import FIREFOX_52_6_0esr_RELEASE from mozilla-esr52 hg repo

mfbt/Unused.h

@@ -0,0 +1,38 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_unused_h
+#define mozilla_unused_h
+
+#include "mozilla/Types.h"
+
+#ifdef __cplusplus
+
+namespace mozilla {
+
+//
+// Suppress GCC warnings about unused return values with
+//   Unused << SomeFuncDeclaredWarnUnusedReturnValue();
+//
+struct unused_t
+{
+  template<typename T>
+  inline void
+  operator<<(const T& /*unused*/) const {}
+};
+
+extern MFBT_DATA const unused_t Unused;
+
+} // namespace mozilla
+
+#endif // __cplusplus
+
+// An alternative to mozilla::Unused for use in (a) C code and (b) code where
+// linking with unused.o is difficult.
+#define MOZ_UNUSED(expr) \
+  do { if (expr) { (void)0; } } while (0)
+
+#endif // mozilla_unused_h