Enable Travis CI (awakesecurity#49)

* enable travis ci

* pin nixpkgs without NIXPATH

* remove nixpkgs.json

* fix type error

* fix nixpkgs hash

.travis.yml

@@ -0,0 +1,2 @@
+language: nix
+script: nix-build --attr proto3-suite-linux release.nix

README.md

@@ -1,5 +1,7 @@
 # `proto3-suite`
 
+[![Build Status](https://travis-ci.org/awakesecurity/proto3-suite.svg?branch=master)](https://travis-ci.org/awakesecurity/proto3-suite)
+
 This package defines tools for working with protocol buffers version 3 in Haskell.
 
 This library provides a higher-level API to

fetch-nixpkgs.nix

@@ -0,0 +1,51 @@
+{ rev                             # The Git revision of nixpkgs to fetch
+, sha256                          # The SHA256 of the downloaded data
+, system ? builtins.currentSystem # This is overridable if necessary
+}:
+
+with {
+  ifThenElse = { bool, thenValue, elseValue }: (
+    if bool then thenValue else elseValue);
+};
+
+ifThenElse {
+  bool = (0 <= builtins.compareVersions builtins.nixVersion "1.12");
+
+  # In Nix 1.12, we can just give a `sha256` to `builtins.fetchTarball`.
+  thenValue = (
+    builtins.fetchTarball {
+      url = "https://github.com/NixOS/nixpkgs/archive/${rev}.tar.gz";
+      inherit sha256;
+    });
+
+  # This hack should at least work for Nix 1.11
+  elseValue = (
+    (rec {
+      tarball = import <nix/fetchurl.nix> {
+        url = "https://github.com/NixOS/nixpkgs/archive/${rev}.tar.gz";
+        inherit sha256;
+      };
+
+      builtin-paths = import <nix/config.nix>;
+
+      script = builtins.toFile "nixpkgs-unpacker" ''
+        "$coreutils/mkdir" "$out"
+        cd "$out"
+        "$gzip" --decompress < "$tarball" | "$tar" -x --strip-components=1
+      '';
+
+      nixpkgs = builtins.derivation {
+        name = "nixpkgs-${builtins.substring 0 6 rev}";
+
+        builder = builtins.storePath builtin-paths.shell;
+
+        args = [ script ];
+
+        inherit tarball system;
+
+        tar       = builtins.storePath builtin-paths.tar;
+        gzip      = builtins.storePath builtin-paths.gzip;
+        coreutils = builtins.storePath builtin-paths.coreutils;
+      };
+    }).nixpkgs);
+}

release.nix

@@ -85,19 +85,10 @@ let
     allowUnfree = true;
   };
 
-  bootstrap = import <nixpkgs> { };
-
-  nixpkgs =
-    let
-      json = builtins.fromJSON (builtins.readFile ./nixpkgs.json);
-    in
-      bootstrap.fetchFromGitHub {
-        owner = "NixOS";
-
-        repo = "nixpkgs";
-
-        inherit (json) rev sha256;
-      };
+  nixpkgs = import ./fetch-nixpkgs.nix {
+    rev    = "7ae9da426924537755ce9164fd5b5f81ce16a1c3";
+    sha256 = "1zg1j2fsfj6qhh724nc8fnn3ig3rm6nd29zzhjrbjkszkjspc9pl";
+  };
 
    linuxPkgs = import nixpkgs { inherit config; system = "x86_64-linux" ; };
   darwinPkgs = import nixpkgs { inherit config; system = "x86_64-darwin"; };