feat: allow parallel worker builds when worker plugins is a function

docs/config/worker-options.md

@@ -11,10 +11,14 @@ Output format for worker bundle.
 
 ## worker.plugins
 
-- **Type:** [`(Plugin | Plugin[])[]`](./shared-options#plugins)
+- **Type:** [`(() => (Plugin | Plugin[])[]) | (Plugin | Plugin[])[]`](./shared-options#plugins)
 
 Vite plugins that apply to worker bundle. Note that [config.plugins](./shared-options#plugins) only applies to workers in dev, it should be configured here instead for build.
 
+Providing a function that returns an array of plugins is preferred, so we can safely run parallel builds for workers. The function should be side effect free and return the same array of plugins every time.
+
+When providing an array of plugins, the worker builds will run sequentially and workers nested inside other workers may not build.
+
 ## worker.rollupOptions
 
 - **Type:** [`RollupOptions`](https://rollupjs.org/configuration-options/)

packages/vite/src/node/__tests__/config.spec.ts

@@ -335,3 +335,36 @@ describe('resolveConfig', () => {
     expect(results2.clearScreen).toBe(false)
   })
 })
+
+describe('worker config', () => {
+  const userPlugin = (): PluginOption => {
+    return {
+      name: 'vite-plugin-worker-user-plugin',
+    }
+  }
+
+  test('resolves to default plugins function', async () => {
+    const results = await resolveConfig({}, 'build')
+    expect(typeof results.worker.plugins).toBe('function')
+  })
+
+  test('resolves to plugins function when user defined function given', async () => {
+    const config: InlineConfig = {
+      worker: {
+        plugins: () => [userPlugin()],
+      },
+    }
+    const results = await resolveConfig(config, 'build')
+    expect(typeof results.worker.plugins).toBe('function')
+  })
+
+  test('resolves to a plugins array when user defined array given', async () => {
+    const config: InlineConfig = {
+      worker: {
+        plugins: [userPlugin()],
+      },
+    }
+    const results = await resolveConfig(config, 'build')
+    expect(Array.isArray(results.worker.plugins)).toBe(true)
+  })
+})

packages/vite/src/node/config.ts

@@ -270,7 +270,7 @@ export interface UserConfig {
     /**
      * Vite plugins that apply to worker bundle
      */
-    plugins?: PluginOption[]
+    plugins?: PluginOption[] | (() => PluginOption[])
     /**
      * Rollup options to build worker bundle
      */
@@ -332,7 +332,7 @@ export interface LegacyOptions {
 
 export interface ResolveWorkerOptions extends PluginHookUtils {
   format: 'es' | 'iife'
-  plugins: Plugin[]
+  plugins: Plugin[] | (() => Promise<Plugin[]>)
   rollupOptions: RollupOptions
 }
 
@@ -454,12 +454,6 @@ export async function resolveConfig(
       return p.apply === command
     }
   }
-  // Some plugins that aren't intended to work in the bundling of workers (doing post-processing at build time for example).
-  // And Plugins may also have cached that could be corrupted by being used in these extra rollup calls.
-  // So we need to separate the worker plugin from the plugin that vite needs to run.
-  const rawWorkerUserPlugins = (
-    (await asyncFlatten(config.worker?.plugins || [])) as Plugin[]
-  ).filter(filterPlugin)
 
   // resolve plugins
   const rawUserPlugins = (
@@ -653,18 +647,39 @@ export async function resolveConfig(
 
   const BASE_URL = resolvedBase
 
+  // Some plugins that aren't intended to work in the bundling of workers (doing post-processing at build time for example).
+  // And Plugins may also have cached that could be corrupted by being used in these extra rollup calls.
+  // So we need to separate the worker plugin from the plugin that vite needs to run.
+  const rawWorkerUserPlugins = config.worker?.plugins
+  const supportsUserPluginsFunction =
+    typeof rawWorkerUserPlugins === 'function' || !rawWorkerUserPlugins
+  const getSortedWorkerUserPlugins = async (
+    userPlugins?: PluginOption[] | (() => PluginOption[]),
+  ) => {
+    const plugins =
+      typeof userPlugins === 'function' ? userPlugins() : userPlugins
+    const pluginsFlattened = (
+      (await asyncFlatten(plugins || [])) as Plugin[]
+    ).filter(filterPlugin)
+    return sortUserPlugins(pluginsFlattened)
+  }
+
   // resolve worker
   let workerConfig = mergeConfig({}, config)
   const [workerPrePlugins, workerNormalPlugins, workerPostPlugins] =
-    sortUserPlugins(rawWorkerUserPlugins)
+    await getSortedWorkerUserPlugins(rawWorkerUserPlugins)
 
   // run config hooks
-  const workerUserPlugins = [
+  const workerUserPluginsForHooks = [
     ...workerPrePlugins,
     ...workerNormalPlugins,
     ...workerPostPlugins,
   ]
-  workerConfig = await runConfigHook(workerConfig, workerUserPlugins, configEnv)
+  workerConfig = await runConfigHook(
+    workerConfig,
+    workerUserPluginsForHooks,
+    configEnv,
+  )
   const resolvedWorkerOptions: ResolveWorkerOptions = {
     format: workerConfig.worker?.format || 'iife',
     plugins: [],
@@ -754,15 +769,17 @@ export async function resolveConfig(
     isWorker: true,
     mainConfig: resolved,
   }
-  resolvedConfig.worker.plugins = await resolvePlugins(
-    workerResolved,
-    workerPrePlugins,
-    workerNormalPlugins,
-    workerPostPlugins,
-  )
+
+  const getResolvedWorkerPlugins = async () => {
+    return resolvePlugins(
+      workerResolved,
+      ...(await getSortedWorkerUserPlugins(rawWorkerUserPlugins)),
+    )
+  }
+
   Object.assign(
     resolvedConfig.worker,
-    createPluginHookUtils(resolvedConfig.worker.plugins),
+    createPluginHookUtils(await getResolvedWorkerPlugins()),
   )
 
   // call configResolved hooks
@@ -775,6 +792,10 @@ export async function resolveConfig(
       .map((hook) => hook(workerResolved)),
   ])
 
+  resolvedConfig.worker.plugins = supportsUserPluginsFunction
+    ? () => getResolvedWorkerPlugins()
+    : await getResolvedWorkerPlugins()
+
   // validate config
 
   if (middlewareMode === 'ssr') {
@@ -812,7 +833,10 @@ export async function resolveConfig(
     plugins: resolved.plugins.map((p) => p.name),
     worker: {
       ...resolved.worker,
-      plugins: resolved.worker.plugins.map((p) => p.name),
+      plugins: (typeof resolved.worker.plugins === 'function'
+        ? await resolved.worker.plugins()
+        : resolved.worker.plugins
+      ).map((p) => p.name),
     },
   })
 
@@ -856,7 +880,7 @@ assetFileNames isn't equal for every build.rollupOptions.output. A single patter
   ) {
     resolved.logger.warn(
       colors.yellow(`
-(!) Experimental legacy.buildSsrCjsExternalHeuristics and ssr.format: 'cjs' are going to be removed in Vite 5. 
+(!) Experimental legacy.buildSsrCjsExternalHeuristics and ssr.format: 'cjs' are going to be removed in Vite 5.
     Find more information and give feedback at https://github.com/vitejs/vite/discussions/13816.
 `),
     )

packages/vite/src/node/plugins/worker.ts

@@ -42,29 +42,36 @@ function saveEmitWorkerAsset(
 }
 
 // Ensure that only one rollup build is called at the same time to avoid
-// leaking state in plugins between worker builds.
-// TODO: Review if we can parallelize the bundling of workers.
+// leaking state in plugins between worker builds when running sequentially.
 const workerConfigSemaphore = new WeakMap<
   ResolvedConfig,
   Promise<OutputChunk>
 >()
-export async function bundleWorkerEntry(
+export async function handleBundleWorkerEntry(
   config: ResolvedConfig,
   id: string,
   query: Record<string, string> | null,
 ): Promise<OutputChunk> {
+  // When plugins are a function we can assume that plugins are instantiated separately
+  // and have a separate state. This means that we can run the worker builds in parallel.
+  const canRunParallel = typeof config.worker.plugins === 'function'
+
+  if (canRunParallel) {
+    return bundleWorkerEntry(config, id, query)
+  }
+
   const processing = workerConfigSemaphore.get(config)
   if (processing) {
     await processing
     return bundleWorkerEntry(config, id, query)
   }
-  const promise = serialBundleWorkerEntry(config, id, query)
+  const promise = bundleWorkerEntry(config, id, query)
   workerConfigSemaphore.set(config, promise)
   promise.then(() => workerConfigSemaphore.delete(config))
   return promise
 }
 
-async function serialBundleWorkerEntry(
+async function bundleWorkerEntry(
   config: ResolvedConfig,
   id: string,
   query: Record<string, string> | null,
@@ -75,7 +82,7 @@ async function serialBundleWorkerEntry(
   const bundle = await rollup({
     ...rollupOptions,
     input: cleanUrl(id),
-    plugins,
+    plugins: typeof plugins === 'function' ? await plugins() : plugins,
     onwarn(warning, warn) {
       onRollupWarning(warning, warn, config)
     },
@@ -173,7 +180,7 @@ export async function workerFileToUrl(
   const workerMap = workerCache.get(config.mainConfig || config)!
   let fileName = workerMap.bundle.get(id)
   if (!fileName) {
-    const outputChunk = await bundleWorkerEntry(config, id, query)
+    const outputChunk = await handleBundleWorkerEntry(config, id, query)
     fileName = outputChunk.fileName
     saveEmitWorkerAsset(config, {
       fileName,

playground/worker/__tests__/es/es-worker.spec.ts

@@ -61,7 +61,7 @@ describe.runIf(isBuild)('build', () => {
   test('inlined code generation', async () => {
     const assetsDir = path.resolve(testDir, 'dist/es/assets')
     const files = fs.readdirSync(assetsDir)
-    expect(files.length).toBe(28)
+    expect(files.length).toBe(29)
     const index = files.find((f) => f.includes('main-module'))
     const content = fs.readFileSync(path.resolve(assetsDir, index), 'utf-8')
     const worker = files.find((f) => f.includes('my-worker'))

playground/worker/__tests__/parallel/parallel-worker-build.spec.ts

@@ -0,0 +1,17 @@
+import { describe, test } from 'vitest'
+import { isBuild, page, untilUpdated } from '~utils'
+
+describe.runIf(isBuild)('build', () => {
+  test('expect the plugin state to be unpolluted and match across worker builds', async () => {
+    await untilUpdated(
+      () => page.textContent('.nested-worker-plugin-state'),
+      '"data":1',
+      true,
+    )
+    await untilUpdated(
+      () => page.textContent('.sub-worker-plugin-state'),
+      '"data":1',
+      true,
+    )
+  })
+})

playground/worker/__tests__/serial/serial-worker-build.spec.ts

@@ -0,0 +1,18 @@
+import { describe, test } from 'vitest'
+import { isBuild, page, untilUpdated } from '~utils'
+
+describe.runIf(isBuild)('build', () => {
+  test('expect the plugin state to be polluted and not match across worker builds', async () => {
+    await untilUpdated(
+      () => page.textContent('.nested-worker-plugin-state'),
+      '"data":1',
+      true,
+    )
+    // The plugin state is polluted and should have a different data value from the sub worker
+    await untilUpdated(
+      () => page.textContent('.sub-worker-plugin-state'),
+      '"data":2',
+      true,
+    )
+  })
+})

playground/worker/index.html

@@ -89,6 +89,18 @@ <h2 class="format-iife">format iife:</h2>
 </p>
 <code class="nested-worker-constructor"></code>
 
+<p>
+  import NestedWorker from './worker-nested-worker?worker' - plugin-state
+  <span class="classname">.nested-worker-plugin-state</span>
+</p>
+<code class="nested-worker-plugin-state"></code>
+
+<p>
+  import SubWorker from './sub-worker?worker' - plugin-state
+  <span class="classname">.sub-worker-plugin-state</span>
+</p>
+<code class="sub-worker-plugin-state"></code>
+
 <p>
   new Worker(new URL('./classic-worker.js', import.meta.url))
   <span class="classname">.classic-worker</span>

playground/worker/modules/test-state.js

@@ -0,0 +1 @@
+export const state = 0

playground/worker/sub-worker.js

@@ -1,6 +1,10 @@
+import { state } from './modules/test-state.js'
+
+self.postMessage({ type: 'plugin-state-sub', data: state })
+
 self.onmessage = (event) => {
   if (event.data === 'ping') {
-    self.postMessage(`pong ${self.location.href}`)
+    self.postMessage({ type: 'module', data: `pong ${self.location.href}` })
   }
 }
 

playground/worker/vite.config-parallel.js

@@ -0,0 +1,35 @@
+import { defineConfig } from 'vite'
+import workerPluginTestPlugin from './worker-plugin-test-plugin'
+import workerPluginStatePlugin from './worker-plugin-state-plugin'
+
+export default defineConfig({
+  base: '/serial/',
+  resolve: {
+    alias: {
+      '@': __dirname,
+    },
+  },
+  worker: {
+    format: 'iife',
+    plugins: () => [workerPluginTestPlugin(), workerPluginStatePlugin()],
+    rollupOptions: {
+      output: {
+        assetFileNames: 'assets/worker_asset-[name].[ext]',
+        chunkFileNames: 'assets/worker_chunk-[name].js',
+        entryFileNames: 'assets/worker_entry-[name].js',
+      },
+    },
+  },
+  build: {
+    outDir: 'dist/parallel',
+    rollupOptions: {
+      output: {
+        assetFileNames: 'assets/[name].[ext]',
+        chunkFileNames: 'assets/[name].js',
+        entryFileNames: 'assets/[name].js',
+      },
+    },
+  },
+  plugins: [workerPluginTestPlugin()],
+  cacheDir: 'node_modules/.vite-es',
+})

playground/worker/vite.config-serial.js

@@ -0,0 +1,35 @@
+import { defineConfig } from 'vite'
+import workerPluginTestPlugin from './worker-plugin-test-plugin'
+import workerPluginStatePlugin from './worker-plugin-state-plugin'
+
+export default defineConfig({
+  base: '/serial/',
+  resolve: {
+    alias: {
+      '@': __dirname,
+    },
+  },
+  worker: {
+    format: 'iife',
+    plugins: [workerPluginTestPlugin(), workerPluginStatePlugin()],
+    rollupOptions: {
+      output: {
+        assetFileNames: 'assets/worker_asset-[name].[ext]',
+        chunkFileNames: 'assets/worker_chunk-[name].js',
+        entryFileNames: 'assets/worker_entry-[name].js',
+      },
+    },
+  },
+  build: {
+    outDir: 'dist/serial',
+    rollupOptions: {
+      output: {
+        assetFileNames: 'assets/[name].[ext]',
+        chunkFileNames: 'assets/[name].js',
+        entryFileNames: 'assets/[name].js',
+      },
+    },
+  },
+  plugins: [workerPluginTestPlugin()],
+  cacheDir: 'node_modules/.vite-es',
+})