feat(build): Introduce build configuration using Nix

Rather than migrating to Bazel, it seems more appropriate to use Nix
for this project.

The project is split into several different components (for data
dependencies and binaries). A derivation for building an image for
Nixery itself will be added.

tools/nixery/default.nix

@@ -0,0 +1,43 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+with pkgs;
+
+rec {
+  # Go implementation of the Nixery server which implements the
+  # container registry interface.
+  #
+  # Users will usually not want to use this directly, instead see the
+  # 'nixery' derivation below, which automatically includes runtime
+  # data dependencies.
+  nixery-server = buildGoPackage {
+    name = "nixery-server";
+
+    # Technically people should not be building Nixery through 'go get'
+    # or similar (as other required files will not be included), but
+    # buildGoPackage requires a package path.
+    goPackagePath = "github.com/google/nixery";
+
+    goDeps = ./go-deps.nix;
+    src    = ./.;
+
+    meta = {
+      description = "Container image build serving Nix-backed images";
+      homepage    = "https://github.com/google/nixery";
+      license     = lib.licenses.ascl20;
+      maintainers = [ lib.maintainers.tazjin ];
+    };
+  };
+
+  # Nix expression (unimported!) which is used by Nixery to build
+  # container images.
+  nixery-builder = runCommand "build-registry-image.nix" {} ''
+    cat ${./build-registry-image.nix} > $out
+  '';
+
+  # Static files to serve on the Nixery index. This is used primarily
+  # for the demo instance running at nixery.appspot.com and provides
+  # some background information for what Nixery is.
+  nixery-static = runCommand "nixery-static" {} ''
+    cp -r ${./static} $out
+  '';
+}

tools/nixery/go-deps.nix

@@ -0,0 +1,111 @@
+# This file was generated by https://github.com/kamilchm/go2nix v1.3.0
+[
+  {
+    goPackagePath = "cloud.google.com/go";
+    fetch = {
+      type = "git";
+      url = "https://code.googlesource.com/gocloud";
+      rev = "edd0968ab5054ee810843a77774d81069989494b";
+      sha256 = "1mh8i72h6a1z9lp4cy9bwa2j87bm905zcsvmqwskdqi8z58cif4a";
+    };
+  }
+  {
+    goPackagePath = "github.com/golang/protobuf";
+    fetch = {
+      type = "git";
+      url = "https://github.com/golang/protobuf";
+      rev = "6c65a5562fc06764971b7c5d05c76c75e84bdbf7";
+      sha256 = "1k1wb4zr0qbwgpvz9q5ws9zhlal8hq7dmq62pwxxriksayl6hzym";
+    };
+  }
+  {
+    goPackagePath = "github.com/googleapis/gax-go";
+    fetch = {
+      type = "git";
+      url = "https://github.com/googleapis/gax-go";
+      rev = "bd5b16380fd03dc758d11cef74ba2e3bc8b0e8c2";
+      sha256 = "1lxawwngv6miaqd25s3ba0didfzylbwisd2nz7r4gmbmin6jsjrx";
+    };
+  }
+  {
+    goPackagePath = "github.com/hashicorp/golang-lru";
+    fetch = {
+      type = "git";
+      url = "https://github.com/hashicorp/golang-lru";
+      rev = "59383c442f7d7b190497e9bb8fc17a48d06cd03f";
+      sha256 = "0yzwl592aa32vfy73pl7wdc21855w17zssrp85ckw2nisky8rg9c";
+    };
+  }
+  {
+    goPackagePath = "go.opencensus.io";
+    fetch = {
+      type = "git";
+      url = "https://github.com/census-instrumentation/opencensus-go";
+      rev = "b4a14686f0a98096416fe1b4cb848e384fb2b22b";
+      sha256 = "1aidyp301v5ngwsnnc8v1s09vvbsnch1jc4vd615f7qv77r9s7dn";
+    };
+  }
+  {
+    goPackagePath = "golang.org/x/net";
+    fetch = {
+      type = "git";
+      url = "https://go.googlesource.com/net";
+      rev = "da137c7871d730100384dbcf36e6f8fa493aef5b";
+      sha256 = "1qsiyr3irmb6ii06hivm9p2c7wqyxczms1a9v1ss5698yjr3fg47";
+    };
+  }
+  {
+    goPackagePath = "golang.org/x/oauth2";
+    fetch = {
+      type = "git";
+      url = "https://go.googlesource.com/oauth2";
+      rev = "0f29369cfe4552d0e4bcddc57cc75f4d7e672a33";
+      sha256 = "06jwpvx0x2gjn2y959drbcir5kd7vg87k0r1216abk6rrdzzrzi2";
+    };
+  }
+  {
+    goPackagePath = "golang.org/x/sys";
+    fetch = {
+      type = "git";
+      url = "https://go.googlesource.com/sys";
+      rev = "fae7ac547cb717d141c433a2a173315e216b64c4";
+      sha256 = "11pl0dycm5d8ar7g1l1w5q2cx0lms8i15n8mxhilhkdd2xpmh8f0";
+    };
+  }
+  {
+    goPackagePath = "golang.org/x/text";
+    fetch = {
+      type = "git";
+      url = "https://go.googlesource.com/text";
+      rev = "342b2e1fbaa52c93f31447ad2c6abc048c63e475";
+      sha256 = "0flv9idw0jm5nm8lx25xqanbkqgfiym6619w575p7nrdh0riqwqh";
+    };
+  }
+  {
+    goPackagePath = "google.golang.org/api";
+    fetch = {
+      type = "git";
+      url = "https://code.googlesource.com/google-api-go-client";
+      rev = "069bea57b1be6ad0671a49ea7a1128025a22b73f";
+      sha256 = "19q2b610lkf3z3y9hn6rf11dd78xr9q4340mdyri7kbijlj2r44q";
+    };
+  }
+  {
+    goPackagePath = "google.golang.org/genproto";
+    fetch = {
+      type = "git";
+      url = "https://github.com/google/go-genproto";
+      rev = "c506a9f9061087022822e8da603a52fc387115a8";
+      sha256 = "03hh80aqi58dqi5ykj4shk3chwkzrgq2f3k6qs5qhgvmcy79y2py";
+    };
+  }
+  {
+    goPackagePath = "google.golang.org/grpc";
+    fetch = {
+      type = "git";
+      url = "https://github.com/grpc/grpc-go";
+      rev = "977142214c45640483838b8672a43c46f89f90cb";
+      sha256 = "05wig23l2sil3bfdv19gq62sya7hsabqj9l8pzr1sm57qsvj218d";
+    };
+  }
+]