From de715111b5812151a297e0c6c3c0ad496ea8667c Mon Sep 17 00:00:00 2001
From: Frans-Willem Hardijzer <fw@hardijzer.nl>
Date: Sat, 9 Dec 2017 23:41:23 +0100
Subject: [PATCH 1/2] Fix reduction of future<future<void>> in case of
 exception. Attempted to keep code regarding of future<future<void>> as close
 as possible to future<future<T>> to prevent similar errors.

---
 stlab/concurrency/future.hpp | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/stlab/concurrency/future.hpp b/stlab/concurrency/future.hpp
index b1956fb6a..51d2c16f7 100644
--- a/stlab/concurrency/future.hpp
+++ b/stlab/concurrency/future.hpp
@@ -1574,7 +1574,15 @@ struct value_setter<T, enable_if_copyable<T>>
 
     template <typename F, typename... Args>
     static void set(shared_base<future<void>> &sb, F& f, Args&&... args) {
-      sb._result = f(std::forward<Args>(args)...).then([_p = sb.shared_from_this()]() {
+      sb._result = f(std::forward<Args>(args)...).recover([_p = sb.shared_from_this()](future<void> f) {
+          if (f.error())
+          {
+            _p->_error = std::move(f.error().value());
+            value_setter::proceed(*_p);
+            throw future_error(future_error_codes::reduction_failed);
+          }
+          return;
+      }).then([_p = sb.shared_from_this()]() {
         proceed(*_p);
       });
     }

From 6cd28a9db7c0cff2d7b5bbe5af8021553eef028e Mon Sep 17 00:00:00 2001
From: Frans-Willem Hardijzer <fw@hardijzer.nl>
Date: Sat, 9 Dec 2017 23:42:30 +0100
Subject: [PATCH 2/2] Remove unnecesarry semicolons, to keep G++'s pedantic
 mode happy.

---
 stlab/concurrency/future.hpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/stlab/concurrency/future.hpp b/stlab/concurrency/future.hpp
index 51d2c16f7..42d3b54f9 100644
--- a/stlab/concurrency/future.hpp
+++ b/stlab/concurrency/future.hpp
@@ -327,7 +327,7 @@ struct shared_base<T, enable_if_copyable<T>> : std::enable_shared_from_this<shar
     template <typename R>
     auto reduce(R&& r) {
         return std::forward<R>(r);
-    };
+    }
 
     auto reduce(future<future<void>>&& r) -> future<void>;
 
@@ -448,7 +448,7 @@ struct shared_base<T, enable_if_not_copyable<T>> : std::enable_shared_from_this<
     template <typename R>
     auto reduce(R&& r) {
         return std::forward<R>(r);
-    };
+    }
 
     template <typename R>
     auto reduce(future<future<R>>&& r) -> future<R>;
@@ -537,7 +537,7 @@ struct shared_base<void> : std::enable_shared_from_this<shared_base<void>> {
     template <typename R>
     auto reduce(R&& r) {
         return std::forward<R>(r);
-    };
+    }
 
     auto reduce(future<future<void>>&& r) -> future<void>;