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.
To determine which seccomp filters to install, we were incorrectly
using settings.thisSystem, which doesn't denote the actual system when
--system is used.
Fixes#2791.
Thus
$ nix dev-shell
will now build the 'provides.devShell' attribute from the flake in the
current directory. If it doesn't exist, it falls back to
'provides.defaultPackage'.
'nix dev-shell' is intended to replace nix-shell. It supports flakes,
e.g.
$ nix dev-shell nixpkgs:hello
starts a bash shell providing an environment for building 'hello'.
Like Lorri (and unlike nix-shell), it computes the build environment
by building a modified top-level derivation that writes the
environment after running $stdenv/setup to $out and exits. This
provides some caching, so it's faster than nix-shell in some cases
(especially for packages with lots of dependencies, where the setup
script takes a long time).
There also is a command 'nix print-dev-env' that prints out shell code
for setting up the build environment in an existing shell, e.g.
$ . <(nix print-dev-env nixpkgs:hello)
https://github.com/tweag/nix/issues/21
Example:
$ nix flake info dwarffs
ID: dwarffs
URI: github:edolstra/dwarffs/a83d182fe3fe528ed6366a5cec3458bcb1a5f6e1
Description: A filesystem that fetches DWARF debug info from the Internet on demand
Revision: a83d182fe3fe528ed6366a5cec3458bcb1a5f6e1
Path: /nix/store/grgd14kxxk8q4n503j87mpz48gcqpqw7-source
This ensures that the lock file is updated *before* evaluating it, and
that it gets updated for any nix command, not just 'nix build'.
Also, while computing the lock file, allow arbitrary registry lookups,
not just at top-level.
Also, improve some error messages slightly.
