Regroup "similar" flags/options in the help prompt

[PandH4cker]

Please complete the following tasks

• I have searched the discussions
• I have searched the existing issues

Clap Version

3.0.0-beta.2

Describe your use case

Hi everyone,

I just suggest to add a simple feature about the display of the help prompt to regroup flags/options that seem to us "similar" and to simplify the help prompt in order to reduce its length and be more compact.

The function should regroup args and be visualized:

Like this:

--PS/PA/PU/PY <portlist>: help message

Instead of:

--PS <portlist> : same help message
--PA <portlist> : same help message
--PU <portlist> : same help message
--PY <portlist>  : same help message

Describe the solution you'd like

It could be nice to have a function like this:

impl<'help> App<'help>
pub fn help_regroup<T: Key>(mut self, arg_id: T, args: &[T], help_message: &str) -> Self

And be used like this:

app
     .arg(Arg::new("PA"))
     .arg(Arg::new("PU"))
     .arg(Arg::new("PY"))
     ...
     .help_regroup("PA", &["PU", "PY"], "Unique Help Message")

OUTPUT:

PA/PU/PY <value_name>: unique_help_message

### Alternatives, if applicable

_No response_

### Additional Context

_No response_

[epage]

To help understand the use case, how are the flags different if they have the same help message? Or is the flag name meant to be context enough to clarify, like a command dealing with semver versions have --major, --minor, --patch` flags?

[PandH4cker]

I mean by the same/unique help message including "or ..." in it like:

... : "Major or Minor or Patch.."

I'm building an app with Clap and I'm facing with this kind of "help duplicates" that could be nicer if more compact:

HOST DISCOVERY:
        --sL                                 List Scan - simply list targets to scan
        --sn                                 Ping Scan - disable port scan
        --Pn                                 Treat all hosts as online -- skip host discovery
        --PS <portlist>                      TCP SYN discovery to given ports
        --PA <portlist>                      TCP ACK discovery to given ports
        --PU <portlist>                      UDP discovery to given ports
        --PY <portlist>                      SCTP discovery to given ports

What It Should Be:

HOST DISCOVERY:
        --sL                                 List Scan - simply list targets to scan
        --sn                                 Ping Scan - disable port scan
        --Pn                                 Treat all hosts as online -- skip host discovery
        --PS/PA/PU/PY <portlist>             TCP SYN/ACK, UDP and SCTP discovery to given ports

[epage]

Some quick thoughts: I'd probably model this after usages to reduce user confusion. The downside is that would look like --PS <portlist> | --PA <portlist> etc which gets fairly verbose.