pin a nixpkgs

nix/default.nix

@@ -0,0 +1,34 @@
+let
+  hostpkgs = import <nixpkgs> {};
+
+  srcDef = builtins.fromJSON (builtins.readFile ./nixpkgs.json);
+
+  inherit (hostpkgs) fetchFromGitHub fetchpatch fetchurl;
+in import (hostpkgs.stdenv.mkDerivation {
+  name = "ofborg-nixpkgs-${builtins.substring 0 10 srcDef.rev}";
+  phases = [ "unpackPhase" "patchPhase" "moveToOut" ];
+
+  src = fetchFromGitHub {
+    owner = "NixOS";
+    repo = "nixpkgs-channels";
+    inherit (srcDef) rev sha256;
+  };
+
+  patches = [
+    (fetchurl {
+      # As of 2017-22-29 21:30:00 EST:
+      # The URL is https://github.com/NixOS/nixpkgs/pull/31150 but
+      # with master merged in so it applies cleanly.
+      url = "https://github.com/NixOS/nixpkgs/compare/master...grahamc:P-E-Meunier-mkRustCrate-rebased.patch";
+      name = "mkRustCrate-rebased.patch";
+      sha256 = "0pnk31zwr0djlxd4wifx3sdwsv87hgfd6h8agr5wzifhlqzj48cp";
+    })
+
+  ];
+
+  moveToOut = ''
+    root=$(pwd)
+    cd ..
+    mv "$root" $out
+  '';
+})

nix/nixpkgs.json

@@ -0,0 +1,7 @@
+{
+  "url": "https://github.com/nixos/nixpkgs-channels.git",
+  "rev": "2e55aec9d790cd744074fe56651f094a09695f66",
+  "date": "2017-11-28T16:52:08+00:00",
+  "sha256": "0cnabkhvx6k39g8wq4fwpg82fq3sfwy81dlk3np1zbdhp46zx96c",
+  "fetchSubmodules": true
+}

nix/update-nixpkgs.sh

@@ -0,0 +1,4 @@
+#!/bin/sh
+
+nix-prefetch-git https://github.com/nixos/nixpkgs-channels.git \
+                 --rev refs/heads/nixpkgs-unstable > ./nix/nixpkgs.json