unpack-channel.nix fails if the tarball contains a directory named the
same as the channel:
mv: cannot move 'nixpkgs' to a subdirectory of itself, '.../nixpkgs'
This commit fixes that by not moving the directory if it already has the
correct name.
This doesn't work anymore if the "strict" chroot mode is
enabled. Instead, add Nix's store path as a dependency. This ensures
that its closure is present in the chroot.
Channels can now advertise a binary cache by creating a file
<channel-url>/binary-cache-url. The channel unpacker puts these in
its "binary-caches" subdirectory. Thus, the URLS of the binary caches
for the channels added by root appear in
/nix/var/nix/profiles/per-user/eelco/channels/binary-caches/*. The
binary cache substituter reads these and adds them to the list of
binary caches.
"nix-channel --add" now accepts a second argument: the channel name.
This allows channels to have a nicer name than (say) nixpkgs_unstable.
If no name is given, it defaults to the last component of the URL
(with "-unstable" or "-stable" removed).
Also, channels are now stored in a profile
(/nix/var/nix/profiles/per-user/$USER/channels). One advantage of
this is that it allows rollbacks (e.g. if "nix-channel --update" gives
an undesirable update).
Eelco Dolstra