feat: added clap shell completion and implemented Default trait on Args

[abhi-xyz]

• added build.rs: cargo will generate shell completion for bash, zsh, fish, nushell and elvish on source change
• implemented Default trait on Args: Now we can write tests without all those unnecessary args by replacing them with ..Default::default()

[thewh1teagle]

I'm wondering if it's possible to install the completions automatically when the program start. I don't see any mention about it in the clap_complete crate

[abhi-xyz]

Yep, technically its possible.

As developers, we usually bundle shell completions and man pages with the release assets, and it is the job of the package manager to place them in the appropriate directories. These directories vary across systems and shells. Even if we manage to determine the directories where shells automatically pick up completions, there are additional challenges, such as deciding whether to install them locally (user-specific) or globally (system-wide).

We generally leave these choices to the users or package managers. As far I have seen, it is the package manager that handles tasks like placing man pages and completion files in the correct locations during installation. I wouldn’t recommend trying to install completions manually within the program itself.

However, if you still want to handle it manually, you can include commands like these in an installation script:

mkdir -p ~/.local/share/fish/vendor_completions.d
cp completions/mc.fish ~/.local/share/fish/vendor_completions.d/

Each shell has specific directories where it automatically picks up completions without requiring users to source them explicitly in their configuration files. For example:

Bash: /usr/share/bash-completion/completions/ or ~/.bash_completion.d/

Fish: `~/.local/share/fish/vendor_completions.d

https://fishshell.com/docs/current/completions.html#where-to-put-completions