This is primarily a bug fix release. It also has a number of new features: nix-prefetch-url can now download URLs specified in a Nix expression. For example, $ nix-prefetch-url -A hello.src will prefetch the file specified by the fetchurl call in the attribute hello.src from the Nix expression in the current directory, and print the cryptographic hash of the resulting file on stdout. This differs from nix-build -A hello.src in that it doesn't verify the hash, and is thus useful when you’re updating a Nix expression. You can also prefetch the result of functions that unpack a tarball, such as fetchFromGitHub. For example: $ nix-prefetch-url --unpack https://github.com/NixOS/patchelf/archive/0.8.tar.gz or from a Nix expression: $ nix-prefetch-url -A nix-repl.src The builtin function <nix/fetchurl.nix> now supports downloading and unpacking NARs. This removes the need to have multiple downloads in the Nixpkgs stdenv bootstrap process (like a separate busybox binary for Linux, or curl/mkdir/sh/bzip2 for Darwin). Now all those files can be combined into a single NAR, optionally compressed using xz. Nix now supports SHA-512 hashes for verifying fixed-output derivations, and in builtins.hashString. The new flag --option build-repeat N will cause every build to be executed N+1 times. If the build output differs between any round, the build is rejected, and the output paths are not registered as valid. This is primarily useful to verify build determinism. (We already had a --check option to repeat a previously succeeded build. However, with --check, non-deterministic builds are registered in the DB. Preventing that is useful for Hydra to ensure that non-deterministic builds don't end up getting published to the binary cache.) The options --check and --option build-repeat N, if they detect a difference between two runs of the same derivation and -K is given, will make the output of the other run available under store-path-check. This makes it easier to investigate the non-determinism using tools like diffoscope, e.g., $ nix-build pkgs/stdenv/linux -A stage1.pkgs.zlib --check -K error: derivation ‘/nix/store/l54i8wlw2265…-zlib-1.2.8.drv’ may not be deterministic: output ‘/nix/store/11a27shh6n2i…-zlib-1.2.8’ differs from ‘/nix/store/11a27shh6n2i…-zlib-1.2.8-check’ $ diffoscope /nix/store/11a27shh6n2i…-zlib-1.2.8 /nix/store/11a27shh6n2i…-zlib-1.2.8-check … ├── lib/libz.a │ ├── metadata │ │ @@ -1,15 +1,15 @@ │ │ -rw-r--r-- 30001/30000 3096 Jan 12 15:20 2016 adler32.o … │ │ +rw-r--r-- 30001/30000 3096 Jan 12 15:28 2016 adler32.o … Improved FreeBSD support. nix-env -qa --xml --meta now prints license information. The maximum number of parallel TCP connections that the binary cache substituter will use has been decreased from 150 to 25. This should prevent upsetting some broken NAT routers, and also improves performance. The Nix language now supports floating point numbers. They are based on regular C++ float and compatible with existing integers and number-related operations. Export and import to and from JSON and XML works, too. All "chroot"-containing strings got renamed to "sandbox". In particular, some Nix options got renamed, but the old names are still accepted as lower-priority aliases. This release has contributions from Anders Claesson, Anthony Cowley, Bjørn Forsman, Brian McKenna, Danny Wilson, davidak, Eelco Dolstra, Fabian Schmitthenner, FrankHB, Ilya Novoselov, janus, Jim Garrison, John Ericson, Jude Taylor, Ludovic Courtès, Manuel Jacob, Mathnerd314, Pascal Wittmann, Peter Simons, Philip Potter, Preston Bennes, Rommel M. Martinez, Sander van der Burg, Shea Levy, Tim Cuthbertson, Tuomas Tynkkynen, Utku Demir and Vladimír Čunát.