Additional parameters for coercing functions

[vonagam]

If you want to throw an error in a coercing function because a received string value does not satisfy some requirement you might want to have access to an option name (or a command name) to customise an error message.

How about changing coerce signature?

// from
(value: string, previous: T) => T
// to
(value: string, previous: T, option: Option, command: this) => T

One will be able to use long, name() or attributeName() from Option to customise a message. Also negate property is useful. None of those are accessible right now.

command can be used to get its name for an error or currently parsed options if a person wants to change coercing behaviour based on already present options. User already has access to command, so nothing new in terms of access, just convenience.

[shadowspawn]

This is an interesting suggestion thanks, and aligns with the name shortcoming I noticed when I was writing a custom validator recently: #518 #1130

Fair warning though, we are not going to rush a change. The previous changes to the parameters for the coercion function caused a lot of problems, in particular by breaking parseInt: #943 (The next change should hopefully be less problematic!)

The support for a RegEx to validate the option values has been removed from the documentation as underdelivering, and I commented there I thought the custom option processing was a better longterm approach: #967

Providing an array of allowed values for an option (#518) is one of the two most upvoted open issues.

Interested in seeing interest in this, and whether it looks a good approach for allowing the custom option processing to solve questions that come up.

[shadowspawn]

There will be more possibilities in Commander v7, with one coercing function moved down into the Option: #1331

This issue has not had any activity in over six months. It isn't likely to get acted on 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.