Viewxls macro wrongly calculates the first week number of each year with the Excel WEEKNUM() function

Bug description

According to Excel documentation: https://support.office.com/en-us/article/WEEKNUM-function-e5c43a03-b4ab-426c-b411-b18c13c75340

The WEEKNUM() function in Excel will calculate the number of the week based on a provided date.

• Jan 1 is always Week 1
• The first Sunday encountered after Jan 1 is the beginning of Week 2

The bug is that the ViewXLS macro will erroneously calculate the days of the year before the first Saturday as Week 2.

Steps to reproduce

1. Download the attached example file: weeknumbers.xlsx
2. Upload to Confluence (I tested in Confluence 5.8.18)
3. Insert a ViewXLS macro (display name is "Excel Macro") to the page referencing the attachment
4. Note the discrepancies in the first few days of each year.

For example, Jan 7 2017 is the first Saturday of 2017. Jan 1 through Jan 6 should all be Week 1, but ViewXLS will show Week 2.

Workarounds

• This bug does not affect the new Files Preview experience introduced in Confluence 5.7. It is recommended to use that over the ViewXLS macro, which has been deprecated as of Confluence 5.9