[gnome-desktop/wip/fmuellner/lctime-format-strings] wall-clock: Use LC_TIME for strftime format string translations

[Florian Müllner <fmuellner src gnome org>]

commit 7ab5e379f57e09ee18b2209bfb96e28d21b5cbaa
Author: Florian Müllner <fmuellner gnome org>
Date:   Thu Oct 19 18:36:09 2017 +0200

    wall-clock: Use LC_TIME for strftime format string translations
    
    In order to handle the clock's various display setting correctly for
    different locales, we mark strftime format strings for translation.
    However those translations are looked up according to the locale
    defined by LC_MESSAGES, while the conversion characters themselves
    are resolved according to LC_TIME, with rather odd results when
    mixing locales.
    The correct solution would be to install translations for format
    strings in the LC_TIME catalogue and look them up with dcgettext(),
    but we don't have the infrastructure to do that easily. Work around
    this by adding a helper method that looks up a string in LC_MESSAGES
    using the locale defined by LC_TIME and use that to translate the
    format strings, which has the same result.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=789205

 libgnome-desktop/gnome-wall-clock.c | 59 +++++++++++++++++++++++++++----------
 1 file changed, 44 insertions(+), 15 deletions(-)
---
diff --git a/libgnome-desktop/gnome-wall-clock.c b/libgnome-desktop/gnome-wall-clock.c
index f92028cd..a5893021 100644
--- a/libgnome-desktop/gnome-wall-clock.c
+++ b/libgnome-desktop/gnome-wall-clock.c
@@ -24,6 +24,7 @@
 
 #include "config.h"
 
+#include <locale.h>
 #include <glib/gi18n-lib.h>
 
 #define GNOME_DESKTOP_USE_UNSTABLE_API
@@ -265,6 +266,31 @@ date_time_format (GDateTime *datetime,
        return ret;
 }
 
+/*
+ * Translate @str according to the locale defined by LC_TIME; unlike
+ * dcgettext(), the translation is still taken from the LC_MESSAGES
+ * catalogue and not the LC_TIME one.
+ */
+static const char *
+translate_time_format_string (const char *str)
+{
+  const char *locale = g_getenv ("LC_TIME");
+  const char *res;
+  char *sep;
+
+  if (locale)
+    setlocale (LC_MESSAGES, locale);
+
+  sep = strchr (str, '\004');
+  res = g_dpgettext (GETTEXT_PACKAGE, str, sep ? sep - str + 1 : 0);
+
+  setlocale (LC_MESSAGES, "");
+
+  return res;
+}
+
+#define T_(string) translate_time_format_string (string)
+
 /**
  * gnome_wall_clock_string_for_datetime:
  *
@@ -287,23 +313,24 @@ gnome_wall_clock_string_for_datetime (GnomeWallClock      *self,
                                /* Translators: This is the time format with full date
                                   plus day used in 24-hour mode. Please keep the under-
                                   score to separate the date from the time. */
-                               format_string = show_seconds ? _("%a %b %-e_%R:%S")
-                                       : _("%a %b %-e_%R");
+                               format_string = show_seconds ? T_(N_("%a %b %-e_%R:%S"))
+                                       : T_(N_("%a %b %-e_%R"));
                        else
                                /* Translators: This is the time format with full date
                                   used in 24-hour mode. Please keep the underscore to
                                   separate the date from the time. */
-                               format_string = show_seconds ? _("%b %-e_%R:%S")
-                                       : _("%b %-e_%R");
+                               format_string = show_seconds ? T_(N_("%b %-e_%R:%S"))
+                                       : T_(N_("%b %-e_%R"));
                } else if (show_weekday) {
                        /* Translators: This is the time format with day used
                           in 24-hour mode. */
-                       format_string = show_seconds ? _("%a %R:%S")
-                               : _("%a %R");
+                       format_string = show_seconds ? T_(N_("%a %R:%S"))
+                               : T_(N_("%a %R"));
                } else {
                        /* Translators: This is the time format without date used
                           in 24-hour mode. */
-                       format_string = show_seconds ? _("%R:%S") : _("%R");
+                       format_string = show_seconds ? T_(N_("%R:%S"))
+                                : T_(N_("%R"));
                }
        } else {
                if (show_full_date) {
@@ -311,30 +338,32 @@ gnome_wall_clock_string_for_datetime (GnomeWallClock      *self,
                                /* Translators: This is a time format with full date
                                   plus day used for AM/PM. Please keep the under-
                                   score to separate the date from the time. */
-                               format_string = show_seconds ? _("%a %b %-e_%l:%M:%S %p")
-                                       : _("%a %b %-e_%l:%M %p");
+                               format_string = show_seconds ? T_(N_("%a %b %-e_%l:%M:%S %p"))
+                                       : T_(N_("%a %b %-e_%l:%M %p"));
                        else
                                /* Translators: This is a time format with full date
                                   used for AM/PM. Please keep the underscore to
                                   separate the date from the time. */
-                               format_string = show_seconds ? _("%b %-e_%l:%M:%S %p")
-                                       : _("%b %-e_%l:%M %p");
+                               format_string = show_seconds ? T_(N_("%b %-e_%l:%M:%S %p"))
+                                       : T_(N_("%b %-e_%l:%M %p"));
                } else if (show_weekday) {
                        /* Translators: This is a time format with day used
                           for AM/PM. */
-                       format_string = show_seconds ? _("%a %l:%M:%S %p")
-                               : _("%a %l:%M %p");
+                       format_string = show_seconds ? T_(N_("%a %l:%M:%S %p"))
+                               : T_(N_("%a %l:%M %p"));
                } else {
                        /* Translators: This is a time format without date used
                           for AM/PM. */
-                       format_string = show_seconds ? _("%l:%M:%S %p")
-                               : _("%l:%M %p");
+                       format_string = show_seconds ? T_(N_("%l:%M:%S %p"))
+                               : T_(N_("%l:%M %p"));
                }
        }
 
        return date_time_format (now, format_string);
 }
 
+#undef T_
+
 static gboolean
 update_clock (gpointer data)
 {