show warning when using x-for without :key

[slaide]

the x-for docs say that It is important to specify unique keys for each x-for iteration if you are going to be re-ordering items. Without dynamic keys, Alpine may have a hard time keeping track of what re-orders and will cause odd side-effects..

I believe that behaviour that may cause odd side-effects (tracking that down just took me over an hour, hence this request) should not be the default, or at least not without a notice of some kind. #1639 to me indicates that improper :key usage should at least entail a warning, and will cause odd side-effects seems high stakes enough.

(Also, that note only mentions changing the order of the list, not changing the contents of the list as a more general statement, which seems like weird wording.)

[ekwoka]

Without :key the index is used by default.

The "odd side effects" is related to how, if you remove an item in the middle of the list, instead of removing that element (and any nested components) corresponding with that item from the dom, it will instead remove the last element, and change the ones between that item and the end to refer to new items, which may maintain incorrect nested state.

It might also be totally fine for a lot of cases.

Maybe it should include a warning, not totally sure. Too many warnings is its own issue in bloating package size...

[slaide]

ah, Without :key the index is used by default. makes this a lot clearer. that should really be in the documentation. (there is currently no mention what the 'default' :key is)

[ekwoka]

dang, I thought there was