svelte/packages/svelte/rollup.config.js

import fs from 'node:fs';
import { createRequire } from 'node:module';
import resolve from '@rollup/plugin-node-resolve';
import commonjs from '@rollup/plugin-commonjs';
import json from '@rollup/plugin-json';

// runs the version generation as a side-effect of importing
import './scripts/generate-version.js';

const require = createRequire(import.meta.url);

const internal = await import('./src/runtime/internal/index.js');
fs.writeFileSync(
	'src/compiler/compile/internal_exports.js',
	`// This file is automatically generated\n` +
		`export default new Set(${JSON.stringify(Object.keys(internal))});`
);

/**
 * @type {import("rollup").RollupOptions[]}
 */
export default [
	// Generate UMD build of the compiler so that Eslint/Prettier (which need CJS) and REPL (which needs UMD because browser) can use it
	{
		input: 'src/compiler/index.js',
		plugins: [
			{
				resolveId(id) {
					// Must import from the `css-tree` browser bundled distribution due to `createRequire` usage if importing from css-tree directly
					if (id === 'css-tree') {
						return require.resolve('./node_modules/css-tree/dist/csstree.esm.js');
					}
				}
			},
			resolve(),
			commonjs({
				include: ['../../node_modules/**', 'node_modules/**']
			}),
			json()
		],
		output: {
			file: 'compiler.cjs',
			format: 'umd',
			name: 'svelte',
			sourcemap: false,
			indent: false
		},
		external: []
	}
];