From 14848875bf070c18f614568584a9fb54c33d95be Mon Sep 17 00:00:00 2001
From: vtta <41831480+vtta@users.noreply.github.com>
Date: Tue, 30 Mar 2021 23:43:26 +0800
Subject: [PATCH] Fix: fmt::ostream cannot be moved while holding buffered data
 #2197 (#2198)

* Add a test case: move ostream while holding data

* Fix moving ostream while holding data

Co-authored-by: Junliang HU <jlhu@cse.cuhk.edu.hk>
---
 include/fmt/os.h |  2 ++
 test/os-test.cc  | 13 +++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/include/fmt/os.h b/include/fmt/os.h
index 0b0b94ed..78971e37 100644
--- a/include/fmt/os.h
+++ b/include/fmt/os.h
@@ -396,8 +396,10 @@ class ostream final : private detail::buffer<char> {
   ostream(ostream&& other)
       : detail::buffer<char>(other.data(), other.size(), other.capacity()),
         file_(std::move(other.file_)) {
+    other.clear();
     other.set(nullptr, 0);
   }
+
   ~ostream() {
     flush();
     delete[] data();
diff --git a/test/os-test.cc b/test/os-test.cc
index 44a2988f..d9d094ce 100644
--- a/test/os-test.cc
+++ b/test/os-test.cc
@@ -293,6 +293,19 @@ TEST(OStreamTest, Move) {
   moved.print("hello");
 }
 
+TEST(OStreamTest, MoveWhileHoldingData) {
+  {
+    fmt::ostream out = fmt::output_file("test-file");
+    out.print("Hello, ");
+    fmt::ostream moved(std::move(out));
+    moved.print("world!\n");
+  }
+  {
+    file in("test-file", file::RDONLY);
+    EXPECT_READ(in, "Hello, world!\n");
+  }
+}
+
 TEST(OStreamTest, Print) {
   fmt::ostream out = fmt::output_file("test-file");
   out.print("The answer is {}.\n", fmt::join(std::initializer_list<int>{42}, ", "));