Svelte 5: onanimationend event doesn't get called under these specific circumstances.

[HighFunctioningSociopathSH]

Describe the bug

After updating to [email protected], I noticed that the animations of my component don't work properly anymore and found out that my onanimationend event is not getting triggered. After a considerable amount of searching I found out that under the following conditions, the onanimationend event doesn't trigger.

Reproduction

Test.svelte

<script lang="ts">
  import "./styles.scss";
  let { ...restProps } = $props();
</script>

<span
  {...restProps}
  class="test"
  ontransitionend={(e) => {
    // content doesn't matter
  }}
  onanimationend={(e) => {
    console.log("called");
  }}
>
</span>

styles.css

.test {
  width: 10rem;
  height: 10rem;
  background-color: red;
  display: inline-block;
  @keyframes test-animation {
    from {
      opacity: 0;
    }
    to {
      opacity: 1;
    }
  }
  animation: test-animation 2s linear forwards;
}

+page.svelte

<script lang="ts">
  import Test from "$components/Test/Test.svelte";
</script>

<Test></Test>

Try removing the restProps spread and you will see that the onanimationend event gets called. you can do the same thing for ontransitionend and witness that again the onanimationend event gets called. Only when both the {...restProps} and ontransitionend props are present, the onanimationend event is ignored. I'm not sure if this only happens for these events or if other things can also cause the same issue. All I can say for sure is that this issue wasn't present in [email protected]

Logs

No response

System Info

System:
    OS: Windows 11 10.0.22631
    CPU: (16) x64 12th Gen Intel(R) Core(TM) i7-12650H
    Memory: 5.18 GB / 15.63 GB
  Binaries:
    Node: 20.12.2 - C:\Program Files\nodejs\node.EXE
    npm: 10.5.0 - C:\Program Files\nodejs\npm.CMD
    bun: 1.1.3 - ~\.bun\bin\bun.EXE
  Browsers:
    Edge: Chromium (123.0.2420.97)
    Internet Explorer: 11.0.22621.3527
  npmPackages:
    svelte: ^5.0.0-next.141 => 5.0.0-next.141

Severity

blocking an upgrade

[FoHoOV]

here is simpler demo. It seems its not about the props, just any spearding causes this issue.