How to customize launcher script's -h output to include my application's own options?

[alexeyr]

I would expect this to be a common requirement, but couldn't find it in http://www.scala-sbt.org/sbt-native-packager/archetypes/java_app/index.html.

[muuki88]

Thanks for your feature request, but I think this feature is out of scope for native packager.

The command line options are for the start script alone. I can't see the advantage in defining your cli options in the bash script and in your application. If you use scopt or finagle flags you will get parsing, validating and help messages all in one.

[alexeyr]

That's precisely it: if the users pass -h or -help, they get one set of options; if they pass --help (or perhaps -- -h), they get another. And the usage message of the start script can't tell them about --help.

[alexeyr]

I definitely wouldn't want to define the options in two places.

[muuki88]

So a more helpful help message from the bash start-script would at least ease this confusion? There is a friction between the built application and the default start script. I'm not sure how we could close this gap in a user friendly and easy way.

[alexeyr]

Yes. One approach I thought of is to have an SBT setting telling sbt-native-packager what arguments to pass for usage information. If it's e.g. Some("--help"), <start-script> -h ends with printing Usage message for the application: and then calling <java-command> --help.

[muuki88]

Yeah, that would be possible, but can get tricky.

1. Custom mainClass definitions must be taken into account when processing the app args
2. What usage is printed on an invalid input?
3. What happens with non-parsed inputs?

I'm not saying this is not possible, nor not useful. My main concern is making the bash-script more complex that it already is. If the "usage printing logic" can be optionally plugged in, then this would be nice, but I fear this is not simple possible either.