i like know about the rust repo, how it is organized especially the cli interface
Clap is particularly powerful, and also has a macro option. You can define subcommands with it like a true champ.
This, however, doesn't answer the OP, since
rustc itself uses not clap, but getopts.
Getops is not as pretty as clap, but perhaps I misunderstood the question. I assumed the question was about what crate can handle command line arguments.