nix: add binaryTarball derivation

[ju1m]

Copy (and adapt a little) the binaryTarball derivation found in nix's release.nix:
https://github.com/NixOS/nix/blob/4aee93d5ce6cf77e314e93074b9da1dcff8979e9/release.nix#L115

binaryTarball is useful for cross-compiling nix:

nix build nixpkgs.pkgsCross.armv7l-hf-multiplatform.nix.binaryTarball

Which builds a result/nix-2.1.3-armv7a-linux.tar.bz2
packing an install script which will create a nix store
and most importantly register in it the closure of the nix package
(using nix-store --load-db).

NOTE: the tarball can be quite bigger than expected (~450Mo), mainly because gcc is not stripped by default when cross-compiling.

Motivation for this change

Cross-compiling nix (eg. for ARM) and packing everything needed to install it in a tarball.

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.

---

[ju1m]

Unfortunately there is a problem with the cross-compiling: some packages have binaries for the host platform.

Packages of the tarball with host platform binaries:

$ find nix-2.1.3-armv7a-linux -type f -executable -exec file {} \; | grep x86-64, >x86-64.list
$ <x86-64.list sed -ne 's:^[^/]*/store/[^/-]*-\([^/]*\)/.*:\1:p' | sort -u
armv7a-unknown-linux-gnueabihf-binutils-2.30
armv7a-unknown-linux-gnueabihf-stage-final-gcc-debug-7.3.0
armv7a-unknown-linux-gnueabihf-stage-final-gcc-debug-7.3.0-lib
armv7a-unknown-linux-gnueabihf-stage-static-gcc-debug-7.3.0
armv7a-unknown-linux-gnueabihf-stage-static-gcc-debug-7.3.0-lib
bash-4.4-p23
bzip2-1.0.6.0.1
bzip2-1.0.6.0.1-bin
coreutils-8.29
expand-response-params
gcc-7.3.0
gcc-7.3.0-lib
glibc-2.27
glibc-2.27-bin
gmp-6.1.2
gnutar-1.30
gzip-1.9
isl-0.17.1
libmpc-1.1.0
mpfr-4.0.1
xz-5.2.4
xz-5.2.4-bin
zlib-1.2.11

Packages of the tarball with target platform binaries:

$ find nix-2.1.3-armv7a-linux -type f -executable -exec file {} \; | grep ARM, >arm.list
$ <arm.list sed -ne 's:^[^/]*/store/[^/-]*-\([^/]*\)/.*:\1:p' | sort -u 
armv7a-unknown-linux-gnueabihf-stage-final-gcc-debug-7.3.0
boehm-gc-7.6.6-armv7a-unknown-linux-gnueabihf
busybox-1.29.3-armv7a-unknown-linux-gnueabihf
bzip2-1.0.6.0.1-armv7a-unknown-linux-gnueabihf
curl-7.59.0-armv7a-unknown-linux-gnueabihf
curl-7.62.0-armv7a-unknown-linux-gnueabihf
glibc-2.27-armv7a-unknown-linux-gnueabihf
glibc-2.27-armv7a-unknown-linux-gnueabihf-bin
keyutils-1.5.10-armv7a-unknown-linux-gnueabihf-lib
libseccomp-2.3.3-armv7a-unknown-linux-gnueabihf-lib
libsodium-1.0.16-armv7a-unknown-linux-gnueabihf
libssh2-1.8.0-armv7a-unknown-linux-gnueabihf
nghttp2-1.32.0-armv7a-unknown-linux-gnueabihf-lib
nix-2.1.3-armv7a-unknown-linux-gnueabihf
openssl-1.0.2p-armv7a-unknown-linux-gnueabihf
sqlite-3.24.0-armv7a-unknown-linux-gnueabihf
xz-5.2.4-armv7a-unknown-linux-gnueabihf
zlib-1.2.11-armv7a-unknown-linux-gnueabihf

Note also that curl appears two times.

[nixos-discourse]

This pull request has been mentioned on Nix community. There might be relevant details there:

https://discourse.nixos.org/t/how-to-install-nix-package-manager-on-raspbian/2035/9

[edolstra]

IMHO this is not the right approach since:

• It duplicates code from Nix's release.nix.

• It adds a non-package derivation to Nixpkgs, so it clutters the package list (e.g. nix-binary-tarball will show up in nix-env -qa).

[matthewbauer]

Ok closing for now. Thanks for the contribution but I think there is a better way. I've opened a PR at Nix to add some binary tarballs for armv6 & armv7:

NixOS/nix#2667