time: get timezones from tzdata.zi

The zone1970.tab file doesn't include any timezone 'aliases'. Instead
of parsing it, parse the tzdata.zi file which does include all zones
as well as aliases.

This keeps the parsing function for zone1970.tab as a fallback in case
the tzdata.zi file isn't found.

src/basic/time-util.c

@@ -1303,13 +1303,69 @@ static int get_timezones_from_zone1970_tab(char ***ret) {
         return 0;
 }
 
+static int get_timezones_from_tzdata_zi(char ***ret) {
+        _cleanup_fclose_ FILE *f = NULL;
+        _cleanup_strv_free_ char **zones = NULL;
+        int r;
+
+        f = fopen("/usr/share/zoneinfo/tzdata.zi", "re");
+        if (!f)
+                return -errno;
+
+        for (;;) {
+                _cleanup_free_ char *line = NULL, *type = NULL, *f1 = NULL, *f2 = NULL;
+
+                r = read_line(f, LONG_LINE_MAX, &line);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+
+                const char *p = line;
+
+                /* The only lines we care about are Zone and Link lines.
+                 * Zone line format is:
+                 * 'Zone' 'timezone' ...
+                 * Link line format is:
+                 * 'Link' 'target' 'alias'
+                 * See 'man zic' for more detail. */
+                r = extract_many_words(&p, NULL, 0, &type, &f1, &f2, NULL);
+                if (r < 0)
+                        continue;
+
+                char *tz;
+                if (*type == 'Z' || *type == 'z')
+                        /* Zone lines have timezone in field 1. */
+                        tz = f1;
+                else if (*type == 'L' || *type == 'l')
+                        /* Link lines have timezone in field 2. */
+                        tz = f2;
+                else
+                        /* Not a line we care about. */
+                        continue;
+
+                r = strv_extend(&zones, tz);
+                if (r < 0)
+                        return r;
+        }
+
+        *ret = TAKE_PTR(zones);
+        return 0;
+}
+
 int get_timezones(char ***ret) {
         _cleanup_strv_free_ char **zones = NULL;
         int r;
 
         assert(ret);
 
+        r = get_timezones_from_tzdata_zi(&zones);
+        if (r == -ENOENT) {
+                log_debug_errno(r, "Could not get timezone data from tzdata.zi, using zone1970.tab: %m");
                 r = get_timezones_from_zone1970_tab(&zones);
+                if (r == -ENOENT)
+                        log_debug_errno(r, "Could not get timezone data from zone1970.tab, using UTC: %m");
+        }
         if (r < 0 && r != -ENOENT)
                 return r;