ng add fails to find app.module.ts when using custom tsconfig.json paths

Start with packages/schematics/angular/utility/ng-ast-utils.ts, then compare how material2's setup-project.ts consumes the calculated app.module.ts path. Reproduce the failure with the linked repository by running ng add @angular/material after configuring tsconfig.json paths. Done means the command locates the module successfully when main.ts imports it through @app/app.module.

Bug Report or Feature Request (mark with an x)

- [X ] bug report -> please search issues before submitting
- [X ] feature request

Whether this is a bug or a feature depends on whether or not custom paths in tsconfig.json are supported with the Cli.

Command (mark with an x)

- [X ] add

Versions

Angular CLI: 7.0.2
Node: 10.8.0
OS: win32 x64
Angular: 7.0.0
... animations, common, compiler, compiler-cli, core, forms
... http, language-service, platform-browser
... platform-browser-dynamic, router

Repro steps

• ng new app-name (pick defaults)
• Add "paths": { "@app/*": ["src/app/*"] } to tsconfig.json
• Update main.ts to use this new path
  import { AppModule } from '@app/app.module';
import { environment } from './environments/environment';
• ng add @angular/material
• Select Yes for ? Set up browser animations for Angular Material?

Repository all set up to reproduce this error is available here.
Just clone and type ng add @angular/material.

The log given by the failure

Could not read Angular module file: /src/@app/app.module.ts

Desired functionality

Cli handles custom paths in tsconfig.json.

Mention any other details that might be useful

Here is where material tries to get the app.module.ts path
https://github.com/angular/material2/blob/985774a4eaa14d1dcbf1ad96ab176043d38f433e/src/lib/schematics/ng-add/setup-project.ts#L56

Here is where the path to app.module.ts is being calculated in the schematics code
https://github.com/angular/angular-cli/blob/82f2bda2f59e4665611d1a75b51a62bae21ac340/packages/schematics/angular/utility/ng-ast-utils.ts#L78

I believe the above link is what is causing the problem.

I've always preferred absolute urls in Angular apps compared to the relative paths (which become very difficult to read for nested components).

Adding custom paths to tsconfig.json works pretty well to solve this problem. VSCode works fine with it and the Cli has no other issues I've run into.

If using paths isn't officially supported does the Angular team recommend using relative paths like import { MyApiService } from '../../../../../my-api.service'?