Updated bash/zsh function that cd to the root of git tree
This is looking great.  Thanks for incorporating the previous improvements and coming back for another round of review.  I noticed a few new things this time:

What does printf '%s' do for you that echo -n wouldn't?  Using printf when you're just passing through a string seems a little odd to me.  It should work either way, but printf would be more idiomatic for C where echo is much more common in shell scripts.
Adding the x constants in the comparison [[ &quot;x${git_root}&quot; != &quot;x./&quot; ]] are not needed.  Using the double square brackets deals with the disappearing variables.  You would need the extra x for [ comparisons because empty arguments become non-existant arguments which causes an error when you try to compare the non-existant to something.
I would use -n in the if [[ &quot;$super_root&quot; ]]; then line like so: if [[ -n &quot;$super_root&quot; ]]; then to make clear what you're trying to do there.