Nix expressions in that directory are combined into an attribute set
{file1 = import file1; file2 = import file2; ...}, i.e. each Nix
expression is an attribute with the file name as the attribute
name. Also recurses into directories.
* nix-env: removed the "--import" (-I) option which set the
~/.nix-defexpr symlink.
* nix-channel: don't use "nix-env --import", instead symlink
~/.nix-defexpr/channels. So finally nix-channel --update doesn't
override any default Nix expressions but combines with them.
This means that you can have (say) a local Nixpkgs SVN tree and use
it as a default for nix-env:
$ ln -s .../path-to-nixpkgs-tree ~/.nix-defexpr/nixpkgs_svn
and be subscribed to channels (including Nixpkgs) at the same time.
(If there is any ambiguity, the -A flag can be used to
disambiguate, e.g. "nix-env -i -A nixpkgs_svn.pan".)
manifests directory. In that case, we don't do a nix-pull, so the
user gets pure source deployment.
The directory /nix/var/nix/gcroots/per-user/$USER should be
writable. (It's created automatically if
/nix/var/nix/gcroots/per-user is writable, e.g. if it has 1777
permission.)
need any info on substitutable paths, we just call the substituters
(such as download-using-manifests.pl) directly. This means that
it's no longer necessary for nix-pull to register substitutes or for
nix-channel to clear them, which makes those operations much faster
(NIX-95). Also, we don't have to worry about keeping nix-pull
manifests (in /nix/var/nix/manifests) and the database in sync with
each other.
The downside is that there is some overhead in calling an external
program to get the substitutes info. For instance, "nix-env -qas"
takes a bit longer.
Abolishing the substitutes table also makes the logic in
local-store.cc simpler, as we don't need to store info for invalid
paths. On the downside, you cannot do things like "nix-store -qR"
on a substitutable but invalid path (but nobody did that anyway).
* Never catch interrupts (the Interrupted exception).
NIX_DOWNLOAD_CACHE is set, then nix-prefetch-url will store the hash
and timestamp of downloaded files in the directory
$NIX_DOWNLOAD_CACHE. This allows it to figure out if the file is
still in the Nix store.
get the basename of the channel URL (e.g., nixpkgs-unstable). The
top-level Nix expression of the channel is now an attribute set, the
attributes of which are the individual channels (e.g.,
{nixpkgs_unstable = ...; strategoxt_unstable = ...}). This makes
attribute paths ("nix-env -qaA" and "nix-env -iA") more sensible,
e.g., "nix-env -iA nixpkgs_unstable.subversion".
a different location than the user's. This makes channels usable as
a source deployment mechanism for people who install Nix under
non-standard prefixes. (NIX-57)
Nix expressions.
To subscribe to a channel (needs to be done only once):
nix-channel --add \
http://catamaran.labs.cs.uu.nl/dist/nix/channels/nixpkgs-unstable
This just adds the given URL to ~/.nix-channels (which can also be
edited manually).
To update from all channels:
nix-channel --update
This fetches the latest expressions and pulls cache manifests. The
default Nix expression (~/.nix-defexpr) is made to point to the
conjunction of the expressions downloaded from all channels.
So to update all installed derivations in the current user
environment:
nix-channel --update
nix-env --upgrade '*'
If you are really courageous, you can put this in a cronjob or
something.
You can subscribe to multiple channels. It is not entirely clear
what happens when there are name clashes between derivations from
different channels. From nix-env/main.cc it appears that the one
with the lowest (highest?) hash will be used, which is pretty
meaningless.
