The calendar that pops up when one clicks the clock widget shows the week number of the last week in December 2020 as week 1. This is wrong. It should be week 53 (just like for December 2015, which *is* correctly displayed). Currently both the *last week* of 2020 and the *first week* of 2021 is shown as week 1.

Reproducible: Always

Steps to Reproduce:
1. Click the clock icon to show the calendar.
2. Click the current month name to zoom out and then the year number to zoom out further.
3. Click 2020 and the December.

Actual Results:  
The last week of December 2020 is shown as having week number 1.

Expected Results:  
The last week of December 2020 should be shown as having week number 53.

This problem may occur for other dates too; I have not done any extensive tests.

Note that having 1 as the week number for the week with the last day(s) of a year is not *necessarily* wrong. For example, the week number for this ‘last week’ is 1 for 2019, 53 for 2020 and 52 for 2021. (KDE displays the correct week number for 2019 and 2021.)

Information on calculation of the correct week numbers can be found at https://en.wikipedia.org/wiki/ISO_week_date

The correct calendar for 2020 can be seen at http://www.timeanddate.com/calendar/?year=2020

Or one may just use the command-line ‘cal’ utility included by default in most Linux distros. Here’s the command for showing December 2020 and January 2021:

cal -n2 -w 12 2020