This should make live easier for single-user (non-daemon)
installations. Note that when the daemon is used, the "calling user"
is root so we're not using any untrusted caches.
This flag causes paths that do not have a known substitute to be
quietly ignored. This is mostly useful for Charon, allowing it to
speed up deployment by letting a machine use substitutes for all
substitutable paths, instead of uploading them. The latter is
frequently faster, e.g. if the target machine has a fast Internet
connection while the source machine is on a slow ADSL line.
Binary caches can now specify a priority in their nix-cache-info file.
The binary cache substituter checks caches in order of priority. This
is to ensure that fast, static caches like nixos.org/binary-cache are
processed before slow, dynamic caches like hydra.nixos.org.
This allows disabling the use of binary caches, e.g.
$ nix-build ... --option use-binary-caches false
Note that
$ nix-build ... --option binary-caches ''
does not disable all binary caches, since the caches defined by
channels will still be used.
This operation allows fixing corrupted or accidentally deleted store
paths by redownloading them using substituters, if available.
Since the corrupted path cannot be replaced atomically, there is a
very small time window (one system call) during which neither the old
(corrupted) nor the new (repaired) contents are available. So
repairing should be used with some care on critical packages like
Glibc.
In Nixpkgs, the attribute in all-packages.nix corresponding to a
package is usually equal to the package name. However, this doesn't
work if the package contains a dash, which is fairly common. The
convention is to replace the dash with an underscore (e.g. "dbus-lib"
becomes "dbus_glib"), but that's annoying. So now dashes are valid in
variable / attribute names, allowing you to write:
dbus-glib = callPackage ../development/libraries/dbus-glib { };
and
buildInputs = [ dbus-glib ];
Since we don't have a negation or subtraction operation in Nix, this
is unambiguous.
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.
Mandatory features are features that MUST be present in a derivation's
requiredSystemFeatures attribute. One application is performance
testing, where we have a dedicated machine to run performance tests
(and nothing else). Then we would add the label "perf" to the
machine's mandatory features and to the performance testing
derivations.
"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).
Nix now requires SQLite and bzip2 to be pre-installed. SQLite is
detected using pkg-config. We required DBD::SQLite anyway, so
depending on SQLite is not a big problem.
The --with-bzip2, --with-openssl and --with-sqlite flags are gone.
environment of the given derivation in a format that can be sourced
by the shell, e.g.
$ eval "$(nix-store --print-env $(nix-instantiate /etc/nixos/nixpkgs -A pkg))"
$ NIX_BUILD_TOP=/tmp
$ source $stdenv/setup
This is especially useful to reproduce the environment used to build
a package outside of its builder for development purposes.
TODO: add a nix-build option to do the above and fetch the
dependencies of the derivation as well.
