tresata / scopt-auto

scopt-auto

Scopt-auto is an attempt to automatically create a scopt parser for a case class representing the target configuration.

The main ideas are:

• Parameters in the case class with default values becomes optional command line options. Parameters without default values become mandatory command line options.
• Nested case classes should be supported. This way these nested case classes can represent frequently re-used configurations without copy/paste.

The practical reality is:

• A camelCase parameter in a case class becomes a --snake-case argument.
• A parameter in a nested case class is represented by the dot notation (.) in the parser option. So for example config.nestedConfig.nestedSetting (config here is a value of our configuration case class) becomes the command line option --nested-config.nested-setting.
• Only one level of case class nesting is supported, simply because i couldn't find out how to do a second level using shapeless.
• To create a command line option that is optional without a default value use a case class parameter of type Option[T] with default value None.
• No Scala 3 support, we aren't using it yet...

A simple example:

scala> :paste
// Entering paste mode (ctrl-D to finish)

import com.tresata.scopt.auto.Options

case class Cpu(mhz: Int, cores: Int = 4)
case class Drive(size: Int, opal: Boolean = false)
case class Laptop(serial: Option[String] = None, cpu: Cpu, drive: Drive)

// Exiting paste mode, now interpreting.

import com.tresata.scopt.auto.Options
class Cpu
class Drive
class Laptop

scala> Options[Laptop].parse("--cpu.mhz 3000 --drive.size 2000")
val res0: Laptop = Laptop(None,Cpu(3000,4),Drive(2000,false))

scala> Options[Laptop].parse("--serial 123456 --cpu.mhz 2000 --cpu.cores 2 --drive.size 1000 --drive.opal true")
val res1: Laptop = Laptop(Some(123456),Cpu(2000,2),Drive(1000,true))

scala> Options[Laptop].parser
val res2: scopt.OParser[_, Laptop] = scopt.OParser@54812c74

scala> Options[Laptop].parse("--serial 123456 --cpu.mhz 2000 --drive.opal true")
Error: Missing option --drive.size
Try --help for more information.
java.lang.IllegalArgumentException: invalid arguments
  at com.tresata.scopt.auto.Options$$anon$1.parse(Options.scala:40)
  ...

scala> Options[Laptop].parse("--help")
Usage:  [options]

  --serial <value>      optional String
  --cpu.mhz <value>     required Int
  --cpu.cores <value>   optional Int (default 4)
  --drive.size <value>  required Int
  --drive.opal <value>  optional Boolean (default false)
  --help

Have fun! Team @ Tresata