Validate multiple additions/subtractions to GDateTime
As per !1622 (comment 893144) it looks like it’s possible to overflow a GDateTime
at the moment by calling (for example) g_date_time_add_years()
multiple times:
dt2 = g_date_time_add_years (dt1, 9999);
dt3 = g_date_time_add_years (dt2, 9999);
…
This should be validated. Same for add_months()
etc.