[libcxx-commits] [libcxx] [libc++][chrono] Loads tzdata.zi in tzdb. (PR #74928)

[Louis Dionne via libcxx-commits]

================
@@ -0,0 +1,74 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+// For information see https://libcxx.llvm.org/DesignDocs/TimeZone.html
+
+#ifndef _LIBCPP___CHRONO_TIME_ZONE_H
+#define _LIBCPP___CHRONO_TIME_ZONE_H
+
+#include <version>
+// Enable the contents of the header only when libc++ was built with experimental features enabled.
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_TZDB)
+
+#  include <__compare/strong_order.h>
+#  include <__config>
+#  include <__memory/unique_ptr.h>
+#  include <string_view>
+
+#  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 >= 20 && !defined(_LIBCPP_HAS_NO_TIME_ZONE_DATABASE) && !defined(_LIBCPP_HAS_NO_FILESYSTEM) &&   \
+      !defined(_LIBCPP_HAS_NO_LOCALIZATION)
+
+namespace chrono {
+
+class _LIBCPP_AVAILABILITY_TZDB time_zone {
+public:
+  class __impl; // public so it can be used by make_unique.
+  _LIBCPP_NODISCARD_EXT _LIBCPP_EXPORTED_FROM_ABI explicit time_zone(unique_ptr<__impl>&& __p);
----------------
ldionne wrote:

I would avoid exporting a public constructor like this from the dylib, since that ties our API to our ABI in a really tight way. Instead, I would do this

```c++
// in the header
class time_zone {
private:
  _LIBCPP_HIDE_FROM_ABI explicit time_zone(unique_ptr<__impl>&& __p) : __impl_(std::move(__p)) { }

public:
  _LIBCPP_HIDE_FROM_ABI static time_zone __create(...); // declare only, don't define

  // ...
};

// in the dylib
time_zone time_zone::__create(...) { ... }
```

https://github.com/llvm/llvm-project/pull/74928