.zshrc

# git commands which will be masked for brevity inside git repos
git_cmds=(amend branch checkout commit diff grep log ls-files reflog remote reset stat status)

# create functions for each git command that fall back to the nongit command outside of repos
function $git_cmds () {
  if git rev-parse --git-dir &>/dev/null; then
    git $0 "$@"
  else
    command $0 "$@"
  fi
}

# define completion functions for all these custom commands
function _my_${^git_cmds} () {
  local cmd="${0#_my_}"
  if git rev-parse --git-dir &>/dev/null; then
    local service="git-$cmd"
    _git "$@"
  else
    local service="$cmd"
    _normal
  fi
}

# tell zsh to use the above completion functions for the special masked git commands
for cmd in $git_cmds; do
  compdef _my_$cmd $cmd
done