next.168 development mode and component snippets inside loop

[vits]

Describe the bug

While next.168 fixed #12233, it introduced new problem in development mode.
Component's default snippet (haven't tried named snippets) keeps previous output and appends new one if component is inside loop and array is changed, and {#each} tag has key value. It works as expected without key value and in production mode.

Reproduction

Simple component with default children snippet.

<script>
  const { children } = $props();
</script>
{@render children()}

App code

<script>
import Component from "./Component.svelte";
const sample1 = [{name: "A"}, {name: "B"}];
const sample2 = [{name: "C"}, {name: "D"}];
let items = $state(sample1);

const replace = () => {
  items = $state.is(items, sample1) ? sample2 : sample1;
}
</script>

<button onclick={replace}>replace</button>

{#each items as item (item.name)}
  <Component>
    {item.name}
  </Component>
{/each}

Logs

No response

System Info

next.168

Severity

blocking all usage of svelte

[trueadm]

REPL

Looks to be a regression from #12215. Looking into it when we go to remove the each block entries, the anchor and end nodes are the same, even though they have content from the snippet.

Oddly the bug doesn't happen in the REPL, but does locally. So maybe it's related to the HMR bug. #12243

[vits]

Don't know whether this is related and helps, but some problem with loops and snippets was introduced in next.162. It was different - everything worked fine in development (HMR) but was broken in production. Don't have full example, but something like this

{#each data as row (row.id)}
  <Row>
    {#each columns as column (column.name)}
      <Cell>
        {column.name}
      </Cell>
    {/each}
  </Row>
{/each}

In production this ended with empty rows after changing data array, while everything was as expected locally. This was fixed in next.167 (works as expected both locally and in production) but introduced #12233. And now in next.168 it's still fixed in production but preserves all old rows (outer loop) in HMR. Didn't try changing inner loop array (columns) though.

[Dudek-AMS]

isnt loop or if related

#12247

[dummdidumm]

For everyone experiencing this: you can disable hot module reloading through the compilerOptions.hmr setting until this is fixed.

[dummdidumm]

closing as duplicate of #12243