set -o posix

fn() { foo=abc : ; typeset +x foo; printenv|grep ^foo=; }

fn
unset -v foo
unset -f fn

func1() {
  var=1
  var=2 :       # or 'var=2 return', or another special builtin
  unset -v var
  echo $FUNCNAME: var = $var
}
func2() {
  func1
  unset -v var  # bug: fails silently
}
func1
echo ${var+"BUG: still set 1"}

unset var
func2
echo ${var+"BUG: still set 2"}

unset -v var
unset -f func1 func2

fn() { foo=abc : ; typeset +x foo; echo -n 'inside: ' ; declare -p foo; }
fn
echo outside:
declare -p foo

unset -v foo
unset -f fn

func()
{
	var=value declare -x var
	echo -n 'inside: ' ; declare -p var
}

var=one
func
echo -n 'outside: ' ; declare -p var

unset -v var
unset -f func

func()
{
	local var=local
	var=global :
	echo -n 'inside: ' ; declare -p var
}

var=outside
func
echo -n 'outside: ' ; declare -p var

unset -v var
unset -f func