svelte:boundary does not catch errors inside async component scripts

[santiagocezar]

Describe the bug

i'm using the experimental async feature, svelte:boundary does catch errors when using {await ...} in the markup, but it doesn't if the await is inside the component's script tag.

Reproduction

https://svelte.dev/playground/4bea921679af4be984e73bf9f38c804c?version=latest

Logs

Uncaught (in promise) failed to fetch data (in component script)

System Info

System:
    OS: Linux 6.15 Fedora Linux 42 (Toolbx Container Image)
    CPU: (16) x64 AMD Ryzen 7 7730U with Radeon Graphics
    Memory: 3.77 GB / 14.96 GB
    Container: Yes
    Shell: 5.2.37 - /usr/bin/bash
  Binaries:
    Node: 22.17.0 - /usr/bin/node
    pnpm: 10.9.0 - /usr/bin/pnpm
    bun: 1.2.19 - /usr/local/bin/bun
  npmPackages:
    svelte: ^5.37.1 => 5.37.1

Severity

annoyance

[jortuck]

I have also encountered this issue. I found a work around but it is a bit hacky.

If you wrap your await expression in a $derrived rune, and also put the contents of your components in it's own svelte boundary, you can catch the error in that local svelte boundary. However, this introduces another issue where it does not use the local pending() snippet, but the parent one instead. Here is a fork of your playground with an example:

https://svelte.dev/playground/ff0a91f38aea4efa856ca0a02d63c8fa?version=5.37.1

I am unsure yet if this is a bug or if I am using the async features incorrectly.

[santiagocezar]

yep that seems quite dirty ><

i'm guessing that the $derived helps because it's lazily evaluated during rendering? though i don't know why the local boundary makes a difference