Add auto completion for loco and cargo loco commands

[andreystepanov]

Feature Request

Is your feature request related to a problem? Please describe.

Currently there's no auto completion for CLI commands, and it would've been nice to have them. Especially for more complex commands such as:

cargo loco generate scaffold posts name:string title:string content:text ... --api

Describe the solution you'd like

I'm not sure if it would be possible to auto-generate them on the fly though, since there's a build step for cargo loco ... subcommand.

Maybe instead we can introduce loco completions [bash|zsh|fish|nushell|...] subcommand, that will output statically defined completions for specified shell.

Describe alternatives you've considered

Alternatively, all necessary auto completions can be contributed to designated repositories and later linked back in the documentation website somewhere in Installing section.

Here's my contribution to nushell/nu_scripts#1029, for those who uses Nushell.

[jondot]

Hi @andreystepanov it sounds like you are experienced in this. Would you like to submit a PR that implements such completions? It also may be that clap has a feature flag for supporting some of it.

[andreystepanov]

Yes, sure!

I have a few questions though:

1. How stable the cargo loco subcommands and their flags are? Do you forsee any major changes, or it's more or less complete (from end-user perspective)?

2. What is the source of truth for attribute types that can be used in cargo loco g (model|scaffold|migration) posts field:* subcommands?

I can see there's a loco-gen/src/mappings.json, but attributes defined in there are different from what user can see on the website.