Adding a number format seems to break Excel reading the XLSX file

[fchorney]

I've been trying to figure out how to add number formats to my xlsx files and I seem to be hitting a road block here.

using XLSX

sheet_name = "test_sheet"

xf = XLSX.open_empty_template(sheet_name)
sheet = xf[sheet_name]
wb = XLSX.get_workbook(xf)

# Create a font style
fontattr = XLSX.FontAttribute["b", "name" => ("val" => "Calibri"), "sz" => ("val" => "12")]
boldfont = XLSX.styles_add_font(wb, fontattr)
boldstyle = XLSX.styles_add_cell_xf(
    wb,
    Dict("applyFont" => "true", "fontId" => "$boldfont"),
)

# This works fine if you open it up in Excel
sheet["A1"] = XLSX.CellValue("This is Bold", boldstyle)

XLSX.writexlsx("./numfmt_issue_working.xlsx", xf)

# Create a number format style
datefmt = XLSX.styles_add_numFmt(wb, "YYYYMMDD")
datestyle = XLSX.styles_add_cell_xf(
    wb,
    Dict("applyNumberFormat" => "1", "numFmtId" => "$datefmt"),
)

# This results in an error when Excel tries to read the file
sheet["A2"] = XLSX.CellValue(42332, datestyle)

XLSX.writexlsx("./numfmt_issue_broken.xlsx", xf)

If you run that snippet it will generate two files. Once the numFmt gets added to the workbook it seems to break compatibility with Excel.

Using Excel for Mac v16.29

[fchorney]

After a bunch of digging, it looks like the <numFmts><numFmts/> tag needs to appear in the xl/styles.xml file before it's referenced in the <cellXfs></cellXfs> block, or else Excel throws a fit about it. I'll write a fix and submit it in a bit.