Specifying types of default values for variadic args/flags

[iamkroot]

Question: Given spec,

option "--foo <foo>" default="bar" var=#true

What should the parsed type of foo be, assuming user didn't provide the flag on cli? (I believe the same question applies to arg/flag too)

Today, usage says the default is a string "bar" (so it literally sends a String type as parse output when user doesn't provide the flag on the CLI). But when user does specify --foo abc --foo def or even just --foo pqr, it suddenly becomes a multistring (["abc", "def"] or ["pqr"]). This creates a mismatch.

IMO, usage should consider var when deciding the types of default return values, and always return a vec in this case.

Now the question becomes, how do we specify a list of array values as the default in the spec. Reading KDL language spec, it seems the correct way would be-

option "--foo <foo>" var=#true {
    default {
        "xyz"
        "bar"
    }
}

In case the user only provides default="bar", we should convert it to a singleton array, ["bar"] so that it matches the runtime behavior in case the user does specify a single CLI arg.

Relevancy: While less important in shell scripts, this is extremely important to pin down for mise because the args are used in Tera, and we would like to support 1:1 mapping from usage MultiString to a Tera Vec<String>. See jdx/mise#7041

[iamkroot]

See also jdx/mise#4320 jdx/mise#4320

[jdx]

IMO, usage should consider var when deciding the types of default return values, and always return a vec in this case.

agreed

Reading KDL language spec, it seems the correct way would be-

I think that's the only correct way to handle multiple with kdl so it has to be that. That said, I think we should also support default="bar" but just make it parsed as ["bar"]. Reason being is that syntax is a lot simpler and a single default with var is rare—multiple defaults with var is extremely rare.

[iamkroot]

multiple defaults with var is extremely rare

Well, my current usecase is exactly that :)

I am writing a wrapper for a command, and would like to add something like --passthrough-flags option that just forwards these to the actual command. There's a bunch of "sane default flags" for this command (and the user can override them), so these need to be set in the usage spec.

I could go with passing all the flags as a single string arg, but then would have to deal with quoting/unquoting at various levels :/

[iamkroot]

But agreed on the default="bar" becoming an array.

[iamkroot]

Will try to get this implemented ASAP. Hopefully can be included in the next mise release

[jdx]

yeah my point was just that we don't have much of a choice with kdl around the syntax and I am also not terribly picky about the syntax here since I don't think it will be commonly used