Wrong interpretation of extra clause in ModelAdmin with new admin UI

[Florian Apolloner]

In the current admin you can specify max_num and extra for inlines. Before r12297 this meant that you would get the current data from the database + extra as long as it stays below max_num. If you were still below max_num you had to save the page to get extra new fields (this could be repeated until you reached the limit). This behaviour is currently implemented with the js too; but I think (as js is a usability enchancement) you should be able to add as many rows until you reach max_num not TOTAL-FORMS (which is rows+extra while <= max_num). To get this working I guess we would need to pass max_num to the js so it can decide when to stop.

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An alternate description from #12704:

The new javascript-enabled admin UI appears have an unusual interpretation of the 'extra' clause on a ModelAdmin?.

The current code interprets 'extra = N' as "allow the user to add no more than N extra rows. The user must press (+ add another XXX) to add the first inline.

I would have thought the interpretation would have been "instantiate the form with with N empty extra rows". The task of constraining the number of allowed inlines is the job of the 'max_num' clause.

The admin UI should always show N blank inputs (for extra = N), as long as that wouldn't exceed the max_num. The user should be able to fill in up to N inlines before needing to press the (+ add another) button.

If I'm incorrect, then the second failing test reported by #12703 needs to be fixed by accounting for the 5 fields (and missing default date) that are no longer on the form.

[Russell Keith-Magee]

#12704 was a duplicate. Updated ticket title to be more explicit.