[Bug] Full runes mode support

[BlackySoul]

Describe the bug

If i set

compilerOptions: {
   runes: true,
}

in my svelte.config.js file, Storybook will fail to compile.

Steps to reproduce the behavior

1. Use default init project (npx sv create with storybook support)
2. Add

compilerOptions: {
   runes: true,
}

3. Run storybook
4. Error:

✘ [ERROR] node_modules/@storybook/addon-svelte-csf/dist/runtime/LegacyTemplate.svelte:14:2 Cannot use export let in runes mode — use $props() instead
https://svelte.dev/e/legacy_export_invalid [plugin vite-plugin-svelte:optimize]

Expected behavior

Storybook builds successfully

Screenshots and/or logs

Environment

• OS: iOS
• Node.js version: 24.11.0
• NPM version: 11.6.1
• Browser (if applicable): -
• Browser version (if applicable): -
• Device (if applicable): -

Additional context

Add any other context about the problem here.

[YungSeepferd]

Still relevant, very annoying bug. Prevents me from establishing a proper Svelte 5 Component Library for my team.

[xeho91]

Is any of you able to provide a reproduction?
Without it, we don't know where to look to find the bug

[BlackySoul]

Is any of you able to provide a reproduction? Without it, we don't know where to look to find the bug

You can reproduce this by creating a new project using:

npx sv create

Then add the following to your svelte.config.js:

compilerOptions: { runes: true }

Here is a minimal reproduction repository:

https://github.com/BlackySoul/svelte-csf-runes

To run it:

npm run storybook

[BlackySoul]

Still relevant, very annoying bug. Prevents me from establishing a proper Svelte 5 Component Library for my team.

As a workaround, I’m currently using the following in my svelte.config.js:

compilerOptions: {
  runes: process.env.STORYBOOK_BUILD === 'true' ? undefined : true,
},

[xeho91]

What's your use case that you need runes explicitly enabled?

[xeho91]

Based on your reproduction link, you have Svelte v5 installed, you don't need to use this option?

I can only imagine that this option existence reason is for Svelte to enforce runes from external libraries which haven't migrated to v5 yet. I could be wrong, but if I am, help me understand

[melledijkstra]

Still relevant. I am getting the same issue. Using Vite + Svelte 5. Would be nice to flip the switch completely to runes mode.

Version details installed (pnpm-workspace.yaml):

  # UI related
  svelte: ^5.56.8
  svelte-check: ^4.7.4

  # Storybook
  storybook: ^10.5.6
  '@storybook/addon-svelte-csf': ^5.1.2
  '@storybook/svelte': ^10.5.6
  '@storybook/svelte-vite': ^10.5.6

  # Vite Plugins
  '@sveltejs/vite-plugin-svelte': ^7.2.0
  '@tailwindcss/vite': ^4.3.3