`await isn't allowed in non-async function` when assigning `{@const ... await}` inside `{#each...}` block

[Tinggaard]

Describe the bug

It is not possible to use asynchronous function calls ({@const foo = await fn()}) inside of an {#each} block.

It is possible to mitigate it by passing the data directly to a component instead.

Reproduction

{#each { length: 1 } as _}
  {@const data = await Promise.resolve("data")}
{/each}

https://stackblitz.com/github/tinggaard/await-in-non-async-fn

Edit: For some reason this does not throw in the Svelte REPL. see:
https://svelte.dev/playground/68548d8982b34b35a121594bda946ad5

Logs

[vite] (ssr) Error when evaluating SSR module /src/routes/+page.svelte: Parse failure: await isn't allowed in non-async function
At file: /src/routes/+page.svelte:16:18
  File: /src/routes/+page.svelte:16:18
  14 |  			for (let $$index = 0, $$length = each_array.length; $$index < $$length; $$index++) {
  15 |  				let _ = each_array[$$index];
  16 |  				const data = (await $.save(Promise.resolve("data")))();
     |                    ^
  17 |  			}
  18 |

System Info

System:
    OS: Linux 6.17 Arch Linux
    CPU: (16) x64 AMD Ryzen 7 8845HS w/ Radeon 780M Graphics
    Memory: 7.12 GB / 27.15 GB
    Container: Yes
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 24.9.0 - /usr/bin/node
    npm: 11.6.1 - /usr/bin/npm
    pnpm: 10.18.0 - /usr/bin/pnpm
  Browsers:
    Brave Browser: 139.1.81.137
    Chromium: 141.0.7390.54
    Firefox: 143.0.4
    Firefox Developer Edition: 143.0.4
  npmPackages:
    @sveltejs/adapter-auto: ^6.1.1 => 6.1.1 
    @sveltejs/kit: ^2.46.4 => 2.46.4 
    @sveltejs/vite-plugin-svelte: ^6.2.1 => 6.2.1 
    svelte: ^5.39.11 => 5.39.11 
    vite: ^7.1.9 => 7.1.9

Severity

blocking an upgrade

[paoloricciuti]

I suspect this is already fixed by #16919 can you verify with the pkg.pr.new package?

[paoloricciuti]

Uh actuallty probably no because that only touched the svelte boundary