Do we need indexes in lines?

[samlown]

Suddenly had a thought, maybe the "Index" or i field in Invoice lines is not very useful:

gobl/bill/line.go

Lines 15 to 16 in b8eb2ee

	// Line number inside the parent (calculated)
	Index int `json:"i" jsonschema:"title=Index" jsonschema_extras:"calculated=true"`

It's auto calculated as the index of the row in the array, plus one, so in reality adds very little value, and potentially adds noise.

[cavalle]

I suppose we could live without it, but I do see some value on having an attribute that indicates explicitly and
unequivocally the index of an invoice line. It also serves as an identifier of the line. And it's not an uncommon field in the invoicing domain (for example, DIAN's UBL expects consecutive IDs for each of their InvoiceLines).

I don't know if this field is causing trouble somewhere else but, based on my knowledge, my vote goes to keeping it.