.NET Core 3.0 + Angular 9 cli application called via the SpaServices extensions hangs in common configuration #17277

 Describe the bug

Running a .NET Core 3.0 + Angular 9 cli (version 9.0.0-rc.2 as of this post) with the angular cli build option progress set to false will hang until the StartupTimeout expires (default: 120 seconds)

To Reproduce

I created a repo with a bare bones .NET Core 3.0 + Angular 9 cli application to demo the bug. Simply clone, npm build the ClientApp folder, and dotnet run. Or you can follow the steps below to do this from scratch:

1. Ensure you have .NET Core 3.0 installed
2. Create a .NET Core application with the current Angular templates by typing: dotnet new angular -n HelloWorld
3. Navigate to the ClientApp folder and install the Typescript helper functions required for Angular 9 by typing: npm install tslib@latest
4. Update to Angular 9 by typing: ng update @angular/core @angular/cli --next
5. Ensure the progress build option in the angular.json file is set to false
6. Run the application by navigating back to the root folder and typing: dotnet run
7. Launch a browser and navigate to: https://localhost:5001

The application will hang and eventually timeout.

Further technical details

This appears to be caused by a change in how ng serve outputs to the console in the new Angular 9 CLI. The AngularCliMiddleware makes a WaitForMatch() method call against the standard output to signify when the Angular assets have been generated and the web server is ready to receive requests (Line 84). However, unless the progress option is set to true in the angular.json file you never see the expected line.

UPDATE: Updated to .NET Core 3.1 and Angular 9.0.0-rc.5. Same issue. New, simpler workaround is to modify your npm start script to perform a simple echo prior to ng serve (see comment below)

UPDATE (6/5/2020): Lots of recent comments so I figured I'd share exactly what has worked for me with every release of .NET and Angular since my original post. Update your package.json like so:

  "scripts": {
    "ng": "ng",
    "start": "echo hello && ng serve",
    "build": "ng build",
    "test": "ng test",
    "lint": "ng lint",
    "e2e": "ng e2e"
  }