Provide a way to create standardized Option libraries.

[mimendo]

Hello,

I am looking for an easy way to standardize options so that everyone uses the same options for the same purposes.
What I was thinking is something like this:

@Output
private Path output;

Where @Output is @Option(names = {"-o, --output"})

To achieve this, I would like to do something like this:

@Option(names = {"-o", "--output"})
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER, ElementType.ANNOTATION_TYPE})
public @interface Output {
}

For this to work, I would need the @Option annotation to also have the target ANNOTATION_TYPE (note that my @Ouput definition also has this target to make it recursive).
And, of course, the CommandLine should search for annotations recursively (unless you know a better way to achieve the same result).

This could be an exciting feature, and I would happily provide a pull request.

Let me know what you think :)
Picocli is great! Thanks for it!

[remkop]

Hi @mimendo, I would have added ElementType.ANNOTATION_TYPE to the Option annotation, but I want picocli to be binary compatible with Java 5 and later, and the ElementType.ANNOTATION_TYPE was introduced in Java 8, unfortunately.

[mimendo]

Ok, I overlooked that compatibility requirement. I've seen a folder for Java 9, probably just for module compatibility, but I hope I will soon see a Java8 (or later) based version of Picocli. In the meantime, I think I will choose the "add as source" option and modify it to suit my needs, if that's acceptable to you.