Their names are not perfect, so let's keep them as internal functions,
until we figure out how/if we want to expose this.
This reverts 0445126c2 (Undunder __fish_is_nth_token, 2021-06-29) (but I
did it without "git revert").
Closes#8008
The previous behavior vs the current (hopefully ideal) behavior:
* zpool attach [lists pools and devices - should list only pools]
* zpool attach tank [lists pools and devices - should list only devices already
part of pool "tank"]
* zpool attach tank da1 [lists pools and devices - should list only devices not
already part of pool "tank" or any pool, depending on -f flag to attach]
As of FreeBSD 13 (released April 2021), FreeBSD has rebased its zfs support on
top of the OpenZFS distribution previously used only/chiefly by Linux;
accordingly, it has gained support for some previously Linux-only completions.
This patch changes some completions previously predicated on a Linux ZFS
installation to the presence of an OpenZFS installation. Note that there
continue to be (and probably always will be) separate Linux-only and
FreeBSD-only completions (and not just when it comes to interacting with the
device subsystem, etc).
The local-exported variable will have disappeared by the time the
function is called.
"-V"/"--inherit-variable" is meant for something like this.
Fixes#7011
