Configuring multi-value defaults in list option in tz example

[remkop]

Hi Max, congrats again on jbang, nice work!

The tz example mentions some difficulty with configuring defaults for multi-value options.

It is possible in picocli to configure default values for a multi-value option, if you are willing to allow comma-separated values. You would do that by setting the split = "," attribute in the @Option or @Parameters annotation. Then you can set multiple default values in a single string:

@Parameters(split = ",", defaultValue = "1,2,3") List<Integer> myNumbers;

Similarly for tz:

class ListDefaults {
    @Parameters(split = ",",
            defaultValue = "America/Los_Angeles,America/Detroit,Europe/London,Europe/Zurich,Asia/Kolkata,Australia/Brisbane",
            description = "Time zones. Defaults: ${DEFAULT-VALUE}.",
            hideParamSyntax = true, paramLabel = "[<zones>[,<zones>...]...]")
    List<ZoneId> zones;

    public static void main(String[] args) {
        ListDefaults instance = CommandLine.populateCommand(new ListDefaults()); // without args
        System.out.println("ZoneIds are: " + instance.zones);

        System.out.println();
        System.out.println("It makes the parameter label in the usage help a bit verbose though...");
        System.out.println("So we set a custom label.");
        System.out.println();
        new CommandLine(new ListDefaults())
                .setUsageHelpLongOptionsMaxWidth(30) // requires picocli 4.2
                .usage(System.out);
    }
}

[maxandersen]

ah that’s nice - what happens if you mark such parameter arity="0..*" ...would it be possible to mix-match comma separated vs spaces or does that end up being a List<List<ZoneId>> ?

[remkop]

You don’t need to specify arity.
The parser will accept both comma-separated and individual values.
It should just work. You won’t end up with nested lists.

[maxandersen]

not sure what I do wrong but I get an empty list on start, even tried upgrading to 4.2.

the parameter parsing works though as it does work with tz.java 15:00 cet,bdt ist where it detects all three.

but if just done as tz.java 15:00 nothing is print out as if just empty list.

[remkop]

Can you push your code on a branch where I can take a look at it?

[maxandersen]

#56 has the change - copied verbatim from your example + converter attribute (which does not seem to make a difference for this behavior).

With that pr tz.java 15:00 prints out nothing as if timezones are not specified.

[remkop]

OK, I found the problem. The timezones option needs to be defined like this:

@Parameters(index = "1..*", split = ",",
        converter = ZoneIdConverter.class, // <.>
        defaultValue = "America/Los_Angeles,America/Detroit,Europe/London,Europe/Zurich,Asia/Kolkata,Australia/Brisbane",
        description = "Time zones. Defaults: ${DEFAULT-VALUE}.",
        hideParamSyntax = true, paramLabel = "[<zones>[,<zones>...]...]")
List<ZoneId> zones;

Note the index = "1..*" part. This was missing, so both parameters were looking at index zero (the first argument). Picocli does not automatically increase the index when multiple @Parameters are defined. This is a tricky area (see for example remkop/picocli#564).

Anyway, adding the index bit will fix it.

One thing: I found this by switching on picocli's built-in debug tracing. I ended up changing the source code of the tz main method to do this, because I could not figure out how to pass -Dpicocli.trace=DEBUG on the command line. I tried these:

remko@LAPTOP-7EO0MTL0:/mnt/c/Users/remko/IdeaProjects/jbang$ jbang -Dpicocli.trace=DEBUG examples/tz.java 15:00
Unknown option: '-Dpicocli.trace=DEBUG'
Usage: jbang [-eh] [--verbose] [--version] [--clear-cache] [--completion]
...

and

remko@LAPTOP-7EO0MTL0:/mnt/c/Users/remko/IdeaProjects/jbang$ jbang examples/tz.java -Dpicocli.trace=DEBUG 15:00
Unknown option: '-Dpicocli.trace=DEBUG'

In both cases, picocli is parsing the option and treats it as an application option: first of the jbang application, and next of the tz application. It may be worth treating -Dx=y options to jbang as special and pass them as VM parameters.

[maxandersen]

thanks for the info, just pushed fixed to master and you gave me the idea to implement support for implementing -D passthrough :)