Optional type and Custom option processing do not work together

[prodigitalson]

Opening a new issue exactly the same as #984.

I have a use case for a where I would like a flag with an optional value, however instead of the flag being true I want to evaluate it to a default value.

Ideally the following would happpen:

program
  .option('-w, --with-cheese [value]', 'Use something special', 'cheddar');

program.parse(process.argv);

if (program.withCheese) {
  console.log(`You ordered a sandwich with ${program.withCheese} cheese`)
} else {
   console.log(`You ordered a sandwich`);
}

$ sandwich
You ordered a sandwich
$ sandwich --with-cheese
You ordered a sandwich with cheddar cheese
$ sandwhich --with-cheese provolone
You ordered a sandwich with provolone cheese

That seems like it could lead to unexpected and ambiguous results though. So the next best thing, and how i immediately thought to handle it, was with custom option processing:

const defaultIfTrue= (defaultValue) => {
  return (curr, prev) => curr === true ? defaultValue : curr;
}
program
  .option('-w, --with-cheese [value]', 'Use something special', defaultIfTrue('cheddar'));

program.parse(process.argv);

if (program.withCheese) {
  console.log(`You ordered a sandwich with ${program.withCheese} cheese`)
} else {
   console.log(`You ordered a sandwich`);
}

However given the details in #984, this doesn't work either. I'm investigating the event listener, but I can't/don't want to store something outside of the normal options, meaning I need to update the command so that program.withCheese AND program.opts().withCheese reflect the value appropriately. I have yet to figure that out...

[shadowspawn]

I expect you are looking for a more sophisticated solution, but I'll point out there is a simple manual approach to handling the default value in the README:

if (program.cheese === undefined) console.log('no cheese');
else if (program.cheese === true) console.log('add cheese');
else console.log(`add cheese type ${program.cheese}`);

[shadowspawn]

(On a historical note the default value in this case is being treated the same way as for an option with a required value, rightly or wrongly, and has been that way since the beginning:

• commander.js/index.js

  Line 420 in d5186ba

  // preassign default value for --no-*, [optional], <required>, or plain flag if boolean value

• commander.js/index.js

  Line 317 in 2a21655

  // preassign default value only for --no-*, [optional], or <required>

  
  )

[shadowspawn]

I had been wondering whether the custom option processing function should be called when there is no value for an optional flag. This would allow more complex handling like in the original post in this thread, but I realised today would break the use of simple coercion routines.

program
  .option('-f, --float [value]', 'coerce value to float', parseFloat)

The current behaviour is calling the program like foo -f will set the value to true. If parseFloat was called it would instead be set to NaN.

[shadowspawn]

An approach was provided, and no further activity in a month. I have had a look at the code history, and discounted one possible code change. There is not likely to be further action due to this report.

Feel free to open a new issue if it comes up again, with new information and renewed interest.

Thank you for your contributions.

[shadowspawn]

I discovered recently that options with optional arguments are actually broken when there is a default value, making the requested behaviour difficult to achieve. The option is ignored when supplied without a value.

I have PR #1652 open to fix that, and add .preset(), which works well for the requested behaviour.

program
  .addOption(new Option('-w, --with-cheese [value]', 'Use something special').preset('cheddar'));