Is your feature request related to a problem? Please describe.
I'm always frustrated when I want to use program, and I press tab to see available options, but nothing is displayed, or it automatically selects files.

Describe the solution you'd like
I'd like to press TAB and see all available options

Describe alternatives you've considered

Additional context
Clap can generate completions using https://github.com/clap-rs/clap/tree/master/clap_generate, It's probably also possible when using structopt.