This allows adding attributes like
attr = if stdenv.system == "bla" then something else null;
without changing the resulting derivation on non-<bla> platforms.
We once considered adding a special "ignore" value for this purpose,
but using null seems more elegant.
The integer constant ‘langVersion’ denotes the current language
version. It gets increased every time a language feature is
added/changed/removed. It's currently 1.
The string constant ‘nixVersion’ contains the current Nix version,
e.g. "1.2pre2980_9de6bc5".
If a derivation has multiple outputs, then we only want to download
those outputs that are actuallty needed. So if we do "nix-build -A
openssl.man", then only the "man" output should be downloaded.
Likewise if another package depends on ${openssl.man}.
The tricky part is that different derivations can depend on different
outputs of a given derivation, so we may need to restart the
corresponding derivation goal if that happens.
For example, given a derivation with outputs "out", "man" and "bin":
$ nix-build -A pkg
produces ./result pointing to the "out" output;
$ nix-build -A pkg.man
produces ./result-man pointing to the "man" output;
$ nix-build -A pkg.all
produces ./result, ./result-man and ./result-bin;
$ nix-build -A pkg.all -A pkg2
produces ./result, ./result-man, ./result-bin and ./result-2.
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.
This reverts commit 2980d1fba9. It
causes a regression in NixOS evaluation:
string `/nix/store/ya3s5gmj3b28170fpbjhgsk8wzymkpa1-pommed-1.39/etc/pommed.conf' cannot refer to other paths
vfork() is just too weird. For instance, in this build:
http://hydra.nixos.org/build/3330487
the value fromHook.writeSide becomes corrupted in the parent, even
though the child only reads from it. At -O0 the problem goes away.
Probably the child is overriding some spilled temporary variable.
If I get bored I may implement using posix_spawn() instead.
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.
If ‘--link’ is given, nix-push will create hard links to the NAR files
in the store, rather than copying them. This is faster and requires
less disk space. However, it doesn't work if the store is on a
different file system.
