#
# Restarts the shell if and only if it can restart without error.
#

emulate -LR zsh
{
  # Some users export $ZDOTDIR, which can mess things up.
  local zdotdir=$ZDOTDIR
  unset ZDOTDIR
  
  print 'Validating...'
  
  # Try if the shell can start up without errors. Passing an empty command 
  # ensures that the subshell exits immediately after executing all dotfiles.
  # We suppress standard out, since we're interested in standard error only.
  setopt multios
  local err="$(zsh --interactive --monitor --zle -c '' 2>&1 > /dev/null)"
  local -i ret=$?
  
  if (( ret )) || [[ -n $err ]]; then
    [[ -n $err ]] &&
        print -ru2 -- "$err"
    print -nu2 'Validation failed'
    (( ret )) &&
        print -nu2 " with exit status $ret"
    [[ -n $err ]] &&
        print -nu2 '. Please fix the error(s) above'
    print -u2 '.'
    print -u2 'Restart aborted.'
    
    (( ret )) ||
        (( ret = 64 ))  # EX_DATAERR; see `man 3 sysexits`.
        
    return ret
    
  else
    print 'Restarting...'
    exec zsh
  fi
} always {
  ZDOTDIR=$zdotdir
}