> Related question: what would it take to add a zsh completion sanity
> check to t/t9902-completion.sh?

I don't know.  What I do know is that we can't just run our tests with
ZSH, e.g. running 'zsh ./t0000-basic.sh' shows mostly failures.  So it
won't be as simple as modifying 't/lib-bash.sh' to somehow support ZSH
as well.

> Here's a minimal fix, untested.  As a followup, as Gábor suggests at [2],
> it would presumably make sense to stop overriding ZSH_VERSION, using
> this GIT_ scoped variable everywhere instead.
> 
> Thoughts?
> 
> Reported-by: Rick van Hattem <wolph@wol.ph>
> Reported-by: Dave Borowitz <dborowitz@google.com>
> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
> 
> [1] https://public-inbox.org/git/01020163c683e753-04629405-15f8-4a30-9dc3-e4e3f2a5aa26-000000@eu-west-1.amazonses.com/
> [2] https://public-inbox.org/git/20180606114147.7753-1-szeder.dev@gmail.com/
> 
> diff --git i/contrib/completion/git-completion.bash w/contrib/completion/git-completion.bash
> index 12814e9bbf..e4bcc435ea 100644
> --- i/contrib/completion/git-completion.bash
> +++ w/contrib/completion/git-completion.bash
> @@ -348,7 +348,7 @@ __gitcomp ()
>  
>  # Clear the variables caching builtins' options when (re-)sourcing
>  # the completion script.
> -if [[ -n ${ZSH_VERSION-} ]]; then
> +if [[ -n ${ZSH_VERSION-} || -n ${GIT_SOURCING_ZSH_COMPLETION-} ]]; then
>  	unset $(set |sed -ne 's/^\(__gitcomp_builtin_[a-zA-Z0-9_][a-zA-Z0-9_]*\)=.*/\1/p') 2>/dev/null
>  else
>  	unset $(compgen -v __gitcomp_builtin_)
> diff --git i/contrib/completion/git-completion.zsh w/contrib/completion/git-completion.zsh
> index 53cb0f934f..c7be9fd4dc 100644
> --- i/contrib/completion/git-completion.zsh
> +++ w/contrib/completion/git-completion.zsh
> @@ -39,7 +39,7 @@ if [ -z "$script" ]; then
>  		test -f $e && script="$e" && break
>  	done
>  fi
> -ZSH_VERSION='' . "$script"
> +GIT_SOURCING_ZSH_COMPLETION=1 ZSH_VERSION='' . "$script"
>  
>  __gitcomp ()
>  {
> 

Being in RC phase, I'm all for aiming for a minimal solution.
However, I don't think that the better fix would be erm.. any "less
minimal":

diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index f2aa484758..7aeb575cd1 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -3244,7 +3244,10 @@ __gitk_main ()
 	__git_complete_revlist
 }
 
-if [[ -n ${ZSH_VERSION-} ]]; then
+if [[ -n ${ZSH_VERSION-} ]] &&
+   # Don't define these functions when sourced from 'git-completion.zsh',
+   # it has its own implementations.
+   [[ -z "${GIT_SOURCING_ZSH_COMPLETION}" ]] ; then
 	echo "WARNING: this script is deprecated, please see git-completion.zsh" 1>&2
 
 	autoload -U +X compinit && compinit
diff --git a/contrib/completion/git-completion.zsh b/contrib/completion/git-completion.zsh
index 53cb0f934f..049d6b80f6 100644
--- a/contrib/completion/git-completion.zsh
+++ b/contrib/completion/git-completion.zsh
@@ -39,7 +39,7 @@ if [ -z "$script" ]; then
 		test -f $e && script="$e" && break
 	done
 fi
-ZSH_VERSION='' . "$script"
+GIT_SOURCING_ZSH_COMPLETION=y . "$script"
 
 __gitcomp ()
 {