depends glib2 &&

optional_depends gtk+2 \
                 "--enable-gtk2" \
                 "--disable-gtk2" \
                 "for GTK+ 2 support" &&
optional_depends gtk+3 \
                 "--enable-gtk3" \
                 "--disable-gtk3" \
                 "for GTK+ 3 support" &&
if ! is_depends_enabled $SPELL gtk+2; then
  depends gtk+3 "--enable-gtk3"
fi