The POSIX rule parser used by QTzTimeZonePrivate recklessly assumed that, if splitting the rule on a dot produced more than one part, it necessarily produced at least three. That's true for well-formed POSIX rules, but we should catch the case of malformed rules. Likewise, when calculating the dates of transitions, splitting the date rule on dots might produce too few fragments; and the fragments might not parse as valid numbers, or might be out of range for their respective fields in a date. Check all these cases, too. Added a test that crashed previously. Changed QTimeZone::offsetFromUtc() so that its "return zero on invalid" applies also to the case where the backend returns invalid, in support of this. Fixes: QTBUG-92808 Pick-to: 6.1 6.1.0 6.0 5.15 Change-Id: Ica383a7a987465483341bdef8dcfd42edb6b43d6 Reviewed-by: Andrei Golubev <andrei.golubev@qt.io> Reviewed-by: Thiago Macieira <thiago.macieira@intel.com> Reviewed-by: Robert Löhning <robert.loehning@qt.io>