[gtk/gtk-2-24: 1/2] calendar: Use the new "%OB" format if supported

[Matthias Clasen <matthiasc src gnome org>]

commit 2ea743ab466703091a44a74e1a4ac7db983c0bca
Author: Rafal Luzynski <digitalfreak lingonborough com>
Date:   Sat Feb 10 14:07:56 2018 +0100

    calendar: Use the new "%OB" format if supported
    
    Due to the recent changes introduced in glibc 2.27 "%OB" is the
    correct format to obtain a month name as used in the calendar
    header.  The same rule has been working in BSD family (including
    OS X) since 1990s.  This simple hack checks whether "%OB" is supported
    at runtime and uses it if it is, falls back to the old "%B" otherwise.
    
    Closes: #9

 gtk/gtkcalendar.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)
---
diff --git a/gtk/gtkcalendar.c b/gtk/gtkcalendar.c
index 2dd68d6394..28baba16f1 100644
--- a/gtk/gtkcalendar.c
+++ b/gtk/gtkcalendar.c
@@ -689,6 +689,7 @@ gtk_calendar_init (GtkCalendar *calendar)
 #ifdef G_OS_WIN32
   wchar_t wbuffer[100];
 #else
+  static const char *month_format = NULL;
   char buffer[255];
   time_t tmp_time;
 #endif
@@ -714,7 +715,7 @@ gtk_calendar_init (GtkCalendar *calendar)
       {
 #ifndef G_OS_WIN32
        tmp_time= (i+3)*86400;
-       strftime ( buffer, sizeof (buffer), "%a", gmtime (&tmp_time));
+       strftime (buffer, sizeof (buffer), "%a", gmtime (&tmp_time));
        default_abbreviated_dayname[i] = g_locale_to_utf8 (buffer, -1, NULL, NULL, NULL);
 #else
        if (!GetLocaleInfoW (GetThreadLocale (), LOCALE_SABBREVDAYNAME1 + (i+6)%7,
@@ -730,7 +731,21 @@ gtk_calendar_init (GtkCalendar *calendar)
       {
 #ifndef G_OS_WIN32
        tmp_time=i*2764800;
-       strftime ( buffer, sizeof (buffer), "%B", gmtime (&tmp_time));
+       if (G_UNLIKELY (month_format == NULL))
+         {
+           buffer[0] = '\0';
+           month_format = "%OB";
+           strftime (buffer, sizeof (buffer), month_format, gmtime (&tmp_time));
+           /* "%OB" is not supported in Linux with glibc < 2.27  */
+           if (!strcmp (buffer, "%OB") || !strcmp (buffer, "OB") || !strcmp (buffer, ""))
+             {
+               month_format = "%B";
+               strftime (buffer, sizeof (buffer), month_format, gmtime (&tmp_time));
+             }
+         }
+       else
+         strftime (buffer, sizeof (buffer), month_format, gmtime (&tmp_time));
+
        default_monthname[i] = g_locale_to_utf8 (buffer, -1, NULL, NULL, NULL);
 #else
        if (!GetLocaleInfoW (GetThreadLocale (), LOCALE_SMONTHNAME1 + i,