Disable worker_threads by default for firebase compatibility

examples/with-firebase-authentication/next.config.js

@@ -0,0 +1,9 @@
+// Parallel builds are currently broken due to a limitation in grpc (a transitive firebase
+// dependency). Until this is fixed, a workaround is to set the number of available CPUs to 1.
+// https://github.com/zeit/next.js/issues/7894
+// https://github.com/grpc/grpc-node/issues/778
+module.exports = {
+  experimental: {
+    cpus: 1
+  }
+}

packages/next/build/index.ts

@@ -337,7 +337,7 @@ export default async function build(dir: string, conf = null): Promise<void> {
 
   const staticCheckWorkers = new Worker(staticCheckWorker, {
     numWorkers: config.experimental.cpus,
-    enableWorkerThreads: true,
+    enableWorkerThreads: config.experimental.workerThreads,
   })
 
   const analysisBegin = process.hrtime()
@@ -471,6 +471,7 @@ export default async function build(dir: string, conf = null): Promise<void> {
       sprPages,
       silent: true,
       buildExport: true,
+      threads: config.experimental.cpus,
       pages: combinedPages,
       outdir: path.join(distDir, 'export'),
     }

packages/next/build/webpack/plugins/terser-webpack-plugin/src/TaskRunner.js

@@ -28,8 +28,8 @@ export default class TaskRunner {
 
     if (this.maxConcurrentWorkers > 1) {
       this.workers = new Worker(worker, {
-        enableWorkerThreads: true,
         numWorkers: this.maxConcurrentWorkers,
+        enableWorkerThreads: true,
       })
       this.boundWorkers = options => this.workers.default(options)
     } else {

packages/next/export/index.ts

@@ -267,7 +267,7 @@ export default async function(
     {
       maxRetries: 0,
       numWorkers: threads,
-      enableWorkerThreads: true,
+      enableWorkerThreads: nextConfig.experimental.workerThreads,
       exposedMethods: ['default'],
     }
   ) as any

packages/next/next-server/server/config.ts

@@ -48,6 +48,7 @@ const defaultConfig: { [key: string]: any } = {
     publicDirectory: false,
     sprFlushToDisk: true,
     deferScripts: false,
+    workerThreads: true,
   },
   future: {
     excludeDefaultMomentLocales: false,

test/integration/firebase-grpc/pages/page-1.js

@@ -0,0 +1,2 @@
+import 'firebase/firestore'
+export default () => <div>Firebase</div>

test/integration/firebase-grpc/pages/page-2.js

@@ -0,0 +1,2 @@
+import 'firebase/firestore'
+export default () => <div>Firebase</div>

test/integration/firebase-grpc/test/index.test.js

@@ -0,0 +1,33 @@
+/* eslint-env jest */
+/* global jasmine */
+import path from 'path'
+import fs from 'fs-extra'
+import { nextBuild } from 'next-test-utils'
+
+jasmine.DEFAULT_TIMEOUT_INTERVAL = 1000 * 60 * 1
+const appDir = path.join(__dirname, '..')
+const nextConfig = path.join(appDir, 'next.config.js')
+
+describe('Builds with firebase dependency only sequentially', () => {
+  it('Throws an error when building with firebase dependency with worker_threads', async () => {
+    await fs.remove(nextConfig)
+    const results = await nextBuild(appDir, [], { stdout: true, stderr: true })
+    expect(results.stdout + results.stderr).toMatch(/Build error occurred/)
+    expect(results.stdout + results.stderr).toMatch(
+      /grpc_node\.node\. Module did not self-register\./
+    )
+  })
+
+  it('Throws no error when building with firebase dependency without worker_threads', async () => {
+    await fs.writeFile(
+      nextConfig,
+      `module.exports = { experimental: { workerThreads: false } }`
+    )
+    const results = await nextBuild(appDir, [], { stdout: true, stderr: true })
+    await fs.remove(nextConfig)
+    expect(results.stdout + results.stderr).not.toMatch(/Build error occurred/)
+    expect(results.stdout + results.stderr).not.toMatch(
+      /grpc_node\.node\. Module did not self-register\./
+    )
+  })
+})