title: TypeScript: Modify class before type checking
body: <p>I would like to implement a library similar to <a href="https://projectlombok.org/" rel="nofollow noreferrer">https://projectlombok.org/</a> in Java. For example, let's assume I'd like to implement a simple <code>@Setter</code> decorator that would add <code>setXyz()</code> methods for each field <code>xyz</code> in the class.</p>
  
  <p>Is this possible? e.g. compile-time decorators or a "plugin" to the compiler?</p>