I never saw the need for annotating extension methods like in Lombok or Manifold . Lombok is great for other stuff though.
1. Without annotations you’ll be forced to index all static methods based on the first argument, globally.
2. Method call code completion will be ridiculous. How many static methods have String, File, List, Object(!) etc. as the first parameter? I don’t think anybody wants their code completion to be invaded like that.
The annotations provide intention. Essentially, adding an extension method is not something to be taken lightly, it requires careful consideration, weighing context, frequency, etc.