[PATCH] libstdc++: Search for tzdata on Windows (msys)

[Björn Schäpers]

From: Björn Schäpers <bjo...@hazardy.de>

Windows does not provide a tzdata.zi, but msys does. Use this, if
available, instead of the embedded (and possibly outdated) database.

libstdc++-v3/Changelog:

        Use msys provided time zone information.

        * src/c++20/tzdb.cc (zoneinfo_file): On Windows look relative
        from the DLL path for the time zone information.

Signed-off-by: Björn Schäpers <bjo...@hazardy.de>
---
 libstdc++-v3/src/c++20/tzdb.cc | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/libstdc++-v3/src/c++20/tzdb.cc b/libstdc++-v3/src/c++20/tzdb.cc
index 6e244dc656d..ef81ba7ff80 100644
--- a/libstdc++-v3/src/c++20/tzdb.cc
+++ b/libstdc++-v3/src/c++20/tzdb.cc
@@ -44,6 +44,11 @@
 # include <cstdlib>   // getenv
 #endif
 
+#if _GLIBCXX_HAVE_WINDOWS_H
+# define WIN32_LEAN_AND_MEAN
+# include <windows.h>
+#endif
+
 #if defined __GTHREADS && ATOMIC_POINTER_LOCK_FREE == 2
 # define USE_ATOMIC_LIST_HEAD 1
 // TODO benchmark atomic<shared_ptr<>> vs mutex.
@@ -1144,6 +1149,26 @@ namespace std::chrono
 #ifdef _GLIBCXX_ZONEINFO_DIR
       else
        path = _GLIBCXX_ZONEINFO_DIR;
+#endif
+#ifdef _GLIBCXX_HAVE_WINDOWS_H
+      if (path.empty () || path == "yes")
+       {
+         char dll_path[MAX_PATH];
+         if (GetModuleFileNameA (nullptr, dll_path, MAX_PATH) != 0)
+           {
+             string_view dll_path_view = dll_path;
+             auto pos = dll_path_view.find_last_of ('\\');
+             dll_path_view = dll_path_view.substr (0, pos);
+             if (dll_path_view.ends_with ("\\bin"))
+               {
+                 constexpr string_view remaining_path = "share\\zoneinfo";
+                 dll_path_view.remove_suffix (3); // Remove bin
+                 path.resize (dll_path_view.size () + remaining_path.size ());
+                 auto iter = ranges::copy (dll_path_view, path.begin ()).out;
+                 ranges::copy (remaining_path, iter);
+               }
+           }
+       }
 #endif
       if (!path.empty())
        path.append(filename);
-- 
2.50.0