title: Cannot find module when using custom import paths with multiple tsconfigs
body: <p>I've got a project with multiple <code>tsconfig.json</code> files. I'd like to shorten all imports, but for some reason shortened imports doesn't work in a specific scenario.</p>
  
  <p>The project structure:</p>
  
  <pre><code>foo/
  |  main.ts
  |  tsconfig.json
  projects/
  |  bar/
  |    index.ts
  tsconfig.json
  </code></pre>
  
  <p>Whenever I want to compile <code>foo/main.ts</code> I get the following error: <code>Cannot find module @bar/shared</code>.</p>
  
  <p>Some details:</p>
  
  <p>The <code>projects/bar/index.ts</code> file simply exports a plain class: <code>export class Foo {}</code></p>
  
  <p>The <code>foo/main.ts</code> tries to import the <code>Foo</code> class:</p>
  
  <pre><code>import {Foo} from '@bar/shared';
  </code></pre>
  
  <p>Last but not least the <code>tsconfig.json</code> within <code>foo</code>:</p>
  
  <pre><code>{
    "extends": "../tsconfig.json",
    "compilerOptions": {
      "target": "es2015",
      "module": "commonjs",
      "moduleResolution": "node",
      "experimentalDecorators": true,
      "emitDecoratorMetadata": true,
      "resolveJsonModule": true,
      "lib": ["es6", "dom"],
      "types": [
        "node"
      ],
      "outDir": "../dist/foo"
    }
  }
  </code></pre>
  
  <p>And the root <code>tsconfig.json</code>:</p>
  
  <pre><code>{
    "compileOnSave": false,
    "compilerOptions": {
      "baseUrl": "./",
      "outDir": "./dist/out-tsc",
      "sourceMap": true,
      "declaration": false,
      "module": "es2015",
      "moduleResolution": "node",
      "emitDecoratorMetadata": true,
      "experimentalDecorators": true,
      "importHelpers": true,
      "target": "es5",
      "typeRoots": [
        "node_modules/@types"
      ],
      "lib": [
        "es2018",
        "dom"
      ],
      "paths": {
        "@bar/shared": ["projects/bar"]
      }
    }
  }
  </code></pre>
  
  <p>My IDE is completely satisfied - but I'm unable to compile.</p>