title: Extending tsconfig.json file doesn't seem to extend anything
body: <p>I have a project from which I need to build two different products. Say I have</p>
  
  <pre><code>./src/advanced
  ./src/basic
  </code></pre>
  
  <p>All code is written in Typescript so I need to compile this with <code>tsc</code></p>
  
  <p>Because of this, I created 3 <strong>tsconfig</strong> files</p>
  
  <p><em>tsconfig-base.json</em></p>
  
  <pre><code>{
    "compilerOptions": {
      "module": "commonjs",
      "declaration": true,
      "noImplicitAny": false,
      "removeComments": true,
      "emitDecoratorMetadata": true,
      "experimentalDecorators": true,
      "target": "es6",
      "sourceMap": true,
      "outDir": "./dist",
      "baseUrl": "./src",
      "lib": ["es2018", "dom", "dom", "dom.iterable", "es6"],
      "importHelpers": true,
    },
    "exclude": ["node_modules", "**/*.spec.ts","dist"]
  </code></pre>
  
  <p>Now to build the <code>basic</code> product I have</p>
  
  <p><em>tsconfig-basic.json</em></p>
  
  <pre><code>{
    "extends": "./tsconfig-base.json",
    "compilerOptions": {
      "noEmitHelpers": true
    },
    "files": [
       "basic/main.ts"
    ]
  }
  </code></pre>
  
  <p>And I compile as follows</p>
  
  <pre><code>$&gt; tsc -p ./tsconfig-basic.json
  </code></pre>
  
  <p>Now I have 2 issues</p>
  
  <p>1) The file <code>basic/main.ts</code> cannot be found, its looking in <code>./basic/main.ts</code> while it should have been <code>./src/basic/main.ts</code>. Why is <code>baseUrl</code> not prepended? </p>
  
  <p>2) If (1) is fixed, the compiled files are not written to <code>./dist</code>. Why is <code>"outDir": "./dist</code> from the base file not used here? When I add the <code>outDir</code> to <em>tsconfig-basic.json</em> it works as expected</p>
  
  <p>Anyway, it looks like that extending here doesn't work, or works differently than I expect. Any suggestion how to improve my setup?</p>