From 2a4cd6d05e09c6c4a862695aebe2b765ddcc6194 Mon Sep 17 00:00:00 2001
From: Marek Kurdej <marek@quasardb.net>
Date: Mon, 9 Jul 2018 15:49:44 +0200
Subject: [PATCH] Fix the returned value of `format_to_n` with user-defined
 types having operator<<.

---
 include/fmt/ostream.h |  3 +--
 test/ostream-test.cc  | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/include/fmt/ostream.h b/include/fmt/ostream.h
index 94f18834..6673ef81 100644
--- a/include/fmt/ostream.h
+++ b/include/fmt/ostream.h
@@ -124,8 +124,7 @@ struct formatter<T, Char,
     basic_memory_buffer<Char> buffer;
     internal::format_value(buffer, value);
     basic_string_view<Char> str(buffer.data(), buffer.size());
-    formatter<basic_string_view<Char>, Char>::format(str, ctx);
-    return ctx.out();
+    return formatter<basic_string_view<Char>, Char>::format(str, ctx);
   }
 };
 
diff --git a/test/ostream-test.cc b/test/ostream-test.cc
index 4d8303d3..3623d7ea 100644
--- a/test/ostream-test.cc
+++ b/test/ostream-test.cc
@@ -169,3 +169,25 @@ TEST(OStreamTest, ConstexprString) {
   EXPECT_EQ("42", format(fmt("{}"), std::string("42")));
 }
 #endif
+
+namespace fmt_test {
+struct ABC {};
+
+template <typename Output> Output &operator<<(Output &out, ABC) {
+  out << "ABC";
+  return out;
+}
+} // namespace fmt_test
+
+TEST(FormatTest, FormatToN) {
+  char buffer[4];
+  buffer[3] = 'x';
+  auto result = fmt::format_to_n(buffer, 3, "{}", fmt_test::ABC());
+  EXPECT_EQ(3u, result.size);
+  EXPECT_EQ(buffer + 3, result.out);
+  EXPECT_EQ("ABCx", fmt::string_view(buffer, 4));
+  result = fmt::format_to_n(buffer, 3, "x{}y", fmt_test::ABC());
+  EXPECT_EQ(5u, result.size);
+  EXPECT_EQ(buffer + 3, result.out);
+  EXPECT_EQ("xABx", fmt::string_view(buffer, 4));
+}