Including `transform:` parameter in `@Argument` declaration generates wrong help message for optional arguments

[YourMJK]

Declaring an argument with @Argument(..., transform:) makes it non-optional in the "USAGE" and doesn't include it's default value in the argument's abstract in the "ARGUMENTS" section, even if the value has a default value and/or is of an optional type.
(The actual parsing of the optional arguments seems to be correct)

ArgumentParser version: 1.1.3
Swift version: swift-driver version: 1.26.9 Apple Swift version 5.5.1 (swiftlang-1300.0.31.4 clang-1300.0.29.6)

Checklist

• If possible, I've reproduced the issue using the main branch of this package
• I've searched for existing GitHub issues

Steps to Reproduce

Declare arguments like this in a ParsableCommand struct:

struct Cmd1: ParsableCommand {
  @Argument(help: "Test argument 1", transform: { Int($0)! })
  var test1: Int = 0
  
  @Argument(help: "Test argument 2", transform: URL.init(fileURLWithPath:))
  var test2: URL?
}

and print the help message through Cmd.parseOrExit([]) or print(Cmd.helpMessage())

Expected behavior

The printed help string (namely USAGE and ARGUMENTS) should be the same as if the arguments were declared like this (without the transform: parameter):

struct Cmd2: ParsableCommand {
  @Argument(help: "Test argument 1")
  var test1: Int = 0
  
  @Argument(help: "Test argument 2")
  var test2: String?
}

Actual behavior

Help message for arguments with transform: parameter looks like this:

USAGE: cmd1 <test1> <test2>

ARGUMENTS:
  <test1>                 Test argument 1
  <test2>                 Test argument 2

While help message without transform: is correctly generated:

USAGE: cmd2 [<test1>] [<test2>]

ARGUMENTS:
  <test1>                 Test argument 1 (default: 0)
  <test2>                 Test argument 2

[rauhul]

Hey @YourMJK this is actually working as intended. By using transform you opt out of using ExpressibleByArgument which means you lose out on the default value getting printed. However while investigating the issue I did find a number of other help generation bugs which I have included in 477.

[YourMJK]

Thanks for the response.

This doesn't make much sense to me and I'm not sure if it's working as intended.
To clarify, I'm talking about the usage string that's being generated.

I would expect that declaring any argument of an optional type like this:
var arg0: T?
to produce a usage string like this:
USAGE: cmd [arg0]
regardless of whether a transform closure is specified or not.

This is currently not the case. Instead it's
USAGE: cmd <arg0>

I don't understand why I can't have an optional argument when I specify the transform closure.
I can't see any technical reason that would make it impossible to implement this (IMO expected) behavior.

[rauhul]

Sorry I misspoke, you are correct that the "Optionality" of the argument should be preserved regardless of transform vs ExpressibleByAgrument. I meant to say that the (default: 0) will not occur for the transform path.

[YourMJK]

I see, thanks for the clarification.

[rauhul]

Give main a try, the bug should be resolved!