Include in program usage printout the default values of the options.

[jorgeluismireles]

Describe the feature

When using flag module and your program is running with help -h we need the program print the default values of the options. The users need to know what are the parameters default values they will not provide.

Use Case

https://play.vlang.io/p/eec968e1a6

import os
import flag

fn main() {
	mut fp := flag.new_flag_parser(os.args)
	fp.application('MyApp')
	fp.version('0.0.1')
	fp.description('My app is good')
	fp.skip_executable()
	param := fp.int('parameter', `p`, 34, 'My parameter')
	_ := fp.finalize() or { panic('${err}') }
	println('${param}')
}

If you run the above program it will print the default value of `param which is 34:

34

But if you run your program with -h the program prints the usage and exit:

MyApp 0.0.1
-----------------------------------------------
Usage: MyApp [options] [ARGS]

Description: My app is good

Options:
  -p, --parameter      My parameter
  -h, --help                display this help and exit
  --version                 output version information and exit

The playground prints the above if you set the page above textfield Run arguments with -h.

The issue is that line -p, --parameter My parameterdoes not include (as Golang does) the default value of this parameter.

Proposed Solution

In the printout, changes lines like this:

-p, --parameter      My parameter

into this:

-p, --parameter      My parameter (default 34)

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

Version used

V 0.4.8 e61475e

Environment details (OS name and version, etc.)

Playground

_{Huly®: V_0.6-21418}

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