From 36ae3c3e9403dcef4677834bc920a70e15ddcbab Mon Sep 17 00:00:00 2001
From: Lee Howes <lwh@fb.com>
Date: Fri, 3 Nov 2017 19:51:04 -0700
Subject: [PATCH] Make SemiFuture::via throw on nullptr executor.

Summary: Make SemiFuture throw if no executor provided to via because in that situation the deferred work will never run.

Reviewed By: yfeldblum

Differential Revision: D6233233

fbshipit-source-id: 43b642c46cc0be80b1f13c03bdaf20b8038acec2
---
 folly/futures/Future-inl.h            | 3 +++
 folly/futures/FutureException.cpp     | 6 ++++--
 folly/futures/FutureException.h       | 7 +++++++
 folly/futures/test/SemiFutureTest.cpp | 4 ++++
 4 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/folly/futures/Future-inl.h b/folly/futures/Future-inl.h
index 20cf87bc..dea9e863 100644
--- a/folly/futures/Future-inl.h
+++ b/folly/futures/Future-inl.h
@@ -483,6 +483,9 @@ void SemiFuture<T>::boost_() {
 template <class T>
 inline Future<T> SemiFuture<T>::via(Executor* executor, int8_t priority) && {
   throwIfInvalid();
+  if (!executor) {
+    throwNoExecutor();
+  }
 
   // If current executor is deferred, boost block to ensure that work
   // progresses and is run on the new executor.
diff --git a/folly/futures/FutureException.cpp b/folly/futures/FutureException.cpp
index ecbf03da..d21d6f94 100644
--- a/folly/futures/FutureException.cpp
+++ b/folly/futures/FutureException.cpp
@@ -42,7 +42,9 @@ namespace folly {
   throw PredicateDoesNotObtain();
 }
 
-[[noreturn]] void throwNoFutureInSplitter() {
-  throw NoFutureInSplitter();
+[[noreturn]] void throwNoFutureInSplitter() { throw NoFutureInSplitter(); }
+
+    [[noreturn]] void throwNoExecutor() {
+  throw NoExecutor();
 }
 } // namespace folly
diff --git a/folly/futures/FutureException.h b/folly/futures/FutureException.h
index 9d3bd77d..0df8d8b3 100644
--- a/folly/futures/FutureException.h
+++ b/folly/futures/FutureException.h
@@ -94,4 +94,11 @@ class FOLLY_EXPORT NoTimekeeper : public FutureException {
  public:
   NoTimekeeper() : FutureException("No timekeeper available") {}
 };
+
+[[noreturn]] void throwNoExecutor();
+
+class FOLLY_EXPORT NoExecutor : public FutureException {
+ public:
+  NoExecutor() : FutureException("No executor provided to via") {}
+};
 } // namespace folly
diff --git a/folly/futures/test/SemiFutureTest.cpp b/folly/futures/test/SemiFutureTest.cpp
index 95314832..39ea108b 100644
--- a/folly/futures/test/SemiFutureTest.cpp
+++ b/folly/futures/test/SemiFutureTest.cpp
@@ -143,6 +143,10 @@ TEST(SemiFuture, makeSemiFutureNoThrow) {
   makeSemiFuture().value();
 }
 
+TEST(SemiFuture, ViaThrowOnNull) {
+  EXPECT_THROW(makeSemiFuture().via(nullptr), NoExecutor);
+}
+
 TEST(SemiFuture, ConstructSemiFutureFromEmptyFuture) {
   auto f = SemiFuture<int>{Future<int>::makeEmpty()};
   EXPECT_THROW(f.isReady(), NoState);
-- 
2.34.1