Picocli: how to share options between parent command and subcommands

How to support shared options across all (or some) commands and subcommands? For example, if an end user provides --stacktrace anywhere in the command line arguments, any errors printed will include the stacktrace.

We can use a Mixin to define a boolean --stacktrace option, and include this Mixin in all (sub)commands, or use inheritance and let all commands subclass a class that defines a boolean --stacktrace option, but either way, that would define a separate boolean option for each command. Which option is true depends on where in the args the user put --stacktrace, so figuring out if --stacktrace was provided would mean iterating over all parent commands and seeing if any are true.

It would be nice to have a more convenient way to detect whether the user specified such a shared option.

Solution

Update: with picocli 4.3 there are two ways to accomplish this:

inherited options
let subcommands use a mixin that delegates to the parent command (so the state modified by the option is in one place)

One way to accomplish this is to make the boolean field static:

class Shared {
    @Option(names = "--stacktrace")
    static boolean stacktrace;
}

You would still need to either subclass or use a mixin to define this option in each command and subcommands:

@Command(subcommands = {Subcommand1.class, Subcommand2.class /*, ...*/}
class MyCommand {
    @Mixin
    Shared shared = new Shared();

    // ...
}

@Command(name = "subcommand1")
class Subcommand1 {
    @Mixin
    Shared shared = new Shared();

    // ...
}

The nice thing about this design is that there is now a single place where the application can detect whether the end user specified --stacktrace: the static boolean field:

public static void main(String... args) {
    assert Shared.stacktrace == false;

    MyCommand myCommand = new MyCommand();
    CommandLine.parseArgs(myCommand, "subcommand1", "--stacktrace");

    assert Shared.stacktrace == true;
}