What you're seeing is not bash tab completion based on compgen, but shell-mode's implementation of tab completion. Which is why git <TAB>, for example, does no

What you're seeing is not bash tab completion based on compgen, but shell-mode's implementation of tab completion. Which is why git <TAB>, for example, does not do what you'd like. It seems like it should be possible to write an emacs tab completer that actually calls bash's compgen, but I'm not aware of an implementation of this.