Writing custom Lombok Annotation handlers

In the meantime Reinier Zwitserloot created a new git-branch sclExpansionUpdate, that contains an updated version of the ShadowClassLoader:

ShadowClassLoader is now friendlier to trying to extend lombok.

Your (separate) jar/dir should have a file named META-INF/ShadowClassLoader. This file should contain the string 'lombok'. If you have that, any classes in that jar/dir will be loaded in the same space as lombok classes. You can also rename the class files to .SCL.lombok to avoid other loaders from finding them.

I guess this did not yet make it into the main branch because it certainly has not been tested that much - I just tried it out for myself and it contains a little bug that prevents loading the required META-INF/services from extensions. To fix it you should replace two method calls to partOfShadow with inOwnBase:

[... line 443]
Enumeration<URL> sec = super.getResources(name);
while (sec.hasMoreElements()) {
    URL item = sec.nextElement();
    if (!inOwnBase(item, name)) vector.add(item); // <<-- HERE
}

if (altName != null) {
    Enumeration<URL> tern = super.getResources(altName);
    while (tern.hasMoreElements()) {
        URL item = tern.nextElement();
        if (!inOwnBase(item, altName)) vector.add(item); // <<-- AND HERE
    }
}

I tested it with the above fix and it seems to work fine (not tested much though).

On a side note: with this new extension mechanism, it is now finally also possible to have the extensions annotation handlers and annotations in a different namespace than "lombok" - nice!

Using the input from this question and from the other answer (by Balder), we managed to put together a custom Lombok annotation handler: Symbok. Feel free to use that as a sample for writing your own.

BTW, instead of writing a custom Lombok handler, you could also implement a javac plugin instead -- it might be simpler.