feat: Add number format 55 (Kor FMT, yyyy/mm/dd)

[9ssi7]

When I tried to format dates today, I saw that it was only formatted in dd-mm-yy format. After doing some research, I realized that Microsoft had support for this See Office Standarts, but it was omitted in this package.

The standard defines built-in format ID 14: "mm-dd-yy"; 22: "m/d/yy h:mm"; 37: "#,##0 ;(#,##0)"; 38: "#,##0 ;[Red]"; 39: "#,##0.00;(#,##0.00)"; 40: "#,##0.00;[Red]"; 47: "mmss.0"; KOR fmt 55: "yyyy-mm-dd".

Excel defines built-in format ID
14: "m/d/yyyy"
22: "m/d/yyyy h:mm"
37: "#,##0_);(#,##0)"
38: "#,##0_);[Red]"
39: "#,##0.00_);(#,##0.00)"
40: "#,##0.00_);[Red]"
47: "mm:ss.0"
55: "yyyy/mm/dd"

the area that will contain the change in question: https://github.com/tealeg/xlsx/blob/master/xmlStyle.go#L59

Is there a particular reason why it wasn't added?

[github-actions]

Stale issue message

[tealeg]

I'm pretty sure it was just an oversight. Adding it shouldn't be a hassle.

[benedictjohannes]

@9ssi7 since you have identified the issue and this has triaged, would you help with a PR maybe?

[benedictjohannes]

xlsx/xmlStyle.go

Line 27 in 3476977

var builtInNumFmt = map[int]string{

@tealeg @9ssi7 I looked around and found that more default number formats (including format no 55 discussed here) are language specific in exceljs, although number format 55 for zh-cn and zh-tw.

What do you think of language-specific number format? Seems convoluted to me 😖

[tealeg]

@benedictjohannes I think that would require some work to implement correctly.

I've considered for a while that it might be a mistake to have the library set up things like this. In some theoretical rewrite it would be simpler to force all interactions to start from an existing document and have these predefined things just be provided.