completion: add wrapper code to transform bash to zsh completion

[corneliusweig]

Cobra zsh completion is pretty broken. The idea is therefore, to use the working bash completion from cobra and wrap that with zsh adapter code. This code is based on the kubectl wrapper script.

I'm a bit unsure about the proper copyright notice. I left it as-is, but the beef of the logic comes from https://github.com/kubernetes/kubernetes/blob/master/pkg/kubectl/cmd/completion/completion.go . Must I therefore include a proper attribution for the wrapper script?

Fixes #1671

[codecov-io]

Codecov Report

Merging #1685 into master will decrease coverage by 0.2%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #1685      +/-   ##
==========================================
- Coverage   46.69%   46.48%   -0.21%     
==========================================
  Files         123      123              
  Lines        5600     5625      +25     
==========================================
  Hits         2615     2615              
- Misses       2716     2741      +25     
  Partials      269      269

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/completion.go	0% <0%> (ø)	⬆️
pkg/skaffold/build/docker/docker.go	11.86% <0%> (-5.21%)	⬇️

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[balopat]

Thank you for fixing this!!!

Must I therefore include a proper attribution for the wrapper script?

I think it's fine just as a reference to put a comment "inspired by kubectl completion script" and a link

[balopat]

On second thought - reading the Apache license maybe actually adding their copyright notice as attribution is not a bad idea. So in the end we would have

• skaffold copyright notice at the top as it is now
• then a comment describing that this is a derivative work of the kubectl wrapper with link
• then the copyright notice from the kubectl file

[corneliusweig]

@balopat Ok, I added the attribution to kubernetes. Is the go package path ok as a link?