Sample zsh completion for git branches you aren't on

gistfile1.txt

#compdef test

local arguments

_branch(){
    val=()

    git branch | grep -v "\*" | while read -r branch ; do
        val=($val $branch)
    done
}

local expl
local -a val

arguments=(
'--branch[The git branch]: :->branch'
)

case "$state" in
    branch)
        _branch
        _wanted val expl "Branches" compadd -a val
        ;;  
esac

_arguments $arguments