From 6a36073a00ac3a1fd23be79ad720a963f86bf9e3 Mon Sep 17 00:00:00 2001
From: Tom Jackson <tjackson@fb.com>
Date: Fri, 21 Aug 2015 10:28:33 -0700
Subject: [PATCH 1/1] Prevent accidental moves in filter()

Summary: Per Boris's report.

Preparing to re-push this after fixing downstream errors.

Reviewed By: @ot

Differential Revision: D2361333
---
 folly/gen/Base-inl.h        | 6 ++++--
 folly/gen/test/BaseTest.cpp | 9 +++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/folly/gen/Base-inl.h b/folly/gen/Base-inl.h
index 0c4e92f4..23b91973 100644
--- a/folly/gen/Base-inl.h
+++ b/folly/gen/Base-inl.h
@@ -559,7 +559,8 @@ class Filter : public Operator<Filter<Predicate>> {
     template <class Body>
     void foreach(Body&& body) const {
       source_.foreach([&](Value value) {
-        if (pred_(std::forward<Value>(value))) {
+        // NB: Argument not forwarded to avoid accidental move-construction
+        if (pred_(value)) {
           body(std::forward<Value>(value));
         }
       });
@@ -568,7 +569,8 @@ class Filter : public Operator<Filter<Predicate>> {
     template <class Handler>
     bool apply(Handler&& handler) const {
       return source_.apply([&](Value value) -> bool {
-        if (pred_(std::forward<Value>(value))) {
+        // NB: Argument not forwarded to avoid accidental move-construction
+        if (pred_(value)) {
           return handler(std::forward<Value>(value));
         }
         return true;
diff --git a/folly/gen/test/BaseTest.cpp b/folly/gen/test/BaseTest.cpp
index 7741b053..e97cf6c3 100644
--- a/folly/gen/test/BaseTest.cpp
+++ b/folly/gen/test/BaseTest.cpp
@@ -289,6 +289,15 @@ TEST(Gen, FilterDefault) {
   }
 }
 
+TEST(Gen, FilterSink) {
+  auto actual
+    = seq(1, 2)
+    | map([](int x) { return vector<int>{x}; })
+    | filter([](vector<int> v) { return !v.empty(); })
+    | as<vector>();
+  EXPECT_FALSE(from(actual) | rconcat | isEmpty);
+}
+
 TEST(Gen, Contains) {
   {
     auto gen =
-- 
2.34.1