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.
environment variable. This is useful for passing authentication
information (it won't show up in `ps'). Hacky - nix-push should
abstract over the use of Curl.
print a nice backtrace of the stack, rather than vomiting a gigantic
(and useless) aterm on the screen. Example:
error: while evaluating file `.../pkgs/system/test.nix':
while evaluating attribute `subversion' at `.../pkgs/system/all-packages-generic.nix', line 533:
while evaluating function at `.../pkgs/applications/version-management/subversion/default.nix', line 1:
assertion failed at `.../pkgs/applications/version-management/subversion/default.nix', line 13
Since the Nix expression language is lazy, the trace may be
misleading. The purpose is to provide a hint as to the location of
the problem.
instead of `derivation' triggered a huge slowdown in the Nix
expression evaluator. Total execution time of `nix-env -qa' went up
by a factor of 60 or so.
This scalability problem was caused by expressions such as
(x: y: ... x ...) a b
where `a' is a large term (say, the one in
`all-packages-generic.nix'). Then the first beta-reduction would
produce
(y: ... a ...) b
by substituting `a' for `x'. The second beta-reduction would then
substitute `b' for `y' into the body `... a ...', which is a large
term due to `a', and thus causes a large traversal to be performed
by substitute() in the second reduction. This is however entirely
redundant, since `a' cannot contain free variables (since we never
substitute below a weak head normal form).
The solution is to wrap substituted terms into a `Closed'
constructor, i.e.,
subst(subs, Var(x)) = Closed(e) iff subs[x] = e
have substitution not descent into closed terms,
subst(subs, Closed(x)) = Closed(x)
and otherwise ignore them for evaluation,
eval(Closed(x)) = eval(x).
* Fix a typo that caused incorrect substitutions to be performed in
simple lambdas, e.g., `(x: x: x) a' would reduce to `(x: a)'.
`bla:' is now no longer parsed as a URL.
* Re-enabled support for the `args' attribute in derivations to
specify command line arguments to the builder, e.g.,
...
builder = /usr/bin/python;
args = ["-c" ./builder.py];
...
This is because the contents of these symlinks are not incorporated
into the hashes of derivations, and could therefore cause a mismatch
between the build system and the target system. E.g., if
`/nix/store' is a symlink to `/data/nix/store', then a builder could
expand this path and store the result. If on the target system
`/nix/store' is not a symlink, or is a symlink that points somewhere
else, we have a dangling pointer.
The trigger for this change is that gcc 3.3.3 does exactly that (it
applies realpath() to some files, such as libraries, which causes
our impurity checker to bail out.)
An annoying side-effect of this change is that it makes it harder to
move the Nix store to a different file system. On Linux, bind
mounts can be used instead of symlink for this purpose (e.g., `mount
-o bind /data/nix/store /nix/store').
writes to stderr:
- `pretty': the old nested style (default)
- `escapes': uses escape codes to indicate nesting and message
level; can be processed using `log2xml'
- `flat': just plain text, no nesting
These can be set using `--log-type TYPE' or the NIX_LOG_TYPE
environment variable.
unimportant messages, it is collapsed by the default.
* Also added an optional integer argument to the escape code for opening a nesting
level to indicate lack of importance. If set, the tree is collapsed by default.
build logs. The program `log2xml' converts a Nix build log (read
from standard input) into XML file that can then be converted to
XHTML by the `log2html.xsl' stylesheet. The CSS stylesheet
`logfile.css' is necessary to make it look good.
This is primarily useful if the log file has a *tree structure*,
i.e., that sub-tasks such as the various phases of a build (unpack,
configure, make, etc.) or recursive invocations of Make are
represented as such. While a log file is in principle an
unstructured plain text file, builders can communicate this tree
structure to `log2xml' by using escape sequences:
- "\e[p" starts a new nesting level; the first line following the
escape code is the header;
- "\e[q" ends the current nesting level.
The generic builder in nixpkgs (not yet committed) uses this. It
shouldn't be to hard to patch GNU Make to speak this protocol.
Further improvements to the generated HTML pages are to allow
collapsing/expanding of subtrees, and to abbreviate store paths (but
to show the full path by hovering the mouse over it).
builders to point to the store and the temporary build directory,
respectively. Useful for purity checking.
* Also set TEMPDIR, TMPDIR, TEMP, and TEMP to NIX_BUILD_TOP to make
sure that tools in the builder store temporary files in the right
location.
