gdatetime: Add support for %E modifier to g_date_time_format()

The `%E` modifier causes dates to be formatted using an alternative era representation for years. This doesn’t do anything for most dates, but in locales such as Thai and Japanese it causes years to be printed using era names. In Thai, this means the Thai solar calendar (https://en.wikipedia.org/wiki/Thai_solar_calendar). In Japanese, this means Japanese era names (https://en.wikipedia.org/wiki/Japanese_era_name). The `%E` modifier syntax follows what’s supported in glibc — see nl_langinfo(3). Supporting this is quite involved, as it means loading the `ERA` description from libc and parsing it. Unit tests are included. Signed-off-by: Philip Withnall <philip@tecnocode.co.uk> Fixes: #3119
2025-08-21 16:38:54 +02:00 · 2023-10-18 15:50:57 +01:00
parent ded4976337
commit df4aea7620
11 changed files with 784 additions and 14 deletions
--- a/glib/gdatetime.c
+++ b/glib/gdatetime.c
@@ -69,6 +69,7 @@
 #include "gconvert.h"
 #include "gconvertprivate.h"
 #include "gdatetime.h"
+#include "gdatetime-private.h"
 #include "gfileutils.h"
 #include "ghash.h"
 #include "glibintl.h"
@@ -162,8 +163,11 @@ static const guint16 days_in_year[2][13] =
 #define GET_AMPM_IS_LOCALE TRUE

 #define PREFERRED_DATE_TIME_FMT nl_langinfo (D_T_FMT)
+#define PREFERRED_ERA_DATE_TIME_FMT nl_langinfo (ERA_D_T_FMT)
 #define PREFERRED_DATE_FMT nl_langinfo (D_FMT)
+#define PREFERRED_ERA_DATE_FMT nl_langinfo (ERA_D_FMT)
 #define PREFERRED_TIME_FMT nl_langinfo (T_FMT)
+#define PREFERRED_ERA_TIME_FMT nl_langinfo (ERA_T_FMT)
 #define PREFERRED_12HR_TIME_FMT nl_langinfo (T_FMT_AMPM)

 static const gint weekday_item[2][7] =
@@ -187,6 +191,10 @@ static const gint month_item[2][12] =
 #define MONTH_FULL(d) nl_langinfo (month_item[1][g_date_time_get_month (d) - 1])
 #define MONTH_FULL_IS_LOCALE TRUE

+#define ERA_DESCRIPTION nl_langinfo (ERA)
+#define ERA_DESCRIPTION_IS_LOCALE TRUE
+#define ERA_DESCRIPTION_N_SEGMENTS (int) (gintptr) nl_langinfo (_NL_TIME_ERA_NUM_ENTRIES)
+
 #else

 #define GET_AMPM(d)          (get_fallback_ampm (g_date_time_get_hour (d)))
@@ -194,12 +202,15 @@ static const gint month_item[2][12] =

 /* Translators: this is the preferred format for expressing the date and the time */
 #define PREFERRED_DATE_TIME_FMT C_("GDateTime", "%a %b %e %H:%M:%S %Y")
+#define PREFERRED_ERA_DATE_TIME_FMT PREFERRED_DATE_TIME_FMT

 /* Translators: this is the preferred format for expressing the date */
 #define PREFERRED_DATE_FMT C_("GDateTime", "%m/%d/%y")
+#define PREFERRED_ERA_DATE_FMT PREFERRED_DATE_FMT

 /* Translators: this is the preferred format for expressing the time */
 #define PREFERRED_TIME_FMT C_("GDateTime", "%H:%M:%S")
+#define PREFERRED_ERA_TIME_FMT PREFERRED_TIME_FMT

 /* Translators: this is the preferred format for expressing 12 hour time */
 #define PREFERRED_12HR_TIME_FMT C_("GDateTime", "%I:%M:%S %p")
@@ -219,6 +230,10 @@ static const gint month_item[2][12] =
 #define MONTH_FULL(d)         (get_month_name_standalone (g_date_time_get_month (d)))
 #define MONTH_FULL_IS_LOCALE  FALSE

+#define ERA_DESCRIPTION NULL
+#define ERA_DESCRIPTION_IS_LOCALE FALSE
+#define ERA_DESCRIPTION_N_SEGMENTS 0
+
 static const gchar *
 get_month_name_standalone (gint month)
 {
@@ -2865,6 +2880,131 @@ initialize_alt_digits (void)
 }
 #endif /* HAVE_LANGINFO_OUTDIGIT */

+/* Look up the era which contains @datetime, in the ERA description from libc
+ * which corresponds to the currently set LC_TIME locale. The ERA is parsed and
+ * cached the first time this function is called (or when LC_TIME changes).
+ * See nl_langinfo(3).
+ *
+ * The return value is (transfer full). */
+static GEraDescriptionSegment *
+date_time_lookup_era (GDateTime *datetime,
+                      gboolean   locale_is_utf8)
+{
+  static GMutex era_mutex;
+  static GPtrArray *static_era_description = NULL;  /* (mutex era_mutex) (element-type GEraDescriptionSegment) */
+  static const char *static_era_description_locale = NULL;  /* (mutex era_mutex) */
+  const char *current_lc_time = setlocale (LC_TIME, NULL);
+  GPtrArray *local_era_description;  /* (element-type GEraDescriptionSegment) */
+  GEraDate datetime_date;
+
+  g_mutex_lock (&era_mutex);
+
+  if (static_era_description_locale != current_lc_time)
+    {
+      const char *era_description_str;
+      size_t era_description_str_len;
+      char *tmp = NULL;
+
+      era_description_str = ERA_DESCRIPTION;
+      if (era_description_str != NULL)
+        {
+          /* FIXME: glibc 2.37 seems to return the era segments nul-separated rather
+           * than semicolon-separated (which is what nl_langinfo(3) specifies).
+           * Fix that up before sending it to the parsing code.
+           * See https://sourceware.org/bugzilla/show_bug.cgi?id=31030*/
+            {
+              /* Work out the length of the whole description string, regardless
+               * of whether it uses nuls or semicolons as separators. */
+              int n_entries = ERA_DESCRIPTION_N_SEGMENTS;
+              const char *s = era_description_str;
+
+              for (int i = 1; i < n_entries; i++)
+                {
+                  const char *next_semicolon = strchr (s, ';');
+                  const char *next_nul = strchr (s, '\0');
+
+                  if (next_semicolon != NULL && next_semicolon < next_nul)
+                    s = next_semicolon + 1;
+                  else
+                    s = next_nul + 1;
+                }
+
+              era_description_str_len = strlen (s) + (s - era_description_str);
+
+              /* Replace all the nuls with semicolons. */
+              era_description_str = tmp = g_memdup2 (era_description_str, era_description_str_len + 1);
+              s = era_description_str;
+
+              for (int i = 1; i < n_entries; i++)
+                {
+                  char *next_nul = strchr (s, '\0');
+
+                  if ((size_t) (next_nul - era_description_str) >= era_description_str_len)
+                    break;
+
+                  *next_nul = ';';
+                  s = next_nul + 1;
+                }
+            }
+
+          /* Convert from the LC_TIME encoding to UTF-8 if needed. */
+          if (!locale_is_utf8 && ERA_DESCRIPTION_IS_LOCALE)
+            {
+              char *tmp2 = NULL;
+              era_description_str = tmp2 = g_locale_to_utf8 (era_description_str, -1, NULL, NULL, NULL);
+              g_free (tmp);
+              tmp = g_steal_pointer (&tmp2);
+            }
+
+          g_clear_pointer (&static_era_description, g_ptr_array_unref);
+
+          if (era_description_str != NULL)
+            static_era_description = _g_era_description_parse (era_description_str);
+        }
+
+      if (static_era_description == NULL)
+        g_warning ("Could not parse ERA description: %s", era_description_str);
+
+      g_free (tmp);
+
+      static_era_description_locale = current_lc_time;
+    }
+
+  if (static_era_description == NULL)
+    {
+      g_mutex_unlock (&era_mutex);
+      return NULL;
+    }
+
+  local_era_description = g_ptr_array_ref (static_era_description);
+  g_mutex_unlock (&era_mutex);
+
+  /* Search through the eras and see if one matches. */
+  datetime_date.type = G_ERA_DATE_SET;
+  datetime_date.year = g_date_time_get_year (datetime);
+  datetime_date.month = g_date_time_get_month (datetime);
+  datetime_date.day = g_date_time_get_day_of_month (datetime);
+
+  for (unsigned int i = 0; i < local_era_description->len; i++)
+    {
+      GEraDescriptionSegment *segment = g_ptr_array_index (local_era_description, i);
+
+      if ((_g_era_date_compare (&segment->start_date, &datetime_date) <= 0 &&
+           _g_era_date_compare (&datetime_date, &segment->end_date) <= 0) ||
+          (_g_era_date_compare (&segment->end_date, &datetime_date) <= 0 &&
+           _g_era_date_compare (&datetime_date, &segment->start_date) <= 0))
+        {
+          /* @datetime is within this era segment. */
+          g_ptr_array_unref (local_era_description);
+          return _g_era_description_segment_ref (segment);
+        }
+    }
+
+  g_ptr_array_unref (local_era_description);
+
+  return NULL;
+}
+
 static void
 format_number (GString     *str,
               gboolean     use_alt_digits,
@@ -3043,6 +3183,7 @@ g_date_time_format_utf8 (GDateTime   *datetime,
  guint     colons;
  gunichar  c;
  gboolean  alt_digits = FALSE;
+  gboolean alt_era = FALSE;
  gboolean  pad_set = FALSE;
  gboolean mod_case = FALSE;
  gboolean  name_is_utf8;
@@ -3069,6 +3210,7 @@ g_date_time_format_utf8 (GDateTime   *datetime,

      colons = 0;
      alt_digits = FALSE;
+      alt_era = FALSE;
      pad_set = FALSE;
      mod_case = FALSE;

@@ -3129,14 +3271,31 @@ g_date_time_format_utf8 (GDateTime   *datetime,
 	  break;
 	case 'c':
 	  {
-            if (g_strcmp0 (PREFERRED_DATE_TIME_FMT, "") == 0)
+            const char *subformat = alt_era ? PREFERRED_ERA_DATE_TIME_FMT : PREFERRED_DATE_TIME_FMT;
+
+            /* Fallback */
+            if (alt_era && g_strcmp0 (subformat, "") == 0)
+              subformat = PREFERRED_DATE_TIME_FMT;
+
+            if (g_strcmp0 (subformat, "") == 0)
              return FALSE;
-            if (!g_date_time_format_locale (datetime, PREFERRED_DATE_TIME_FMT,
+            if (!g_date_time_format_locale (datetime, subformat,
                                            outstr, locale_is_utf8))
              return FALSE;
 	  }
 	  break;
 	case 'C':
+          if (alt_era)
+            {
+              GEraDescriptionSegment *era = date_time_lookup_era (datetime, locale_is_utf8);
+              if (era != NULL)
+                {
+                  g_string_append (outstr, era->era_name);
+                  _g_era_description_segment_unref (era);
+                  break;
+                }
+            }
+
 	  format_number (outstr, alt_digits, pad_set ? pad : "0", 2,
 			 g_date_time_get_year (datetime) / 100);
 	  break;
@@ -3214,6 +3373,9 @@ g_date_time_format_utf8 (GDateTime   *datetime,
 	case 'O':
 	  alt_digits = TRUE;
 	  goto next_mod;
+        case 'E':
+          alt_era = TRUE;
+          goto next_mod;
 	case 'p':
          if (!format_ampm (datetime, outstr, locale_is_utf8,
                            mod_case && g_strcmp0 (mod, "#") == 0 ? FALSE
@@ -3270,29 +3432,78 @@ g_date_time_format_utf8 (GDateTime   *datetime,
 	  break;
 	case 'x':
 	  {
-            if (g_strcmp0 (PREFERRED_DATE_FMT, "") == 0)
+            const char *subformat = alt_era ? PREFERRED_ERA_DATE_FMT : PREFERRED_DATE_FMT;
+
+            /* Fallback */
+            if (alt_era && g_strcmp0 (subformat, "") == 0)
+              subformat = PREFERRED_DATE_FMT;
+
+            if (g_strcmp0 (subformat, "") == 0)
              return FALSE;
-	    if (!g_date_time_format_locale (datetime, PREFERRED_DATE_FMT,
+	    if (!g_date_time_format_locale (datetime, subformat,
 					    outstr, locale_is_utf8))
 	      return FALSE;
 	  }
 	  break;
 	case 'X':
 	  {
-            if (g_strcmp0 (PREFERRED_TIME_FMT, "") == 0)
+            const char *subformat = alt_era ? PREFERRED_ERA_TIME_FMT : PREFERRED_TIME_FMT;
+
+            /* Fallback */
+            if (alt_era && g_strcmp0 (subformat, "") == 0)
+              subformat = PREFERRED_TIME_FMT;
+
+            if (g_strcmp0 (subformat, "") == 0)
              return FALSE;
-	    if (!g_date_time_format_locale (datetime, PREFERRED_TIME_FMT,
+	    if (!g_date_time_format_locale (datetime, subformat,
 					    outstr, locale_is_utf8))
 	      return FALSE;
 	  }
 	  break;
 	case 'y':
-	  format_number (outstr, alt_digits, pad_set ? pad : "0", 2,
-			 g_date_time_get_year (datetime) % 100);
+          if (alt_era)
+            {
+              GEraDescriptionSegment *era = date_time_lookup_era (datetime, locale_is_utf8);
+              if (era != NULL)
+                {
+                  int delta = g_date_time_get_year (datetime) - era->start_date.year;
+
+                  /* Both these years are in the Gregorian calendar (CE/BCE),
+                   * which has no year zero. So take one from the delta if they
+                   * cross across where year zero would be. */
+                  if ((g_date_time_get_year (datetime) < 0) != (era->start_date.year < 0))
+                    delta -= 1;
+
+                  format_number (outstr, alt_digits, pad_set ? pad : "0", 2,
+                                 era->offset + delta * era->direction_multiplier);
+                  _g_era_description_segment_unref (era);
+                  break;
+                }
+            }
+
+          format_number (outstr, alt_digits, pad_set ? pad : "0", 2,
+                         g_date_time_get_year (datetime) % 100);
 	  break;
 	case 'Y':
-	  format_number (outstr, alt_digits, 0, 0,
-			 g_date_time_get_year (datetime));
+          if (alt_era)
+            {
+              GEraDescriptionSegment *era = date_time_lookup_era (datetime, locale_is_utf8);
+              if (era != NULL)
+                {
+                  if (!g_date_time_format_utf8 (datetime, era->era_format,
+                                                outstr, locale_is_utf8))
+                    {
+                      _g_era_description_segment_unref (era);
+                      return FALSE;
+                    }
+
+                  _g_era_description_segment_unref (era);
+                  break;
+                }
+            }
+
+          format_number (outstr, alt_digits, 0, 0,
+                         g_date_time_get_year (datetime));
 	  break;
 	case 'z':
 	  {
@@ -3461,6 +3672,22 @@ g_date_time_format_utf8 (GDateTime   *datetime,
 * `strftime()` extension expected to be added to the future POSIX specification,
 * `%Ob` and `%Oh` are GNU `strftime()` extensions. Since: 2.56
 *
+ * Since GLib 2.80, when `E` is used with `%c`, `%C`, `%x`, `%X`, `%y` or `%Y`,
+ * the date is formatted using an alternate era representation specific to the
+ * locale. This is typically used for the Thai solar calendar or Japanese era
+ * names, for example.
+ *
+ * - `%Ec`: the preferred date and time representation for the current locale,
+ *   using the alternate era representation
+ * - `%EC`: the name of the era
+ * - `%Ex`: the preferred date representation for the current locale without
+ *   the time, using the alternate era representation
+ * - `%EX`: the preferred time representation for the current locale without
+ *   the date, using the alternate era representation
+ * - `%Ey`: the year since the beginning of the era denoted by the `%EC`
+ *   specifier
+ * - `%EY`: the full alternative year representation
+ *
 * Returns: (transfer full) (nullable): a newly allocated string formatted to
 *    the requested format or %NULL in the case that there was an error (such
 *    as a format specifier not being supported in the current locale). The