Swap from YAML Clap CLI to derived struct Clap CLI

[seblund]

YAML in Clap has been deprecated and we were two major versions behind. This PR changes the CLI to be derived from a struct and it is much cleaner IMO. We are now on the newest version of Clap which resolves #143.

Before, we had a very flat structure as we had no subcommands, e.g. you could technically supply a query, an input-folder, and give the -p argument to start the server at the same time as they were all optional.

I personally think this resulted in a very confusing user experience from the terminal, having all arguments be contextually optional is a bit strange as running a single query and starting a server are two very different. It would be nice if they are separate.

In this PR there are two subcommands serve and query:

This is nice because we can avoid a bunch of the optional arguments. E.g. if you are starting a server, you can only supply the ip, port and other relevant arguments, not an input folder and so on:

And we can provide contextual examples for the subcommands without overwhelming the user from the beginning:

If we prefer the flat structure of the CLI from before it is a very quick change, so discuss here what you prefer :)

[andreaskrath]

I would suggest adding some test cases to the new CLI structure to ensure arguments are matches correctly.

The Parser trait from clap has a parse_from associated function which matches arguments from the supplied parameter; the parameter must implement the IntoIterator trait and its items must implement the Into<OsString> trait - which a string vector already does. The parse() associated function from the Parser trait uses this function underlying, and simply supplies the arguments via std::env::args_os().

As such, you can test the CLI structure by creating string or string slice vectors and use the parse_from associated function, to ensure correct argument matching.

Look at https://docs.rs/clap/latest/clap/trait.Parser.html for more info about the Parser trait.

Provided and example based on some of the screenshots you linked in your pull request.

#[test]
fn serve_command_with_t_and_c_flags() {
    // 0th argument does not matter, but it must be present
    let input_args = vec!["", "serve", "-t", "1", "-c", "50", "127.0.0.1:4242"];
    let args_matches = Args::parse_from(input_args);
    match args_matches {
        Args::Serve {
            endpoint,
            thread_count,
            cache_size,
        } => {
            assert_eq!(endpoint, "127.0.0.1:4242");
            assert_eq!(thread_count, 1);
            assert_eq!(cache_size, 50);
        },
        _ => unreachable!(),
    }
}

The primary purpose behind this would be to ensure the CLI is not mistakenly broken at some point, if further changes are made to it.