pin haskell.nix and iohk-nix using niv

lib.nix

@@ -1,30 +1,23 @@
 let
-  # Allow overriding pinned nixpkgs for debugging purposes via cardano_pkgs
-  # Imports the iohk-nix library.
-  # The version can be overridden for debugging purposes by setting
-  # NIX_PATH=iohk_nix=/path/to/iohk-nix
-  iohkNix = import (
-    let try = builtins.tryEval <iohk_nix>;
-    in if try.success
-    then builtins.trace "using host <iohk_nix>" try.value
-    else
-      let
-        spec = builtins.fromJSON (builtins.readFile ./nix/iohk-nix-src.json);
-      in builtins.fetchTarball {
-        url = "${spec.url}/archive/${spec.rev}.tar.gz";
-        inherit (spec) sha256;
-      }) {};
-  # Gets the value of an environment variable, with a default if it's
-  # unset or empty.
+  sources = import ./nix/sources.nix;
+  pkgs' = import sources.nixpkgs {};
+  haskellNixJson = let
+    src = sources."haskell.nix";
+  in __toJSON {
+    inherit (sources."haskell.nix") rev sha256;
+    url = "https://github.com/${src.owner}/${src.repo}";
+  };
+  iohkNix = import sources.iohk-nix { haskellNixJsonOverride = pkgs'.writeText "haskell-nix.json" haskellNixJson; };
+  pkgs = iohkNix.pkgs;
+  lib = pkgs.lib;
+  niv = (import sources.niv {}).niv;
   maybeEnv = env: default:
     let
       result = builtins.getEnv env;
     in if result != ""
        then result
        else default;
 
-  pkgs = iohkNix.pkgs;
-  lib = pkgs.lib;
   environments = iohkNix.cardanoLib.environments // {
     demo = {
         confKey = "dev";
@@ -36,7 +29,7 @@ let
     (name: env: f (env // { inherit name; }))
     environments;
 in lib // iohkNix.cardanoLib // iohkNix // {
-  inherit environments forEnvironments;
+  inherit environments forEnvironments niv iohkNix;
   utf8LocaleSetting = ''
     export LC_ALL=en_GB.UTF-8
     export LANG=en_GB.UTF-8

nix/sources.json

@@ -0,0 +1,62 @@
+{
+    "gitignore": {
+        "branch": "master",
+        "description": "Nix function for filtering local git sources",
+        "homepage": "",
+        "owner": "hercules-ci",
+        "repo": "gitignore",
+        "rev": "f9e996052b5af4032fe6150bba4a6fe4f7b9d698",
+        "sha256": "0jrh5ghisaqdd0vldbywags20m2cxpkbbk5jjjmwaw0gr8nhsafv",
+        "type": "tarball",
+        "url": "https://github.com/hercules-ci/gitignore/archive/f9e996052b5af4032fe6150bba4a6fe4f7b9d698.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "haskell.nix": {
+        "branch": "master",
+        "description": "Alternative Haskell Infrastructure for Nixpkgs",
+        "homepage": "https://input-output-hk.github.io/haskell.nix",
+        "owner": "input-output-hk",
+        "repo": "haskell.nix",
+        "rev": "3ae2303b14bdebd00437b0e995af2d0eb21abafe",
+        "sha256": "0dk6541kwfyc5sp5h1vfk6zl4ghln4i2zqkaijbjwv8bnixnm6wl",
+        "type": "tarball",
+        "url": "https://github.com/input-output-hk/haskell.nix/archive/3ae2303b14bdebd00437b0e995af2d0eb21abafe.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "iohk-nix": {
+        "branch": "master",
+        "description": "nix scripts shared across projects",
+        "homepage": null,
+        "owner": "input-output-hk",
+        "repo": "iohk-nix",
+        "rev": "f854c957a65295639d2062867552b65c7dc227a6",
+        "sha256": "1jl07ng2nx6lgj9rrqzl242r263505llzzxb592fn81h0dq6jx1r",
+        "type": "tarball",
+        "url": "https://github.com/input-output-hk/iohk-nix/archive/f854c957a65295639d2062867552b65c7dc227a6.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "niv": {
+        "branch": "iohk",
+        "description": "Easy dependency management for Nix projects",
+        "homepage": "https://github.com/nmattia/niv",
+        "owner": "input-output-hk",
+        "repo": "niv",
+        "rev": "c25268460b72cea5b7294354ab019997530a6f3d",
+        "sha256": "1fgq1nkycm54f431h6wflh6rr7xsq3q2fq9drbgra2fnrsyn65ll",
+        "type": "tarball",
+        "url": "https://github.com/input-output-hk/niv/archive/c25268460b72cea5b7294354ab019997530a6f3d.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "nixpkgs": {
+        "branch": "iohk-19.03",
+        "description": "Nix Packages collection",
+        "homepage": null,
+        "owner": "input-output-hk",
+        "repo": "nixpkgs",
+        "rev": "5bd4c4ea6804b54683ef2b802d970ae473e1b658",
+        "sha256": "12gah6y1lkkgvvdgswyzsqyvxvsvljn61vpy606sy37yfgkc1a63",
+        "type": "tarball",
+        "url": "https://github.com/input-output-hk/nixpkgs/archive/5bd4c4ea6804b54683ef2b802d970ae473e1b658.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    }
+}

nix/sources.nix

@@ -0,0 +1,130 @@
+# This file has been generated by Niv.
+
+# A record, from name to path, of the third-party packages
+with rec
+{
+  pkgs =
+    if hasNixpkgsPath
+    then
+        if hasThisAsNixpkgsPath
+        then import (builtins_fetchTarball { inherit (sources_nixpkgs) url sha256; }) {}
+        else import <nixpkgs> {}
+    else
+        import (builtins_fetchTarball { inherit (sources_nixpkgs) url sha256; }) {};
+
+  sources_nixpkgs =
+    if builtins.hasAttr "nixpkgs" sources
+    then sources.nixpkgs
+    else abort
+    ''
+        Please specify either <nixpkgs> (through -I or NIX_PATH=nixpkgs=...) or
+        add a package called "nixpkgs" to your sources.json.
+    '';
+
+  sources_gitignore =
+    if builtins.hasAttr "gitignore" sources
+    then sources.gitignore
+    else abort
+    ''
+        Please add "gitignore" to your sources.json:
+        niv add hercules-ci/gitignore
+    '';
+
+  inherit (import (builtins_fetchTarball { inherit (sources_gitignore) url sha256; }) {
+    inherit (pkgs) lib;
+  }) gitignoreSource;
+
+  # fetchTarball version that is compatible between all the versions of Nix
+  builtins_fetchTarball =
+      { url, sha256 ? null }@attrs:
+      let
+        inherit (builtins) lessThan nixVersion fetchTarball;
+      in
+        if sha256 == null || lessThan nixVersion "1.12" then
+          fetchTarball { inherit url; }
+        else
+          fetchTarball attrs;
+
+  # fetchurl version that is compatible between all the versions of Nix
+  builtins_fetchurl =
+      { url, sha256 ? null }@attrs:
+      let
+        inherit (builtins) lessThan nixVersion fetchurl;
+      in
+        if sha256 == null || lessThan nixVersion "1.12" then
+          fetchurl { inherit url; }
+        else
+          fetchurl attrs;
+
+  # A wrapper around pkgs.fetchzip that has inspectable arguments,
+  # annoyingly this means we have to specify them
+  fetchzip = { url, sha256  ? null }@attrs: if sha256 == null
+    then builtins.fetchTarball { inherit url; }
+    else pkgs.fetchzip attrs;
+
+  # A wrapper around pkgs.fetchurl that has inspectable arguments,
+  # annoyingly this means we have to specify them
+  fetchurl = { url, sha256 }@attrs: pkgs.fetchurl attrs;
+
+  hasNixpkgsPath = (builtins.tryEval <nixpkgs>).success;
+  hasThisAsNixpkgsPath =
+    (builtins.tryEval <nixpkgs>).success && <nixpkgs> == ./.;
+
+  sources = builtins.fromJSON (builtins.readFile ./sources.json);
+
+  mapAttrs = builtins.mapAttrs or
+    (f: set: with builtins;
+      listToAttrs (map (attr: { name = attr; value = f attr set.${attr}; }) (attrNames set)));
+
+  # borrowed from nixpkgs
+  functionArgs = f: f.__functionArgs or (builtins.functionArgs f);
+  callFunctionWith = autoArgs: f: args:
+    let auto = builtins.intersectAttrs (functionArgs f) autoArgs;
+    in f (auto // args);
+
+  getFetcher = spec:
+    let fetcherName =
+      if builtins.hasAttr "type" spec
+      then builtins.getAttr "type" spec
+      else "builtin-tarball";
+    in builtins.getAttr fetcherName {
+      "tarball" = fetchzip;
+      "builtin-tarball" = builtins_fetchTarball;
+      "file" = fetchurl;
+      "builtin-url" = builtins_fetchurl;
+    };
+};
+# NOTE: spec must _not_ have an "outPath" attribute
+mapAttrs (name: spec:
+  if builtins.hasAttr "outPath" spec
+  then abort
+    "The values in sources.json should not have an 'outPath' attribute"
+  else
+    let
+      host = if (name == "nixpkgs") then "custom_nixpkgs" else name;
+      tryFromPath = builtins.tryEval (builtins.findFile builtins.nixPath host);
+      defaultSpec = (if builtins.hasAttr "url" spec && builtins.hasAttr "sha256" spec
+        then spec //
+            { outPath = callFunctionWith spec (getFetcher spec) { }; }
+        else spec) // (if tryFromPath.success
+          then let path = tryFromPath.value;
+          in {
+            outPath = builtins.trace "using search host <${host}>" (
+              if pkgs.lib.hasPrefix "/nix/store" (builtins.toString path)
+              then path else gitignoreSource path);
+          }
+          else {});
+    in if builtins.hasAttr "rev" spec && builtins.hasAttr "url" spec then
+      defaultSpec //
+        { revOverride = rev: if (rev == null) then defaultSpec else
+              let
+                spec' = removeAttrs (spec // {
+                  rev = rev;
+                  url = builtins.replaceStrings [defaultSpec.rev] [rev] defaultSpec.url;
+                }) [ "sha256" ];
+              in
+                spec' //
+                { outPath = callFunctionWith spec' (getFetcher spec') { };  };
+        }
+      else defaultSpec
+  ) sources

nix/update-iohk-nix.sh

@@ -1,9 +1,3 @@
 #!/usr/bin/env nix-shell
-#!nix-shell -i bash -p nix-prefetch-git
-
-set -euo pipefail
-
-NIX_DIR=$(dirname "$0")
-
-nix-prefetch-git https://github.com/input-output-hk/iohk-nix refs/heads/haskell-nix-cardano-sl \
-                 > "$NIX_DIR/iohk-nix-src.json"
+#!nix-shell -A devops ../shell.nix -i bash
+niv update iohk-nix

shell.nix

@@ -0,0 +1,23 @@
+{ localLib ? import ./lib.nix
+}:
+let
+  pkgs = localLib.iohkNix.pkgs;
+  default = import ./default.nix {};
+  devops = pkgs.stdenv.mkDerivation {
+    name = "devops-shell";
+    buildInputs = [
+      localLib.niv
+    ];
+    shellHook = ''
+      echo "DevOps Tools" \
+      | ${pkgs.figlet}/bin/figlet -f banner -c \
+      | ${pkgs.lolcat}/bin/lolcat
+
+      echo "NOTE: you may need to export GITHUB_TOKEN if you hit rate limits with niv"
+      echo "Commands:
+        * niv update <package> - update package
+
+      "
+    '';
+  };
+in { inherit devops; }