Non-hierarchical subcommands / positional subcommands

[andreycizov]

Rust Version

rustc 1.32.0 (9fda7c223 2019-01-16)

Affected Version of clap

2.32.0

Bug or Feature Request Summary

I would like to be able to create a set an argument parsers for an utility that takes a list of commands to specify a list of input formats (let's call them IFs) and the set of commands that specify the output formats (OFs).

Currently, in order to do that I would need to create a whole tree of subcommands independently for each IF and for each OF. It doesn't seem to be an issue, but the output of --help would require to always specify at least one of the IFs in order to see the outputs of duplicated OFs in each of the IFs - that doesn't make for a user-friendly experience.

I come from python where argparse module allows you to do that: instead of specifying subcommands on the root parser - they simply return an instance of SubCommands that allows you to then specify the subcommands for that specific positional subcommand group.

Current Behaviour

Given IFs of xml, csv, txt and OFs of xml, csv, txt, the only way to specify those as subcommands would be (showing the output of the --help)

IFs help

>> convert --help
USAGE:
    convert [SUBCOMMAND]

SUBCOMMANDS:
    xml      desc_a
    csv     desc_b
    txt     desc_c

The going down to OFs:

>> convert xml --help
USAGE:
    convert xml [SUBCOMMAND]

SUBCOMMANDS:
    xml      desc_a
    csv     desc_b
    txt     desc_c

As is shown above, the output of every sub-sub-command would be the same regardless of what had been picked in the sub-command.

Expected Behavior Summary

>> convert --help
USAGE:
    convert [INPUT] [OUTPUT]

INPUT_SUBCOMMANDS:
    xml      desc_a
    csv     desc_b
    txt     desc_c

OUTPUT_SUBCOMMANDS:
    xml      desc_a
    csv     desc_b
    txt     desc_c

[epage]

I know its been a while since you've posted on this, so sorry about this.

I'm assuming that there are args specific to the input and output subcommands that you want specific ordering for and that is why you need to use subcommands rather than positional arguments with possible_values. Is that correct?

I come from python where argparse module allows you to do that: instead of specifying subcommands on the root parser - they simply return an instance of SubCommands that allows you to then specify the subcommands for that specific positional subcommand group.

Have an example? I've used argparse but not familiar with this functionality. I'm curious to see how other libraries handle this as this adds a certain level of complexity

[pksunkara]

Forget to tag this as related to #2222. Maybe even a duplicate?

[epage]

I think they are slightly different.

In #2222, the request is for the following to be equivalent

$ cmd start stop
$ cmd staet && cmd stop

While this would have

$ cmd xml --path ./in.xml xml --path ./out,.xml

If we applied #2222's reasoning, this would run the xml command twice but the request here is for the two xml commands to be different, with different args and behavior.

[epage]

btw if the main concern is the help output, the user can provide that directly. Maintaining that is annoying. #2913 and #2914 would allow custom dynamic help generation.

For now, I'm leaning towards that being our suggested route forward as this seems fairly specialized with a degree of its own complications. If there are concerns about that, let us know!