Merge cli flag modules in vlib to one

[danieldaeschle]

We have flag, cli and os.cmdline. All of them should be merged to one module.

https://discord.com/channels/592103645835821068/592320321995014154/789781987338485781

[dedesite]

Hi,
With @timbasel we try to address this issue.
There is a PR open only for discussion here : timbasel#1
I also created a gist which reflect how I see this "future" cli/flag module : https://gist.github.com/dedesite/1f1e26172729b022ef7833c934f8f0d8

I think before going forward, we need to be clear on what we want.

There has been discussion on discord with several contributor and here is the points were we seems to have found some sort of consensus :

• the module should accept -- and - for long flag syntax (ie -prod) but can encourage the first approach
• we can for example let the user create flag this way : name: "prod" and it will automatically become --prod.
• if the user want to have a single dash it could define the flag with : name: "-prod"
• Single letter flag should always be with a single dash
• No other flag syntax (like the DOS "/") should be allowed as even Microsoft doesn't recommend it
• they may be declared with an abbrev field or maybe as a array of name (ie `name: ["prod", "p"])
• The flag API is really neat because you can declare flag and retrieve their value in the same time :
  prod := fp.bool('prod', 0, false, 'Compile with optimisations.')
• cli declarative style "makes the structure of the cli inherently clearer" and separates the declaration from the parsing, but add several steps for retrieving flag values.
• we should have a way to define custom validator like eg:

	percent := git.get_float(cli.Flaf{
		name: 'percent'
		type_name: 'percent'
		flag: .custom,
		 validator: fn (value string) ?f64 {
			f_val := value.f64()
			if f_val >= 0 && f_val <= 100 { return f_val
			 } else { return error('Must be between 0 and 100')
			 }
		}
	})

• single letter boolean flag can be combine eg : rm -rf == rm -r -f
• flag can either be before argument or after. eg : v run test.v -prod == v run -prod test.v

If I come up with other thing, I will edit this message.

What do you think about that ?

[trollkarlen]

Can i suggest using the standard "--" and not "-" for multi char arguments.
This should be used on v itself also.
//T

[JalonSolov]

Using -- is a GNU standard, and has only existed as a "standard" since 1990. POSIX and many others that have existed for much longer (since the 1960s) only use - for all options, no matter the length.

[danieldaeschle]

To me follwing the newer standard makes more sense. :)

[JalonSolov]

Newer is not always better. And GNU is only 2 years newer than POSIX (1988), so not enough difference to matter.

[danieldaeschle]

Are there any arguments that one dash is better than two? Obviously most tools use two dashes and it's cleaner (to me).

[JalonSolov]

Yes, most GNU tools, but not most tools. Many common tools that come preinstalled only use single dash long options, like find, and lots of other tools you can get with your package manager of choice also only use single dash.

The ONLY time it is useful to use two dashes is if there are short options with the same first letter as a long option... assuming there are any short options at all. If not, it's just an extra character to type.

[trollkarlen]

Whats the take on this, no input since 2021 ?

[medvednikov]

Still needs to be done. Will do this year.

[daddycocoaman]

+1 for -- as the standard for multi-character flags.

[daddycocoaman]

Sorry. Documentation wasn't clear that this is what posix_mode on Command would do! Just found out.