Tab completion for arguments

[Raymo111]

Background

Many command-line tools have tab completion (autocomplete) for arguments to simplify the user experience. i3lock-color currently does not. Tab autocomplete would make both testing and command-line usage easier.

Task

Add tab completion for arguments. To illustrate this, if I type i3lock --key<tab> then it should show me

--keylayout mode
--keyhlcolor=rrggbbaa

if I continue with l<tab> (i.e. now I have typed i3lock --keyl), I will get keylayoutautocompleted for me. That is, I will now have "typed"i3lock --keylayout`.

This enhancement is a nice and rewarding first issue, so if anyone wants to jump into i3lock-color/C/Linux development, this is a great starting point!

This seems like a nontrivial task:

• https://stackoverflow.com/questions/6107438/c-console-application-auto-complete-dynamic-arguments
• https://www.gnu.org/savannah-checkouts/gnu/bash/manual/bash.html#Programmable-Completion-Builtins