Deprecation nix-eval-jobs
exposes the binary cache information now also in --check-cache-status, which
allows to build a similar feature.
nix-fast-build uses nix-eval-jobs and exposes the --skip-cached flag to replace nix-build-uncached.
Otherwise NixOS/nix#3946 might track information about possible features in nix itself.
nix-build by default will download already built packages, resulting in
unnecessary downloads even if no package has been changed.
nix-build-uncached will only build packages not yet in binary caches.
nix-build-uncached is available in nixpkgs.
For nix versions bigger than 2.3.x you need to enable at least
experimental-features = nix-command in your /etc/nix/nix.conf or
$HOME/.config/nix/nix.conf or pass -build-flags "--experimental-features nix-command"
to nix-build-uncached.
In the following example ci.nix contains all expressions
that should be built. Since only hello-nur is not yet in
the binary cache, all other packages are skipped.
[joerg@turingmachine] nix-build-uncached ci.nix
$ nix-build --dry-run ci.nix --keep-going
these derivations will be built:
/nix/store/s5alllpjx9fmdj26mf9cmxzs3xyxjn7f-hello-2.00.tar.gz.drv
/nix/store/03m2lwg4zia58zqm7hqlb3r0cgfq53cn-hello-2.00.drv
these paths will be fetched (198.28 MiB download, 681.37 MiB unpacked):
/nix/store/0mijq2b50xmgk6akxdrg3x8x0k7784jb-python3.8-kiwisolver-1.2.0
/nix/store/0q1g21q160w2cj2745r24pfn2yb8pmda-python3.8-jupyter_client-6.1.5
/nix/store/0qxi1gzv1xgpxy58nfk9pxlfqybv1198-cntr-1.2.0
# ...
$ nix build --keep-going /nix/store/s5alllpjx9fmdj26mf9cmxzs3xyxjn7f-hello-2.00.tar.gz.drv /nix/store/03m2lwg4zia58zqm7hqlb3r0cgfq53cn-hello-2.00.drv
[1/2 built, 1 copied (0.7 MiB)] connecting to 'ssh://[email protected]'
We can pass all arguments that also nix-build accept:
[joerg@turingmachine] nix-build-uncached -E 'with import <nixpkgs> {}; hello'
$ nix-build --dry-run -E with import <nixpkgs> {}; hello --keep-going
these paths will be fetched (0.04 MiB download, 0.20 MiB unpacked):
/nix/store/aldyr0pjzqydf1vn9lzz7p5gvc141fhn-hello-2.10
However this only affects the evaluation during the dry build, if you want to
pass arguments to the final nix build instead, use -build-flags:
[joerg@turingmachine] nix-build-uncached -build-flags '--builders ""' ci.nix
$ nix-build --dry-run ci.nix --builders
these derivations will be built:
/nix/store/s5alllpjx9fmdj26mf9cmxzs3xyxjn7f-hello-2.00.tar.gz.drv
/nix/store/03m2lwg4zia58zqm7hqlb3r0cgfq53cn-hello-2.00.drv
these paths will be fetched (198.28 MiB download, 681.37 MiB unpacked):
/nix/store/0mijq2b50xmgk6akxdrg3x8x0k7784jb-python3.8-kiwisolver-1.2.0
/nix/store/0q1g21q160w2cj2745r24pfn2yb8pmda-python3.8-jupyter_client-6.1.5
/nix/store/0qxi1gzv1xgpxy58nfk9pxlfqybv1198-cntr-1.2.0
# ...
$ nix build --builders /nix/store/s5alllpjx9fmdj26mf9cmxzs3xyxjn7f-hello-2.00.tar.gz.drv /nix/store/03m2lwg4zia58zqm7hqlb3r0cgfq53cn-hello-2.00.drv
[1/2 built, 1 copied (0.7 MiB)] connecting to 'ssh://[email protected]'
We cannot support flakes directly at the time because nix-build does
not accept those and nix build's --no-dry-run is broken.
However it is possible to add a wrapper nix expression that imports a flake.
The following example imports hydra jobs from a nix flake the same directory.
It assumes that the flake also has nixpkgs in its inputs.
let
outputs = builtins.getFlake (toString ./.);
pkgs = outputs.inputs.nixpkgs;
drvs = pkgs.lib.collect pkgs.lib.isDerivation outputs.hydraJobs;
in drvs$ nix-build-uncached ./ci.nixIf your package set you are building has packages at the top level scope that
have the attribute allowSubstitutes = false; set, than nix-build-uncached
will build/download them everytime. This attribute is set for some builders such
as writeText or writeScriptBin. A workaround is to use the following
nix library and save it as
force_cached.nix. Than wrap your attribute set like this:
let
pkgs = import <nixpkgs> {};
in (pkgs.callPackage ./force_cached.nix {}) {
hello = pkgs.writeScriptBin "hello" ''
#!/bin/sh
exec ${pkgs.hello}/bin/hello
'';
}