This pull request was largely inspired by this pull request: #11435

What I am trying to do differently here is to give plugin authors a way to define a command line interface for their sub-commands. This is accomplished by telling argparse in conda not to parse arguments for sub-commands it knows to belong to plugins.

This is accomplished by overriding the parse_args method on our custom ArgumentParser class:

https://github.com/travishathaway/conda/blob/9277f1e439f890bbbf557499d4045f646bb76034/conda/cli/conda_argparse.py#L228-L236

If it's a known plugin, we simply do nothing. Under the hood, it simply checks the value of sys.argv[1] to see if that string matches a name in our registered plugins list.

Later in do_call:

https://github.com/travishathaway/conda/blob/9277f1e439f890bbbf557499d4045f646bb76034/conda/cli/conda_argparse.py#L107-L113

We perform a naive check (maybe there's better way to do this?) to see that the args object doesn't have a func attribute. If doesn't we proceed to find the sub-command and execute its action callable.

Because this just calls a function without having parsed any arguments thus far, this leaves us free to do whatever kind of argument parsing we want. Below is an example program using click as the argument parser:

import click
import conda.plugins

__version__ = "0.1.0"

SUMMARY = "Example implementation of conda-doctor command"
SUBCOMMAND_NAME = "doctor"


@click.group()
def cli():
    pass


@cli.command(SUBCOMMAND_NAME)
@click.version_option(__version__, prog_name="conda-doctor")
@click.argument('param_one')
def command(param_one):
    print(param_one)


@conda.plugins.register
def conda_subcommands():
    yield conda.plugins.CondaSubcommand(
        name=SUBCOMMAND_NAME,
        summary=SUMMARY,
        action=cli
    )


if __name__ == '__main__':
    cli()

The click program needs to be setup as-if it was a program using sub-commands which is why we define a click.group. Otherwise, it works just like you would expect it.