node-sass sometimes hangs because of how it works natively

change/just-scripts-2020-10-01-10-54-45-node-sass.json

@@ -0,0 +1,8 @@
+{
+  "type": "patch",
+  "comment": "adds some safe-guard against stalling with node-sass in sassTask",
+  "packageName": "just-scripts",
+  "email": "kchau@microsoft.com",
+  "dependentChangeType": "patch",
+  "date": "2020-10-01T17:54:45.328Z"
+}

packages/just-scripts/src/tasks/sassTask.ts

@@ -10,13 +10,18 @@ export interface SassTaskOptions {
   postcssPlugins?: any[];
 }
 
+let processHandlerSet = false;
+
 export function sassTask(options: SassTaskOptions): TaskFunction;
 /** @deprecated Use object param version */
 export function sassTask(createSourceModule: (fileName: string, css: string) => string, postcssPlugins?: any[]): TaskFunction;
 export function sassTask(
   optionsOrCreateSourceModule: SassTaskOptions | ((fileName: string, css: string) => string),
   postcssPlugins?: any[]
 ): TaskFunction {
+  // node-sass causes strange behavior when it fails. It sometimes hangs the whole process
+  setUncaughtExceptionHandler();
+
   let createSourceModule: (fileName: string, css: string) => string;
   if (typeof optionsOrCreateSourceModule === 'function') {
     createSourceModule = optionsOrCreateSourceModule;
@@ -35,7 +40,7 @@ export function sassTask(
 
     if (!nodeSass || !postcss || !autoprefixer) {
       logger.warn('One of these [node-sass, postcss, autoprefixer] is not installed, so this task has no effect');
-      done();
+      cleanUpAndDone(done);
       return;
     }
 
@@ -84,9 +89,9 @@ export function sassTask(
           }
       );
 
-      parallelLimit(tasks, 5, done);
+      parallelLimit(tasks, 5, err => cleanUpAndDone(done, err));
     } else {
-      done();
+      cleanUpAndDone(done);
     }
   };
 }
@@ -107,3 +112,43 @@ function patchSassUrl(url: string, _prev: string, _done: any) {
 
   return { file: newUrl };
 }
+
+/**
+ * sets up an uncaughtException handler for node-sass
+ */
+function setUncaughtExceptionHandler() {
+  if (!processHandlerSet) {
+    processHandlerSet = true;
+    process.on('uncaughtException', uncaughtExceptionHandler);
+  }
+}
+
+/**
+ * unsets the uncaughtException handler for node-sass
+ */
+function unsetUncaughtExceptionHandler() {
+  if (processHandlerSet) {
+    processHandlerSet = false;
+    process.off('uncaughtException', uncaughtExceptionHandler);
+  }
+}
+
+/**
+ * The uncaughtExceptionHandler is a work around for node-sass hanging
+ * See: https://github.com/sass/node-sass/issues/1048
+ * @param e
+ */
+function uncaughtExceptionHandler(e: Error) {
+  console.error(e.stack);
+  process.kill(process.pid, 'SIGINT');
+}
+
+/**
+ * In order for us to clean up the exception handler, we attach the clean up to the "done" callback
+ * @param done
+ * @param e
+ */
+function cleanUpAndDone(done: (e?: Error) => void, e?: Error) {
+  unsetUncaughtExceptionHandler();
+  return done(e);
+}