Svelte 5 runtime crash inside each block

[gyzerok]

Describe the bug

In our crashlog system I can see the following error

Reproduction

Unfortunately I am unable to figure out what exactly is causing this. Will come back with repro if will catch it. But maybe someone from the maintainers could make a good guess out of the stack trace from the above.

Logs

No response

System Info

Svelte 5.2.7

Severity

annoyance

[trueadm]

We're going to need more information unfortunately – there could be many reasons why the above is happening. Does this occur on hydration or during updates? Are you using transitions/animations?

[gyzerok]

We are client-only, so no hydration for sure. Yes, we are using transitions and flip animation in various places

[trueadm]

Can you help narrow it down by removing some of the animations from the each blocks until the issue stops happening, that might make it easier to reproduce. Also are you moving around the DOM manually anywhere?

[gyzerok]

Haven't had any more crashes since. However there is one weird thing, that might have been connected. There was a call to derivedValue.reverse() in some place causing weird bug. Code roughly looked like this:

const list = $derived.by(() => ids.map(cache.get))

const handleEvent = () => {
  for (const item of list.reverse()) {
    // do stuff
  }
}

I dunno if this could be connected and I wasn't able to reproduce it still, but I am wondering if svelte should somehow error or crash here, because we are calling a mutable method on a value that must retain immutable?

Otherwise I think the issue can be closed for now.