Cannot assign to derived state

[didier]

Describe the bug

Just importing anything from Formsnap breaks the Vite dev server due to assigning to a constant.

I did a fresh npm install and it started appearing, but I was already on v2.0.0 before, so I'm not sure what changed now.

✘ [ERROR] node_modules/.pnpm/formsnap@2.0.0_svelte@5.19.10_sveltekit-superforms@2.23.1_@sveltejs+kit@2.17.1_@sveltej_987bc4fecae302b24a2f444f97bc821a/node_modules/formsnap/dist/formsnap.svelte.js:27:8 Cannot assign to derived state
https://svelte.dev/e/constant_assignment [plugin vite-plugin-svelte-module:optimize-svelte]

    node_modules/.pnpm/formsnap@2.0.0_svelte@5.19.10_sveltekit-superforms@2.23.1_@sveltejs+kit@2.17.1_@sveltej_987bc4fecae302b24a2f444f97bc821a/node_modules/formsnap/dist/formsnap.svelte.js:27:8:
      27 │        this.#name = props.name;
         ╵         ^

  The plugin "vite-plugin-svelte-module:optimize-svelte" was triggered by this import

    node_modules/.pnpm/formsnap@2.0.0_svelte@5.19.10_sveltekit-superforms@2.23.1_@sveltejs+kit@2.17.1_@sveltej_987bc4fecae302b24a2f444f97bc821a/node_modules/formsnap/dist/index.js:1:75:
      1 │ export { useFormField, useFormControl, getFormField, getFormControl } from "./formsnap.svelte.js";
        ╵                                                                            ~~~~~~~~~~~~~~~~~~~~~~

Reproduction

https://stackblitz.com/edit/sveltejs-kit-template-default-2bpq2kq9?file=src%2Froutes%2F%2Bpage.svelte

System Info

See Stackblitz repro.

Severity

blocking all usage of Formsnap

[zachstence]

If you pin svelte to 5.19.9 the problem is fixed. svelte@5.19.10 was just released 2 hours ago, seems to have caused this somehow.

https://stackblitz.com/edit/sveltejs-kit-template-default-bekldygt?file=package.json

[zachstence]

Looks like this was an expected change in Svelte with this PR
sveltejs/svelte#15228

[huntabyte]

I will investigate further but this seems like a bug with Svelte, as that line it is highlighting as assigning to derived state is not assigning to derived state.

[huntabyte]

This was a bug introduced by Svelte. There appears to be a fix PR submitted already so let's hope it gets merged/released soon :) sveltejs/svelte#15276

[dimfeld]

Svelte 5.20 was just released with the above-mentioned PR. I just upgraded my code to it and don't see the error anymore so I think we're good here!

[huntabyte]

Awesome, thanks for the update @dimfeld !