add FORWARD parameter type and stop parsing arguments when FORWARD is…

[Kamilcuk]

This change introduces a new click.FORWARD argument type, which stops the parser from further parsing arguments. Is it now possible to forward arguments without any parsing.
For example:

import click


@click.group()
@click.option("-v", "--verbose", is_flag=True)
def docker(verbose):
    pass


@docker.command()
@click.option("-v", "--verbose", is_flag=True)
@click.option("-u", "--user")
@click.argument("image")
@click.argument("command", nargs=-1, type=click.FORWARD)
def run(verbose, user, image, command):
    cmdline = ["docker"] + ([f"-u{user}"] if user else []) + ["run", image] + list(command)
    print(cmdline)


docker()

Allows for the following:

$ python ./docker.py -v run -u kamil alpine sh --help -u -v
['docker', '-ukamil', 'run', 'alpine', 'sh', '--help', '-u', '-v']

Issues:

• wrap sub CLI #1183
• --help doesn't get forwarded when using click.UNPROCESSED #556
• Support for docker like arguments termination #360
• Command to act as a proxy to another command #210
• Cannot ignore unknown options #489
• https://stackoverflow.com/questions/42457484/python-click-consume-options-as-arguments

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.

[davidism]

I'm not really clear what this does compared to adding a nargs=-1 argument, or using --. Regardless, I'm currently rewriting the entire parser, so this code won't be correct anyway.

[Kamilcuk]

or using --

It doesn't require it. See the attached issues.

docker run does not require --, you can run docker run alpine ls --help and get help for ls, not for docker. In contrast, that is impossible with click.

I'm currently rewriting the entire parser, so this code won't be correct anyway.

Ok, good luck! In that case, I will not fix the checklist.

I really hope that the new parser will not require -- to stop parsing. If it does, please let me know, I would want to invest time that it does not.

In any case, I use python3.7. I will back port this and publish on pip as I need it.

Thanks! Click is great, thanks for making it!