This adds a command 'nix make-content-addressable' that rewrites the
specified store paths into content-addressable paths. The advantage of
such paths is that 1) they can be imported without signatures; 2) they
can enable deduplication in cases where derivation changes do not
cause output changes (apart from store path hashes).
For example,
$ nix make-content-addressable -r nixpkgs.cowsay
rewrote '/nix/store/g1g31ah55xdia1jdqabv1imf6mcw0nb1-glibc-2.25-49' to '/nix/store/48jfj7bg78a8n4f2nhg269rgw1936vj4-glibc-2.25-49'
...
rewrote '/nix/store/qbi6rzpk0bxjw8lw6azn2mc7ynnn455q-cowsay-3.03+dfsg1-16' to '/nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16'
We can then copy the resulting closure to another store without
signatures:
$ nix copy --trusted-public-keys '' ---to ~/my-nix /nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16
In order to support self-references in content-addressable paths,
these paths are hashed "modulo" self-references, meaning that
self-references are zeroed out during hashing. Somewhat annoyingly,
this means that the NAR hash stored in the Nix database is no longer
necessarily equal to the output of "nix hash-path"; for
content-addressable paths, you need to pass the --modulo flag:
$ nix path-info --json /nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16 | jq -r .[].narHash
sha256:0ri611gdilz2c9rsibqhsipbfs9vwcqvs811a52i2bnkhv7w9mgw
$ nix hash-path --type sha256 --base32 /nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16
1ggznh07khq0hz6id09pqws3a8q9pn03ya3c03nwck1kwq8rclzs
$ nix hash-path --type sha256 --base32 /nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16 --modulo iq6g2x4q62xp7y7493bibx0qn5w7xz67
0ri611gdilz2c9rsibqhsipbfs9vwcqvs811a52i2bnkhv7w9mgw
Experimental features are now opt-in. There is currently one
experimental feature: "nix-command" (which enables the "nix"
command. 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
(cherry picked from commit 8e478c2341,
without the "flakes" feature)
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
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.
Only variables that were marked as exported are exported in the dev
shell. Also, we no longer try to parse the function section of the env
file, fixing
$ nix dev-shell
error: shell environment '/nix/store/h7ama3kahb8lypf4nvjx34z06g9ncw4h-nixops-1.7pre20190926.4c7acbb-env' has unexpected line '/^[a-z]?"""/ {'
If 'input.<name>.uri' changes, then the entry in the lockfile for
input <name> should be considered stale.
Also print some messages when lock file entries are added/updated.
So you now get
$ nix build
error: path '.' is not a flake (because it does not reference a Git repository)
rather than
$ nix build
error: unsupported argument '.'
Instead of a list, inputs are now an attrset like
inputs = {
nixpkgs.uri = github:NixOS/nixpkgs;
};
If 'uri' is omitted, than the flake is a lookup in the flake registry, e.g.
inputs = {
nixpkgs = {};
};
but in that case, you can also just omit the input altogether and
specify it as an argument to the 'outputs' function, as in
outputs = { self, nixpkgs }: ...
This also gets rid of 'nonFlakeInputs', which are now just a special
kind of input that have a 'flake = false' attribute, e.g.
inputs = {
someRepo = {
uri = github:example/repo;
flake = false;
};
};
