Clap custom help text

[Spatenheinz]

I am using cla 4.5.1 and have two questions:

1. In the Commands::help_template is it possible to make
   underlining of words such as done for the default tags like: {usage-heading}?

2. Is it possible to flatten or inline optional arguments, so they are show like:

cmd [--option1] [--option2]

instead of

cmd [OPTIONS]

Options:
option1
option2

Any help is appreciated.

[epage]

In the Commands::help_template is it possible to make
underlining of words such as done for the default tags like: {usage-heading}?

help_template accepts a StyledStr. This means you can use ANSI escape codes to style it as much as you want.

Is it possible to flatten or inline optional arguments, so they are show like:

Not at this time.

The collapsing is done to prevent problems like

usage: git [--version] [--help] [-C <path>] [-c <name>=<value>]
           [--exec-path[=<path>]] [--html-path] [--man-path] [--info-path]
           [-p | --paginate | -P | --no-pager] [--no-replace-objects] [--bare]
           [--git-dir=<path>] [--work-tree=<path>] [--namespace=<name>]
           [--super-prefix=<path>] [--config-env=<name>=<envvar>]
           <command> [<args>]

As there aren't usually too many positionals, we switched to unconditionally showing all of them in #769.

The challenge for options is finding an appropriate way to decide what to not collapse. #4191 would have an opt-in for groups in splitting usages.

Our options

• Have an opt-in setting on Arg
• Expose the usage generation mechanism and let people provide their own usage impl, wrapping ours, that does this to their desire