Pin nixpkgs to latest nixos-19.03

Author: rvl

.buildkite/pipeline.yml

@@ -1,9 +1,5 @@
-env:
-  NIX_PATH: "nixpkgs=channel:nixos-18.09"
-  NIX_BUILD_ARGS: "--cores 0 --max-jobs 2"
-
 steps:
   - label: 'Run tests'
-    command: "NIX_PATH=nixpkgs=channel:nixos-18.09 ./test/tests.sh"
+    command: "./test/tests.sh"
     agents:
       system: x86_64-linux

.buildkite/updates.yml

@@ -1,15 +1,15 @@
 steps:
   - label: 'Update hackage.nix'
     command:
-      - nix-build -I nixpkgs=channel:nixos-18.09 -A maintainer-scripts.update-hackage -o update-hackage.sh
+      - nix-build -A maintainer-scripts.update-hackage -o update-hackage.sh
       - echo "+++ Updating hackage.nix"
       - ./update-hackage.sh
     agents:
       system: x86_64-linux
 
   - label: 'Update stackage.nix'
     command:
-      - nix-build -I nixpkgs=channel:nixos-18.09 -A maintainer-scripts.update-stackage -o update-stackage.sh
+      - nix-build -A maintainer-scripts.update-stackage -o update-stackage.sh
       - echo "+++ Updating stackage.nix"
       - ./update-stackage.sh
     agents:

default.nix

@@ -1,4 +1,6 @@
-{ pkgs ? import <nixpkgs> {}
+{ pkgs ? import nixpkgs {}
+# Use a pinned nixpkgs rather than the one on NIX_PATH
+, nixpkgs ? ./nixpkgs
 
 # You can provide different pins for hackage.nix and stackage.nix if required.
 # It's also possible to override these sources with NIX_PATH.

nixpkgs/default.nix

@@ -0,0 +1,7 @@
+let
+  fetchFromGitHub = { owner, repo, rev, sha256, ... }:
+    builtins.fetchTarball {
+      inherit sha256;
+      url = "https://github.com/${owner}/${repo}/archive/${rev}.tar.gz";
+    };
+in import (fetchFromGitHub (builtins.fromJSON (builtins.readFile ./github.json)))

nixpkgs/github.json

@@ -0,0 +1,6 @@
+{
+  "owner": "NixOS",
+  "repo": "nixpkgs",
+  "rev": "91cb80e4397d55b19b0beba3fa3846f1a02d0342",
+  "sha256": "1pm6n9xwqd5c4khcyfsygni77wwfjh4ggy502k0g4am0xm4gjjs6"
+}

test/default.nix

@@ -1,4 +1,5 @@
-{ pkgs ? import <nixpkgs> { }
+{ pkgs ? import nixpkgs {}
+, nixpkgs ? ./nixpkgs
 , haskell ? pkgs.callPackage ../. { }
 }: