Shell completion script for the builder

[fwilhe]

What would you like to be added:

It would be great if the builder had completion, reading out the actual available features in the current image being built.

For example in GL it should be like

./build k[tab][tab]
kvm

cf:
https://iridakos.com/programming/2018/03/01/bash-programmable-completion-tutorial

Why is this needed:

Developer experience would be better, both for seasoned contributors and for newcomers.

[Akendo]

Thanks for pointing me towards here. In general, I do not use shell. Instead, I would use complgen. I might take a look at this week.

[Akendo]

I've taken some time to understand a bit more how we're building our product and derived some more ideas to build up the completion. This works for fish more well now:

[Akendo]

I'm currently unable to perform proper subword matches after defined the platform. I've created an issue with the project , but I might do something wrong here. If this is not going to get address until EOW, we might close this down and move on to more important tasks.

[Akendo]

The problem was resolved. Thanks to @nkraetzschmar for pointing to my error. We have now a working MVP for bash.