fetchTarball, fetchTree, and fetchGit all have *optional* hash attrs.
This means that we need to be careful with what we allow to avoid
accidentally making these defaults. When ‘hash = ""’ we assume the
empty hash is wanted.
follow up of https://github.com/NixOS/nix/pull/3544
This allows hash="" so that it can be used for debugging purposes. For
instance, this gives you an error message like:
warning: found empty hash, assuming you wanted 'sha256:0000000000000000000000000000000000000000000000000000'
hash mismatch in fixed-output derivation '/nix/store/asx6qw1r1xk6iak6y6jph4n58h4hdmbm-nix':
wanted: sha256:0000000000000000000000000000000000000000000000000000
got: sha256:0fpfhipl9v1mfzw2ffmxiyyzqwlkvww22bh9wcy4qrfslb4jm429
This provides a pluggable mechanism for defining new fetchers. It adds
a builtin function 'fetchTree' that generalizes existing fetchers like
'fetchGit', 'fetchMercurial' and 'fetchTarball'. 'fetchTree' takes a
set of attributes, e.g.
fetchTree {
type = "git";
url = "https://example.org/repo.git";
ref = "some-branch";
rev = "abcdef...";
}
The existing fetchers are just wrappers around this. Note that the
input attributes to fetchTree are the same as flake input
specifications and flake lock file entries.
All fetchers share a common cache stored in
~/.cache/nix/fetcher-cache-v1.sqlite. This replaces the ad hoc caching
mechanisms in fetchGit and download.cc (e.g. ~/.cache/nix/{tarballs,git-revs*}).
This also adds support for Git worktrees (c169ea5904).
This allows querying the location of function arguments. E.g.
builtins.unsafeGetAttrPos "x" (builtins.functionArgs ({ x }: null))
=> { column = 57; file = "/home/infinisil/src/nix/inst/test.nix"; line = 1; }
Fixes
error: derivation '/nix/store/klivma7r7h5lndb99f7xxmlh5whyayvg-zlib-1.2.11.drv' has incorrect output '/nix/store/fv98nnx5ykgbq8sqabilkgkbc4169q05-zlib-1.2.11-dev', should be '/nix/store/adm7pilzlj3z5k249s8b4wv3scprhzi1-zlib-1.2.11-dev'
Most functions now take a StorePath argument rather than a Path (which
is just an alias for std::string). The StorePath constructor ensures
that the path is syntactically correct (i.e. it looks like
<store-dir>/<base32-hash>-<name>). Similarly, functions like
buildPaths() now take a StorePathWithOutputs, rather than abusing Path
by adding a '!<outputs>' suffix.
Note that the StorePath type is implemented in Rust. This involves
some hackery to allow Rust values to be used directly in C++, via a
helper type whose destructor calls the Rust type's drop()
function. The main issue is the dynamic nature of C++ move semantics:
after we have moved a Rust value, we should not call the drop function
on the original value. So when we move a value, we set the original
value to bitwise zero, and the destructor only calls drop() if the
value is not bitwise zero. This should be sufficient for most types.
Also lots of minor cleanups to the C++ API to make it more modern
(e.g. using std::optional and std::string_view in some places).
For text files it is possible to do it like so:
`builtins.hashString "sha256" (builtins.readFile /tmp/a)`
but that doesn't work for binary files.
With builtins.hashFile any kind of file can be conveniently hashed.
Previously, plain derivation paths in the string context (e.g. those
that arose from builtins.storePath on a drv file, not those that arose
from accessing .drvPath of a derivation) were treated somewhat like
derivaiton paths derived from .drvPath, except their dependencies
weren't recursively added to the input set. With this change, such
plain derivation paths are simply treated as paths and added to the
source inputs set accordingly, simplifying context handling code and
removing the inconsistency. If drvPath-like behavior is desired, the
.drv file can be imported and then .drvPath can be accessed.
This is a backwards-incompatibility, but storePath is never used on
drv files within nixpkgs and almost never used elsewhere.
SRI hashes (https://www.w3.org/TR/SRI/) combine the hash algorithm and
a base-64 hash. This allows more concise and standard hash
specifications. For example, instead of
import <nix/fetchurl.nl> {
url = https://nixos.org/releases/nix/nix-2.1.3/nix-2.1.3.tar.xz;
sha256 = "5d22dad058d5c800d65a115f919da22938c50dd6ba98c5e3a183172d149840a4";
};
you can write
import <nix/fetchurl.nl> {
url = https://nixos.org/releases/nix/nix-2.1.3/nix-2.1.3.tar.xz;
hash = "sha256-XSLa0FjVyADWWhFfkZ2iKTjFDda6mMXjoYMXLRSYQKQ=";
};
In fixed-output derivations, the outputHashAlgo is no longer mandatory
if outputHash specifies the hash (either as an SRI or in the old
"<type>:<hash>" format).
'nix hash-{file,path}' now print hashes in SRI format by default. I
also reverted them to use SHA-256 by default because that's what we're
using most of the time in Nixpkgs.
Suggested by @zimbatm.
forceValue() were called after a value is copied effectively forcing only one of the copies keeping another copy not evaluated.
This resulted in its evaluation of the same lazy value more than once (the number of hits is not big though)
