[glib: 2/3] Fix the 6-days-until-the-end-of-the-month bug

[Emmanuele Bassi <ebassi src gnome org>]

commit da00779093f8c69b77b578795e8bec8e27f107d0
Author: Руслан Ижбулатов <lrn1986 gmail com>
Date:   Mon Oct 5 16:53:47 2020 +0000

    Fix the 6-days-until-the-end-of-the-month bug
    
    The addition causes the date to shift
    forward into 1st of the next month, because a 0-based offset
    is compared to be "more than" the days in the month instead of "more than
    or equal to".
    
    This is triggered by corner-cases where transition date is 6 days
    off the end of the month and our calculations put it at N+1th day of the
    month (where N is the number of days in the month). The subtraction should
    be triggered to move the date back a week, putting it 6 days off the end;
    for example, October 25 for CET DST transition; but due to incorrect comparison
    the date isn't shifted back, we add 31 days to October 1st and end up
    at November 1st).
    
    Fixes issue #2215.

 glib/gtimezone.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
---
diff --git a/glib/gtimezone.c b/glib/gtimezone.c
index ef67ec50b..0de5c92a3 100644
--- a/glib/gtimezone.c
+++ b/glib/gtimezone.c
@@ -1041,7 +1041,11 @@ find_relative_date (TimeZoneDate *buffer)
       /* week is 1 <= w <= 5, we need 0-based */
       days = 7 * (buffer->week - 1) + wday - first_wday;
 
-      while (days > days_in_month)
+      /* "days" is a 0-based offset from the 1st of the month.
+       * Adding days == days_in_month would bring us into the next month,
+       * hence the ">=" instead of just ">".
+       */
+      while (days >= days_in_month)
         days -= 7;
 
       g_date_add_days (&date, days);