It's possible to set up autocompletion after brew install git-extras semi-automatically.

[spacewander]

Original discussion: #1101

I learned today that we can set up the completion script via brew. Here is an example:
https://github.com/Homebrew/homebrew-core/blob/7f1cee678803c55daa0d826222437184e56b4231/Formula/k/kubectx.rb#L22
https://github.com/ahmetb/kubectx/tree/master/completion

Some manual configuration is still required: https://docs.brew.sh/Shell-Completion