1 files changed, 71 insertions, 0 deletions
diff --git a/libcxx/include/__format/format_args.h b/libcxx/include/__format/format_args.h
new file mode 100644
index 000000000000..0a26b95d1b47
--- /dev/null
+++ b/libcxx/include/__format/format_args.h
@@ -0,0 +1,71 @@
+// -*- 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___FORMAT_FORMAT_ARGS_H
+#define _LIBCPP___FORMAT_FORMAT_ARGS_H
+
+#include <__availability>
+#include <__config>
+#include <__format/format_fwd.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 > 17
+
+// TODO FMT Remove this once we require compilers with proper C++20 support.
+// If the compiler has no concepts support, the format header will be disabled.
+// Without concepts support enable_if needs to be used and that too much effort
+// to support compilers with partial C++20 support.
+#if !defined(_LIBCPP_HAS_NO_CONCEPTS)
+
+template <class _Context>
+class _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT basic_format_args {
+public:
+  // TODO FMT Implement [format.args]/5
+  // [Note 1: Implementations are encouraged to optimize the representation of
+  // basic_format_args for small number of formatting arguments by storing
+  // indices of type alternatives separately from values and packing the
+  // former. - end note]
+  // Note: Change  __format_arg_store to use a built-in array.
+  _LIBCPP_HIDE_FROM_ABI basic_format_args() noexcept = default;
+
+  template <class... _Args>
+  _LIBCPP_HIDE_FROM_ABI basic_format_args(
+      const __format_arg_store<_Context, _Args...>& __store) noexcept
+      : __size_(sizeof...(_Args)), __data_(__store.__args.data()) {}
+
+  _LIBCPP_HIDE_FROM_ABI
+  basic_format_arg<_Context> get(size_t __id) const noexcept {
+    return __id < __size_ ? __data_[__id] : basic_format_arg<_Context>{};
+  }
+
+  _LIBCPP_HIDE_FROM_ABI size_t __size() const noexcept { return __size_; }
+
+private:
+  size_t __size_{0};
+  const basic_format_arg<_Context>* __data_{nullptr};
+};
+
+#endif // !defined(_LIBCPP_HAS_NO_CONCEPTS)
+
+#endif //_LIBCPP_STD_VER > 17
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___FORMAT_FORMAT_ARGS_H