Experimental features are now opt-in. There are currently two
experimental features: "nix-command" (which enables the "nix"
command), and "flakes" (which enables support for flakes). This will
allow us to merge experimental features more quickly, without
committing to supporting them indefinitely.
Typical usage:
$ nix build --experimental-features 'nix-command flakes' nixpkgs#hello
In particular, when building a flake lock file, inputs like 'nixpkgs'
are now downloaded only once. Previously, it would fetch
https://api.github.com/repos/<owner>/<repo>/tarball/<ref> and then
later https://api.github.com/repos/<owner>/<repo>/tarball/<rev>, even
though they produce the same result.
Git and GitHub now also share a cache that maps revs to a store path
and other info.
A command like
$ nix run nixpkgs#hello
will now build the attribute 'packages.${system}.hello' rather than
'packages.hello'. Note that this does mean that the flake needs to
export an attribute for every system type it supports, and you can't
build on unsupported systems. So 'packages' typically looks like this:
packages = nixpkgs.lib.genAttrs ["x86_64-linux" "i686-linux"] (system: {
hello = ...;
});
The 'checks', 'defaultPackage', 'devShell', 'apps' and 'defaultApp'
outputs similarly are now attrsets that map system types to
derivations/apps. 'nix flake check' checks that the derivations for
all platforms evaluate correctly, but only builds the derivations in
'checks.${system}'.
Fixes#2861. (That issue also talks about access to ~/.config/nixpkgs
and --arg, but I think it's reasonable to say that flakes shouldn't
support those.)
The alternative to attribute selection is to pass the system type as
an argument to the flake's 'outputs' function, e.g. 'outputs = { self,
nixpkgs, system }: ...'. However, that approach would be at odds with
hermetic evaluation and make it impossible to enumerate the packages
provided by a flake.
We're calling `wait4path` on the full, resolved `@bindir@/nix-daemon` path.
That means we're hardcoding something like:
/bin/wait4path /nix/store/zs9c5xhp3zv9p23qnjxp87nl5injsi1i-nix-2.3/bin/nix-daemon && /nix/var/nix/profiles/default/bin/nix-daemon
That seems unnecessarily fragile.
It might be better to wait4path on the path we intend to call.
Previously, SANDBOX_SHELL was set to empty when unavailable. This
caused issues when actually generating the sandbox. Instead, just set
SANDBOX_SHELL when --with-sandbox-shell= is non-empty. Alternative
implementation to https://github.com/NixOS/nix/pull/3038.
Pure mode should not try to source the user’s bashrc file. These may
have many impurities that the user does not expect to get into their
shell.
Fixes#3090
In the multi-user install script, we originally made sure no previous
references to Nix existed. This prevented any previous installs from
contaminating the new install. However, some users need the ability to
repair their existing Nix installation without uninstalling all
references to Nix. This change allows users with existing Nix
installations to use the installer, while still outputing a warning
message on the dangers of this. As a result, the multi-user install
script work much more like the single-user install script has worked
in the past.
This is a requirement for macOS Catalina users now that
/Library/LaunchDaemons/org.nixos.nix-daemon.plisg is not managed by
the Nix store. If there is ever a change to the .plist, all users will
need to rerun this install script to get the new changes. Otherwise,
changes to the launch daemon will require manual interventions.
On Catalina, the /nix filesystem might not be mounted at start time.
To avoid this service not starting, we need to keep the launch agent
outside of the Nix store. A wait4pid will hold for our /nix dir to be
mounted.
Fixes#3125.
Steven Shaw
