Warn when unnamed groups are uploaded via XLSForm

[jnm]

Edit: maybe "reject" is a better approach than "warn".

Especially unnamed, unlabeled groups. These will have newly auto-generated names assigned each time the XLSForm is re-uploaded. kobotoolbox/formpack#206 can be triggered by this, but even when that is fixed, groups whose names change with every version are going to create a mess in the exports (likely new columns for each group [1] [2] [3]).

Internal discussion: https://chat.kobotoolbox.org/#narrow/stream/4-KoBo-Dev/topic/Export.20failure.20on.20multiple.20versions/near/21509

How to reproduce:

1. create an XLSForm with a repeating group that has both no name and no label unnamed and unlabeled repeat.xlsx
2. upload it to KPI
3. look at the form json; see (e.g.) begin_repeat_oqAkea1ft
4. upload the same XLSForm again
5. refresh the json
6. see (e.g.) begin_repeat_B8cPyAGB7; notice it's different than the name seen in (3)

Workaround for when this happens (or even when people deliberately change group names): https://community.kobotoolbox.org/t/export-failed-error/13957. I'm unsure whether the workaround can be used in all cases.

[tinok]

👍
I feel that if someone uploads an incorrect XLSForm we should in the future reject it (with useful feedback), as we do for many kinds of errors; but importing an invalid form and silently adding / updating names goes in the area of editing someone's form.

[Kalyan-Lama]

@jnm, maybe this community post and the verification I made should be helpful:

https://community.kobotoolbox.org/t/export-data-failed/17583/14