Add optional check for duplicated string and int type flags.

[arykalin]

Checklist

• [y] Are you running the latest v2 release? The list of releases is here.
• [y] Did you check the manual for your release? The v2 manual is here
• [y] Did you perform a search about this feature? Here's the Github guide about searching.

What problem does this solve?

Sometimes users can accidently duplicate string type flags and then the latest value we be taken. It is not clear and bad for usability.

Solution description

Add an option called Duplicated true\false to flag options. Example:

flagFoo = &cli.StringFlag{
	Name: "foo",
	Duplicated: false,
}

A detailed description of what you want to happen.

if Duplicated set to false command should fail with error
"flag foo can not be duplicated"

Describe alternatives you've considered

For now, as a workaround, we're using StringSliceType for flags we don't want to be duplicated and check that slice have only one element in it.

https://github.com/Venafi/vcert/blob/8e1dc13c0afdd615d7f27b80190ddf3a1d07e848/cmd/vcert/commands.go#L105-L120

[coilysiren]

Sometimes users can accidently duplicate string type flags and then the latest value we be taken. It is not clear and bad for usability.

Oh wow that sucks 😅we should definitely fix this 👍although possibly only in v3? Because I'm not sure if it would be considered a "breaking change"

[stale]

This issue or PR has been automatically marked as stale because it has not had recent activity. Please add a comment bumping this if you're still interested in it's resolution! Thanks for your help, please let us know if you need anything else.

[stale]

Closing this as it has become stale.

[dearchap]

Will consider for v3

[dearchap]

@arykalin If I understand correctly you've defined 2 flags(same type) with same name and only the last defined one will pick up values ?

[dearchap]

@arykalin Looking at your code you've defined "instance" as a stringslice flag and then enforced that if should not be length > 1 . Is this because if you've defined instance as a string flag and then people use the flag twice like --instance id1 and --instance id2 and then only the last value is taken. That is what you would like to guard against. ?