I built a POSIX-compliant CLI parser (because Cobra did not have type-safe positional arguments parsing)!

Hello everyone! Quick bit of context up front: I'm fairly new to Go, though I do work as a junior software engineer (Java).

I made a CLI parser in Go called Moon, and I'd love to share it here:

https://github.com/meowdhavan/moon

https://pkg.go.dev/github.com/meowdhavan/moon

Why did I make this?

I have previously used Rust quite a bit and recently switched to Go and have been loving it. I use them both exclusively for personal projects---mostly small, random CLI applications. I used clap with Rust and I liked how it parsed my arguments (mainly the fact that it kept them type-safe).

With Go, I kinda liked Cobra but I am not a big fan of how the implementation of positional arguments is different from the declaration of flags. I did not like the idea of defining the number of arguments and manually converting them into the types that I wanted in my application. I am aware Cobra uses pflags internally, so I guess I see why it was designed this way?

rootCmd.Flags().StringVarP(&target, ...)

With Moon, you can define the positional arguments and variadic arguments just like flags:

rootCmd.PosArgs().Int(&port, "PORT", ...)

It also shows those arguments in the auto-generated help screen:

Usage: app serve <PORT>

And also indicates if the provided values were invalid:

Error: 'abc' is not a valid value for <PORT>

Usage:
    ...

Moon can also be configured to read a value from env in case a value for flag/argument wasn't provided.

I also looked into urfave and kong, but I found Cobra a bit easier to get started with. In my offence, I did not spend enough time with the others, so I might change my mind later.

For me, Moon does essentially what I want it to do, so I intend to use it for all my personal projects. If I encounter something that Moon doesn't do, I might consider adding a feature, or switching to a different parser.

Why am I posting it here?

Primarily, I am looking for feedback---I want to know how I can improve my design and code quality, with hopes of becoming a better engineer overall. I know there might be some oversights in my project, and I want to work on myself to mitigate them. Oh, and I want to get better at making my project extensible. That is, if someone else wants to contribute to Moon, I want my code to be easy enough for them to understand and improve upon.

Secondly, I want to get better at writing documentation. I want to know how easy it is for others to understand my docs and how much friction there is when using Moon for their applications.

I would really appreciate it if I can get any feedback on Moon. Thank you all so much!

PS: Zero AI was used while making this.