Started this project because I wasn't happy with completion.sh that Bench ships with, or Click's auto completions due to how Frappe, Bench & external apps' commands work together. Currently we are working only on zsh completions. Mostly because it helps vastly during development.
Just copy pasting the following block in your zsh terminal and restarting your session should do the trick:
git clone https://github.com/gavindsouza/bench-autocomplete ~/.bench-autocomplete
cp ~/.bench-autocomplete/zsh/_bench /usr/local/share/zsh/site-functions/_bench
echo 'rm -f ~/.zcompdump; compinit' >> ~/.zshrc