Extract submenus into a new project

[kotfu]

The submenu feature is nice, but it's very complex. What if we extracted the submenu code into a new GitHub project at https://github.com/python-cmd2/cmd2-submenus, and packaged it in pypi as a separate wheel, something like cmd2-submenus. This would enable:

1. Easier maintenance of the core cmd2 module
2. Version dependency between releases of cmd2 and cmd2-submenus. If cmd2-submenus lags behind cmd2 features, users of both modules can make a decision whether they want to most current cmd2 capabilities, or submenu support.
3. Set a pattern for extensibility of cmd2 via additional packages instead of changes to the core.

I'm willing to take a crack at the extraction of the submenu code if there is interest in pursuing this proposal.

[kmvanbrunt]

What about the submenus not having access to self.command_parser?

[tleonhardt]

I like the idea of extracting the submenu code into a new GitHub project underneath the python-cmd2 organization.

Easier maintenance for the core of cmd2 would be welcome. But with being able make cmd2-submenus require a certain version of cmd2, we could still maintain the Submenu feature, albeit at perhaps a somewhat slower pace.

I also like the concept of setting a pattern for extending cmd2 via additional packages. Features may come along which are very desirable for a certain subset of users which may not feel appropriate to incorporate within the core cmd2 module and/or may add additional 3rd party dependencies which we don't want to levy on the core cmd2 module.

[kmvanbrunt]

@kotfu
What version of cmd2 will this be tied to? You and I both have bugs where the submenu does not have access to a parent's attribute. In fact, starting with 0.8.4, submenu tab completion has been broken because of this.

[tleonhardt]

I would say tie it to the last version of cmd2 where the Submenu feature worked well.

[kmvanbrunt]

I think I was able to fix both of the submenu issues with tab completion. I'll create a PR soon. Hopefully this will help with @kotfu's issue, too.

By the way, I still support the idea of moving submenus to its own project.

[anselor]

@kotfu @kmvanbrunt
Since it appears there are easy fixes for submenus we should probably just patch it up as is in 0.8.X.

As for the 0.9.X branche, I have an alternate idea for submenus. I think it's possible to present subcommands (argparse sub-parsers) in a way that it looks like submenus.

Commands using argparse can be decorated to indicate they want to present as a submenu. When one of these commands is processed, we can save it and flag that we're navigating down a particular command. Help and tab completion would then only present that command's subcommands. If there are more layers of subcommands, that would get pushed on to the command navigation stack and the next layer of subcommands would be available. When executing a command, we can automatically prepend the preceding layers command/subcommands before parsing the command.

Command history can be separately maintained when we go into this state just like with submenus today.
the shared attributes stuff from the current implementation wouldn't be needed because everything would be running in a single Cmd instance.

[tleonhardt]

@anselor
If you think the approach you discuss is viable and not too difficult to implement, then from an architectural perspective I like it a LOT better than the current approach which involves nested cmd2.Cmd instances.

[anselor]

I'm also pretty sure this could be done as a specialized subclass of cmd2.Cmd so it doesn't need to be part of the base implementation.

[kotfu]

I've extracted the submenu code into a new project at https://github.com/python-cmd2/cmd2-submenu. There is a new branch here extract_submenu with the submenu code deleted. The new submenu project isn't quite working yet, but I'm pretty sure I can make it happen.