Bundling the Loom extension

Vite bundles the extension for the VS Code extension host. It has two entry points — the client in this package and the language server in @athrio/loom-lang — and emits them as dist/client.js and dist/server.js. The extension host loads CommonJS, so the build emits CommonJS rather than the ESM the CLI produces.

The build

Some of the server's dependencies — the vscode-*-languageservice packages and jsonc-parser — ship only UMD bundles, the older module format that rolldown cannot follow statically. The umd2esm plugin rewrites each such import to its ESM sibling so the bundler can inline it. This is the same trick volarjs/starter uses.

vscode-markdown-languageservice, which ProseLanguage's Markdown service pulls in, imports vscode-uri by its default binding, which that package's ES-module build does not provide. An alias resolves vscode-uri to its UMD build instead, where the bundler's CommonJS interop supplies one.

TypeScript

import { defineConfig } from 'vite'
import { builtinModules, createRequire } from 'node:module'
import { dirname, resolve } from 'node:path'
import { fileURLToPath } from 'node:url'

const here = dirname(fileURLToPath(import.meta.url))
const requireFromHere = createRequire(import.meta.url)

const nodeBuiltins = [...builtinModules, ...builtinModules.map((m) => `node:${m}`)]

const umd2esm = {
  name: 'umd2esm',
  enforce: 'pre' as const,
  resolveId(source: string, importer: string | undefined) {
    if (/^(vscode-.*-languageservice|jsonc-parser)/.test(source)) {
      const fromDir = importer ? dirname(importer) : here
      const resolved = requireFromHere.resolve(source, { paths: [fromDir] })
      return resolved.replace(/\/umd\//, '/esm/').replace(/\\umd\\/g, '\\esm\\')
    }
    return null
  },
}

The vscode module is provided by the host at runtime, and Node's built-in modules are present in every Node runtime, so both stay external — everything else is inlined. The two entries build to dist/client.js and dist/server.js, targeting Node 20 in CommonJS form.

TypeScript

export default defineConfig({
  plugins: [umd2esm],
  resolve: {
    conditions: ['node'],
    mainFields: ['main', 'module'],
    alias: {
      'vscode-uri': requireFromHere
        .resolve('vscode-uri')
        .replace(/esm[\\/]index\.mjs$/, 'umd/index.js'),
    },
  },
  build: {
    target: 'node20',
    outDir: 'dist',
    emptyOutDir: true,
    sourcemap: true,
    minify: false,
    lib: {
      entry: {
        client: resolve(here, 'src/vscode-extension.ts'),
        server: resolve(here, '../loom-lang/src/index.ts'),
      },
      formats: ['cjs'],
    },
    rollupOptions: {
      external: ['vscode', ...nodeBuiltins],
      output: { entryFileNames: '[name].js' },
    },
  },
})

Loom