error NG6002: Appears in the NgModule.imports of AppModule, but could not be resolved to an NgModule class

🔑 Title: How to Fix the "error NG6002" in Angular 9 with Ivy and Angular Fire 6 🚀

👋 Hey there, fellow Angular developer! Are you getting the "error NG6002: Appears in the NgModule.imports of AppModule, but could not be resolved to an NgModule class" error? Don't worry, we've got you covered! 😎

🤔 The Problem: This error usually occurs when you have a module imported in your AppModule, but Angular is unable to find the corresponding NgModule class. It often happens when there is a mismatch in the versions or configurations of your Angular modules.

🌱 The Cause: Based on your context, the issue might be related to Ivy, Angular's new rendering engine. However, this error can have multiple causes, so let's dive into potentially common issues and their solutions! 💪

🔧 Common Solutions: Here are a few steps you can take to resolve this issue:

1. Check Compatibility: Ensure that the versions of your Angular packages are compatible with each other. In your package.json, some dependencies like @angular/fire and @angular/material have specific versions mentioned. Make sure they are compatible with Angular 9.

2. Clean Rebuild: Sometimes, the issue is caused by artifacts from previous builds. Try cleaning your project's build artifacts using the following commands:

   ng clean ng build

3. Update Ivy Configuration: By default, Angular projects use Ivy as the rendering engine. However, if you are facing issues with it, you can opt out and switch back to the older View Engine. In your tsconfig.app.json, add the following compilerOptions:

   "angularCompilerOptions": { "enableIvy": false }

   Then, recompile your project using ng build.

4. Verify Imports: Double-check if the module you are importing in your AppModule is exported correctly as an NgModule class. Check the spelling, casing, and location of the imported module.

5. Check tsconfig.app.json: In some cases, the issue may lie in the tsconfig.app.json file. Make sure that the file paths mentioned in the "files" and "include" sections are correct and point to the necessary TypeScript files.

6. Verify Module Dependencies: If the error persists, verify that the imported module and all its dependencies are correctly installed. Run npm install to ensure that all modules are up to date.

🎯 Next Steps: If the above solutions don't resolve the issue, double-check your environment setup and the way you've installed Angular Fire 6. It's always a good idea to refer to the official documentation or seek help from the Angular community.

So go ahead and give these solutions a try! We hope one of them solves your problem. 🙌

🎉 Call-to-Action: Have you encountered the "error NG6002" before? How did you solve it? Share your experiences and let us know in the comments below! We'd love to hear your insights and help you out. Happy coding! 💻😊