storybook/code/frameworks/svelte-vite/src/preset.ts

import { type StorybookConfig, hasVitePlugins } from '@storybook/builder-vite';
import { handleSvelteKit } from './utils';
import { svelteDocgen } from './plugins/svelte-docgen';

export const core: StorybookConfig['core'] = {
  builder: '@storybook/builder-vite',
  renderer: '@storybook/svelte',
};

export const viteFinal: NonNullable<StorybookConfig['viteFinal']> = async (config, options) => {
  const { plugins = [] } = config;
  // TODO: set up eslint import to use typescript resolver
  // eslint-disable-next-line import/no-unresolved
  const { svelte, loadSvelteConfig } = await import('@sveltejs/vite-plugin-svelte');
  const svelteOptions: Record<string, any> = await options.presets.apply(
    'svelteOptions',
    {},
    options
  );
  const svelteConfig = { ...(await loadSvelteConfig()), ...svelteOptions };

  // Add svelte plugin if not present
  if (!(await hasVitePlugins(plugins, ['vite-plugin-svelte']))) {
    plugins.push(svelte());
  }

  // Add docgen plugin
  plugins.push(svelteDocgen(svelteConfig));

  await handleSvelteKit(plugins, options);

  return {
    ...config,
    plugins,
  };
};