fix(@angular-devkit/build-angular): ensure Sass worker implementation…

… supports Node.js 12.14

The Worker constructor option for a transfer list is unfortunately not supported until Node.js 12.17. For Node.js versions prior to 12.17, a manual message post is now used to transfer the necessary initialization data to the Sass workers.

packages/angular_devkit/build_angular/src/sass/sass-service.ts

@@ -39,6 +39,15 @@ interface RenderResponseMessage {
   result?: Result;
 }
 
+/**
+ * Workaround required for lack of new Worker transfer list support in Node.js prior to 12.17
+ */
+let transferListWorkaround = false;
+const version = process.versions.node.split('.').map((part) => Number(part));
+if (version[0] === 12 && version[1] < 17) {
+  transferListWorkaround = true;
+}
+
 /**
  * A Sass renderer implementation that provides an interface that can be used by Webpack's
  * `sass-loader`. The implementation uses a Worker thread to perform the Sass rendering
@@ -126,10 +135,14 @@ export class SassWorkerImplementation {
 
     const workerPath = require.resolve('./worker');
     const worker = new Worker(workerPath, {
-      workerData: { workerImporterPort, importerSignal },
-      transferList: [workerImporterPort],
+      workerData: transferListWorkaround ? undefined : { workerImporterPort, importerSignal },
+      transferList: transferListWorkaround ? undefined : [workerImporterPort],
     });
 
+    if (transferListWorkaround) {
+      worker.postMessage({ init: true, workerImporterPort, importerSignal }, [workerImporterPort]);
+    }
+
     worker.on('message', (response: RenderResponseMessage) => {
       const request = this.requests.get(response.id);
       if (!request) {

packages/angular_devkit/build_angular/src/sass/worker.ts

@@ -18,27 +18,46 @@ interface RenderRequestMessage {
    * importer on the main thread.
    */
   id: number;
+
   /**
    * The Sass options to provide to the `dart-sass` render function.
    */
   options: Options;
+
   /**
    * Indicates the request has a custom importer function on the main thread.
    */
   hasImporter: boolean;
+
+  /**
+   * Indicates this is not an init message.
+   */
+  init: undefined;
+}
+
+interface InitMessage {
+  init: true;
+  workerImporterPort: MessagePort;
+  importerSignal: Int32Array;
 }
 
-if (!parentPort || !workerData) {
+if (!parentPort) {
   throw new Error('Sass worker must be executed as a Worker.');
 }
 
 // The importer variables are used to proxy import requests to the main thread
-const { workerImporterPort, importerSignal } = workerData as {
-  workerImporterPort: MessagePort;
-  importerSignal: Int32Array;
-};
+let { workerImporterPort, importerSignal } = (workerData || {}) as InitMessage;
+
+parentPort.on('message', (message: RenderRequestMessage | InitMessage) => {
+  // The init message is only needed to support Node.js < 12.17 and can be removed once support is dropped
+  if (message.init) {
+    workerImporterPort = message.workerImporterPort;
+    importerSignal = message.importerSignal;
+
+    return;
+  }
 
-parentPort.on('message', ({ id, hasImporter, options }: RenderRequestMessage) => {
+  const { id, hasImporter, options } = message;
   try {
     if (hasImporter) {
       // When a custom importer function is present, the importer request must be proxied