using the build hook mechanism, by setting the derivation attribute
"preferLocalBuild" to true. This has a few use cases:
- The user environment builder. Since it just creates a bunch of
symlinks without much computation, there is no reason to do it
remotely. In fact, doing it remotely requires the entire closure
of the user environment to be copied to the remote machine, which
is extremely wasteful.
- `fetchurl'. Performing the download on a remote machine and then
copying it to the local machine involves twice as much network
traffic as performing the download locally, and doesn't save any
CPU cycles on the local machine.
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".)
;-)
* Channels: fix channels that are plain lists of derivations (like
strategoxt-unstable) instead of functions (like nixpkgs-unstable).
This fixes the error message "error: the left-hand side of the
function call is neither a function nor a primop (built-in
operation) but a list".
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".
user environment collission between two packages due to overlapping
file names, then a package with a higher priority will overwrite the
symlinks of a package with a lower priority. E.g.,
$ nix-env --set-flag priority 5 gcc
$ nix-env --set-flag priority 10 binutils
gives gcc a higher priority than binutils (higher number = lower
priority).
allow switching between them (NIX-80).
Example: two versions of Pan:
$ nix-env -q pan
pan-0.128
pan-0.14.2.91
$ readlink $(which pan)
/nix/store/l38jrbilw269drpjkx7kinhrxj6fjh59-pan-0.14.2.91/bin/pan
At most one of them can be active any given time. Assuming than
0.14.2.91 is active, you can active 0.128 as follows:
$ nix-env --set-flag active false pan-0.14.2.91
$ nix-env --set-flag active true pan-0.128
$ readlink $(which pan)
/nix/store/nziqwnlzy7xl385kglxhg75pfl5i936n-pan-0.128/bin/pan
More flags to follow.
derivations. This is mostly to simplify the implementation of
nix-prefetch-{url, svn}, which now work properly in setuid
installations.
* Enforce valid store names in `nix-store --add / --add-fixed'.
* Formalise the notion of fixed-output derivations, i.e., derivations
for which a cryptographic hash of the output is known in advance.
Changes to such derivations should not propagate upwards through the
dependency graph. Previously this was done by specifying the hash
component of the output path through the `id' attribute, but this is
insecure since you can lie about it (i.e., you can specify any hash
and then produce a completely different output). Now the
responsibility for checking the output is moved from the builder to
Nix itself.
A fixed-output derivation can be created by specifying the
`outputHash' and `outputHashAlgo' attributes, the latter taking
values `md5', `sha1', and `sha256', and the former specifying the
actual hash in hexadecimal or in base-32 (auto-detected by looking
at the length of the attribute value). MD5 is included for
compatibility but should be considered deprecated.
* Removed the `drvPath' pseudo-attribute in derivation results. It's
no longer necessary.
* Cleaned up the support for multiple output paths in derivation store
expressions. Each output now has a unique identifier (e.g., `out',
`devel', `docs'). Previously there was no way to tell output paths
apart at the store expression level.
* `nix-hash' now has a flag `--base32' to specify that the hash should
be printed in base-32 notation.
* `fetchurl' accepts parameters `sha256' and `sha1' in addition to
`md5'.
* `nix-prefetch-url' now prints out a SHA-1 hash in base-32. (TODO: a
flag to specify the hash.)
substitute mechanism) creates a store path by downloading full NAR
archives and/or patches specified in the available manifests.
Any combination of present paths, full downloads, and patches can be
used to construct the target path. In particular, patches can be
chained in sequence; and full NAR archives of the target path can be
omitted (i.e., patch-only deployment is possible). A shortest path
algorithm is used to find the smallest set of files to be downloaded
(the edge weights are currently file sizes, but one can imagine
taking the network speed to the various source into account).
Patches are binary deltas between two store paths. To be precise,
they are the output of the `bsdiff' program applied to the NAR
archives obtained by dumping (`nix-store --dump') the two store
paths. The advantage of diff'ing NAR archives (and not, say, doing
file-by-file diffs) is that file renames/moves are handled
automatically. The disadvantage is that we cannot optimise creation
of unchanged files (by hard-linking).
The expression `with E1; E2' evaluates to E2 with all bindings in
the attribute set E1 substituted. E.g.,
with {x = 123;}; x
evaluates to 123. That is, the attribute set E1 is in scope in E2.
This is particularly useful when importing files containing lots
definitions. E.g., instead of
let {
inherit (import ./foo.nix) a b c d e f;
body = ... a ... f ...;
}
we can now say
with import ./foo.nix;
... a ... f ...
I.e., we don't have to say what variables should be brought into scope.
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.
