The language server uses reflection to provide things like hover hints for built-in classes like Channel. Method parameter names are not included by default in compiled Java code, but it should be possible to include them with the -parameters flag.

I tried it with this gradle config but it didn't work:

compileJava {
    options.compilerArgs << '-parameters' 
}

compileGroovy {
    options.compilerArgs << '-parameters' 
}

It compiled but then the hover hint was still incorrect:

Channel.of(arg0: T...) -> DataflowWriteChannel<T>

I probably just did something wrong in gradle, will come back to this later