I have posted a single line explanation here I thought these steps were trivial, So didn’t include any instructions.
It is too slow as of now though. It actually executes the python script (in this case bench itself) upon setting a magic environment variable to generate suggestions.
I’ve observed how other command line utilities do this, e.g. git. It’s a little painful to write and update a shell script for completions (instead of a click hack) which is somewhat necessary to improve the speed.
I’ll (probably) soon provide you with a faster completion method.