Help: Cmdliner mutually exclusive argument that is a string

Learning
1

I need add a mutually exclusive argument that is a string using Cmdliner lib.

Example

./program --suppress dir_a,dir_b

## or

./program --unsuppress dir_a,dir_b

The examples I found take a boolean indicating which argument was used, but beyond that I need the value.

open Cmdliner

let suppress_unsuppress =
  Arg.(
    value & vflag None
    & [
        ( Some true,
          info
            ~doc:
              "Don't report on files whose path has a prefix in the list. \
               Comma-separated-path-prefixes"
            ["suppress"] );
        ( Some false,
          info ~doc:"Report on files whose path has a prefix in the list"
            ["unsuppress"] );
      ])
in
2

Couldn’t you supply both flags at the same time if they specify disjoint sets of prefixes?

I would approach that behavior by adding a validation step after the args had been parsed that ensures the sets of prefixes are disjoint.

3

Maybe you have no choice how to design the flags but if you do, here are some alternatives:

  • make suppress and unsuppress` sub commands (like in Git), which is supported by Cmdliner.
  • make one behaviour the default and use just one flag to revert to the other. This is what commands like gzip do.
4

You can make that work at the Term level.

Here’s an example: 4 mutually exclusive arguments, which are assembled into a single term that checks for exclusivity.

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