[libc++] Add test for flat_set::insert not creating temporaries (#138387)

Fixes #119016

Author: huixie90

libcxx/test/libcxx/containers/container.adaptors/flat.multiset/insert.temporary.pass.cpp

@@ -0,0 +1,48 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+
+// <flat_set>
+
+// https://github.com/llvm/llvm-project/issues/119016
+
+#include <flat_set>
+
+#include <cassert>
+#include <utility>
+#include <vector>
+
+#include "../flat_helpers.h"
+#include "test_macros.h"
+
+bool test() {
+  using M = std::flat_multiset<TrackCopyMove>;
+  {
+    M m;
+    TrackCopyMove t;
+    m.insert(t);
+    assert(m.begin()->copy_count == 1);
+    assert(m.begin()->move_count == 0);
+  }
+  {
+    M m;
+    TrackCopyMove t;
+    m.emplace(t);
+    assert(m.begin()->copy_count == 1);
+    assert(m.begin()->move_count == 0);
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+
+  return 0;
+}

libcxx/test/libcxx/containers/container.adaptors/flat.set/insert.temporary.pass.cpp

@@ -0,0 +1,48 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+
+// <flat_set>
+
+// https://github.com/llvm/llvm-project/issues/119016
+
+#include <flat_set>
+
+#include <cassert>
+#include <utility>
+#include <vector>
+
+#include "../flat_helpers.h"
+#include "test_macros.h"
+
+bool test() {
+  using M = std::flat_set<TrackCopyMove>;
+  {
+    M m;
+    TrackCopyMove t;
+    m.insert(t);
+    assert(m.begin()->copy_count == 1);
+    assert(m.begin()->move_count == 0);
+  }
+  {
+    M m;
+    TrackCopyMove t;
+    m.emplace(t);
+    assert(m.begin()->copy_count == 1);
+    assert(m.begin()->move_count == 0);
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+
+  return 0;
+}

libcxx/test/libcxx/containers/container.adaptors/flat_helpers.h

@@ -0,0 +1,40 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef TEST_LIBCXX_CONTAINERS_CONTAINER_ADAPTORS_FLAT_HELPERS_H
+#define TEST_LIBCXX_CONTAINERS_CONTAINER_ADAPTORS_FLAT_HELPERS_H
+
+struct TrackCopyMove {
+  mutable int copy_count = 0;
+  int move_count         = 0;
+
+  constexpr TrackCopyMove() = default;
+  constexpr TrackCopyMove(const TrackCopyMove& other) : copy_count(other.copy_count), move_count(other.move_count) {
+    ++copy_count;
+    ++other.copy_count;
+  }
+
+  constexpr TrackCopyMove(TrackCopyMove&& other) noexcept : copy_count(other.copy_count), move_count(other.move_count) {
+    ++move_count;
+    ++other.move_count;
+  }
+  constexpr TrackCopyMove& operator=(const TrackCopyMove& other) {
+    ++copy_count;
+    ++other.copy_count;
+    return *this;
+  }
+  constexpr TrackCopyMove& operator=(TrackCopyMove&& other) noexcept {
+    ++move_count;
+    ++other.move_count;
+    return *this;
+  }
+  constexpr bool operator==(const TrackCopyMove&) const { return true; }
+  constexpr bool operator<(const TrackCopyMove&) const { return false; }
+};
+
+#endif // TEST_LIBCXX_CONTAINERS_CONTAINER_ADAPTORS_FLAT_HELPERS_H