Suppress compiler warning "Supported source version 'RELEASE_6' from annotation processor... less than -source..." in picocli-codegen

[remkop]

picocli-codegen generates an (unnecessary) compiler warning that the annotation processor may not be forwards compatible with the version of Java that it is running on:

Supported source version 'RELEASE_6' from annotation processor 'picocli.codegen.aot.graalvm.processor.NativeImageConfigGeneratorProcessor' less than -source '1.8'

TODO: suppress this by adding this:

@Override
public SourceVersion getSupportedSourceVersion() {
    return SourceVersion.latest();
}

[remkop]

Fixed in master.