Support required flags

[blond]

Some options must always be specified.

I want to have a way to specify the required options in API.

Example

const cli = meow(`
    Usage
      $ process

    Options
      -i, --input   Input file
      -o, --output  Output file

    Examples
      $ process --input=lib/file.js --output=dest/file.js
`, {
    required: ['input', 'output']
});

A program without required options must quit with an error message.

$ process --output=dest/file.js

Missing required option:
    --input, -i  Input file

---

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Submitted pull Requests

• #110 Feat/add required flags
• #141 Implement isRequired feature as described in #51 and #110

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[kevva]

In most cases I would handle this in the API. Any reason you need to do it in the CLI?

[SamVerschueren]

I agree with @kevva. I believe this should be handled by the code that is called. That allows the most flexibility with informative custom error messages.

[kevva]

Going to close for now. If there are some good arguments for having this as an option we might re-open it again.

[sindresorhus]

I'm gonna reopen this as I think it could be useful for CLI only tools (ones that don't have an API).

It could be specified like:

flags: {
	rainbow: {
		type: 'boolean',
		alias: 'r',
		required: true
	}
}

We should be clear in the docs that API level option validation should be preferred.

The required option could also accept a function that could receive the arguments and do its own check whether it's required. For example, if the flag is only required when another flag is specified.

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[HackAfro]

If a required field takes a function, should the expected return value of the function be a boolean? A quick example could be helpful as I am currently working in this.

Thanks

[IssueHuntBot]

@HackAfro has submitted a pull request. See it on IssueHunt

[sindresorhus]

should the expected return value of the function be a boolean?

Yes

A quick example could be helpful as I am currently working in this.

{
	flags: {
		rainbow: {
			type: 'boolean',
			required: (input, flags) => flags.unicorn === '🦄'
		}
	}
}

Note, I'm not exactly sure what the function arguments should be. I'm open to suggestions there. I guess the input and flags. Anything else?

---

I also think we should call the option isRequired, not required.

[sindresorhus]

If anyone wants to work on this, see the previous attempt here and the feedback given: #110

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[NSExceptional]

Can we get this, but for input (non-flag arguments)?