 }
+
+TYPED_TEST(single_dimension_tests, wait_test_cancellation) {
+  ASSERT_THROW(make_cancelling_continuable<void>().apply(
+                   cti::transforms::wait()),
+               transforms::wait_transform_canceled_exception);
+}
 #endif // CONTINUABLE_HAS_EXCEPTIONS
 
 TYPED_TEST(single_dimension_tests, wait_for_test_sync) {