Feature request: mark a flag as deprecated or retired

[nevion]

While maintaining a program that accepts CLI flags, one often wants to deprecate an option - still leaving it functional but providing a warning to the user, or retiring an option, meaning the flag is consumed but otherwise ignored.

Any thoughts on what that functionality could look inside CLI11?

[phlptp]

I can think of a couple approaches. One would be to add a deprecated flag, but that would add overhead on every option in terms of size and checking a flag. Probably not a lot but some.

The other options would be to add a wrapper function like deprecate_flag(app, flag_name) which goes through and modifies the description and injects a custom each function which prints out a deprecated message if the argument is used but otherwise does nothing.

A retired function could be similar but would probably need to replace the callback so it does nothing instead of the original callback.

Some advantages and disadvantages to both approaches. I could see it being a useful thing to have available though.

[jbriales]

This is a very interesting request :)
I'm wondering what would be the case for deprecating an option name rather than the whole option.
I.e. if the option gets multiple names like "--foo,--bar" and you want to deprecate one of the names only.

[phlptp]

I suppose I could see if you were wanting to shift the format conventions of a long form option to be consistent with other parts of a program, then you may only want to deprecate one of the names.

Though by far most of the use cases I might want this for would apply to the whole option. So in #358 I was only dealing with whole options.