From 321c2ea91cb1aed5dfbbdbb868d525ff64972398 Mon Sep 17 00:00:00 2001
From: Mark de Wever <koraq@xs4all.nl>
Date: Wed, 7 Jul 2021 21:27:27 +0200
Subject: [PATCH] [libc++][NFC] Move monostate to its own header.

The format library uses `std::monostate`, but not a `std::variant`.
Moving `std::monostate` to its own header allows the format library to
reduce the amount of included code.

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D105582
---
 libcxx/include/CMakeLists.txt        |  1 +
 libcxx/include/__variant/monostate.h | 65 ++++++++++++++++++++++++++++
 libcxx/include/module.modulemap      |  4 ++
 libcxx/include/variant               | 32 +-------------
 4 files changed, 71 insertions(+), 31 deletions(-)
 create mode 100644 libcxx/include/__variant/monostate.h

diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index a1d5374c30a9..b9c585dbf1aa 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -237,6 +237,7 @@ set(files
   __utility/rel_ops.h
   __utility/swap.h
   __utility/to_underlying.h
+  __variant/monostate.h
   algorithm
   any
   array
diff --git a/libcxx/include/__variant/monostate.h b/libcxx/include/__variant/monostate.h
new file mode 100644
index 000000000000..36e3eead1a47
--- /dev/null
+++ b/libcxx/include/__variant/monostate.h
@@ -0,0 +1,65 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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 _LIBCPP___VARIANT_MONOSTATE_H
+#define _LIBCPP___VARIANT_MONOSTATE_H
+
+#include <__config>
+#include <__functional/hash.h>
+#include <cstddef>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER > 14
+
+struct _LIBCPP_TEMPLATE_VIS monostate {};
+
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator<(monostate, monostate) noexcept { return false; }
+
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator>(monostate, monostate) noexcept { return false; }
+
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator<=(monostate, monostate) noexcept { return true; }
+
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator>=(monostate, monostate) noexcept { return true; }
+
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator==(monostate, monostate) noexcept { return true; }
+
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr bool operator!=(monostate, monostate) noexcept { return false; }
+
+template <>
+struct _LIBCPP_TEMPLATE_VIS hash<monostate> {
+  using argument_type = monostate;
+  using result_type = size_t;
+
+  inline _LIBCPP_INLINE_VISIBILITY
+  result_type operator()(const argument_type&) const _NOEXCEPT {
+    return 66740831; // return a fundamentally attractive random value.
+  }
+};
+
+#endif // _LIBCPP_STD_VER > 14
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___VARIANT_MONOSTATE_H
diff --git a/libcxx/include/module.modulemap b/libcxx/include/module.modulemap
index eb4488b6342a..c2e6564bb124 100644
--- a/libcxx/include/module.modulemap
+++ b/libcxx/include/module.modulemap
@@ -735,6 +735,10 @@ module std [system] {
   module variant {
     header "variant"
     export *
+
+    module __variant {
+      module monostate { header "__variant/monostate.h" }
+    }
   }
   module vector {
     header "vector"
diff --git a/libcxx/include/variant b/libcxx/include/variant
index 2145700e5a68..08b64612d133 100644
--- a/libcxx/include/variant
+++ b/libcxx/include/variant
@@ -202,6 +202,7 @@ namespace std {
 #include <__availability>
 #include <__config>
 #include <__utility/forward.h>
+#include <__variant/monostate.h>
 #include <__tuple>
 #include <array>
 #include <compare>
@@ -1703,26 +1704,6 @@ inline _LIBCPP_INLINE_VISIBILITY
 }
 #endif
 
-struct _LIBCPP_TEMPLATE_VIS monostate {};
-
-inline _LIBCPP_INLINE_VISIBILITY
-constexpr bool operator<(monostate, monostate) noexcept { return false; }
-
-inline _LIBCPP_INLINE_VISIBILITY
-constexpr bool operator>(monostate, monostate) noexcept { return false; }
-
-inline _LIBCPP_INLINE_VISIBILITY
-constexpr bool operator<=(monostate, monostate) noexcept { return true; }
-
-inline _LIBCPP_INLINE_VISIBILITY
-constexpr bool operator>=(monostate, monostate) noexcept { return true; }
-
-inline _LIBCPP_INLINE_VISIBILITY
-constexpr bool operator==(monostate, monostate) noexcept { return true; }
-
-inline _LIBCPP_INLINE_VISIBILITY
-constexpr bool operator!=(monostate, monostate) noexcept { return false; }
-
 template <class... _Types>
 inline _LIBCPP_INLINE_VISIBILITY
 auto swap(variant<_Types...>& __lhs,
@@ -1755,17 +1736,6 @@ struct _LIBCPP_TEMPLATE_VIS hash<
   }
 };
 
-template <>
-struct _LIBCPP_TEMPLATE_VIS hash<monostate> {
-  using argument_type = monostate;
-  using result_type = size_t;
-
-  inline _LIBCPP_INLINE_VISIBILITY
-  result_type operator()(const argument_type&) const _NOEXCEPT {
-    return 66740831; // return a fundamentally attractive random value.
-  }
-};
-
 #endif // _LIBCPP_STD_VER > 14
 
 _LIBCPP_END_NAMESPACE_STD