Some combination of keyed blocks and binding breaks array looping

[TehShrike]

Reproduction: https://svelte.technology/repl?version=1.26.0&gist=59c36b2a892a2e3be0d6b1441f5971f5

When the number is increased, on every other change, only the first two (after the reverse) elements are displayed.

Like the note in the repl says, if you remove any one of bind:top="idToTop[object.id]", position="{{object.id}}", or .reverse(), the issue doesn't happen.

[TehShrike]

Beyond that, here's the case I was actually trying to work towards, where the index/position in the array is passed in to the child component: https://svelte.technology/repl?version=1.26.0&gist=8e6a7f22a5813d146e2fa04d21285fd6

With the added this.observe('position') in the child, It produces actual console errors :-D

[TehShrike]

It looks like #728 only addresses the issue in that original repl link - should I just plan on this issue being closed and opening a new issue if the second repl still has issues after that patch is released?

[Rich-Harris]

@TehShrike will look into the second one separately. If we can fix both in one release, probably no need to raise a second issue

[Rich-Harris]

On second thoughts, this might warrant a separate issue. I've been poking around for a while and it's... complicated. Not currently sure what the best solution is. Have opened #730.