Type checking and other features not working with Gradle project

I used this extension to work on a Maven project originally, and it worked very well. The main features I'm interested in are type-checking (getting a warning if I call a method with bad arguments, or if I call a method that doesn't exist, say) and import warnings (being told I need to import something before using it, and being able to add the import with a single click).

Now I'm working on a Gradle project (an Android project), and these features no longer work. When I open the developer console, I see this type of error every time I open a .java file:

Error: src/main/java/com/google/android/exoplayer/demo [in demo] is not on its project's build path

Environment

• Operating System: Ubuntu 18.10
• JDK version: 1.8
• Visual Studio Code version: 1.31.1
• Java extension version: 0.39.0

Comienza reproduciendo el error reportado al abrir un archivo Java en el proyecto Android basado en Gradle, usando los detalles del entorno indicados en el issue. Rastrea cómo se detecta la ruta de compilación del proyecto y compárala con el caso funcional de Maven; se considera terminado cuando la comprobación de tipos y las advertencias de importación funcionan sin el error de la ruta de compilación.