Add nix-tools

Author: rvl

default.nix

@@ -77,6 +77,12 @@ let
         modules = [ ghcHackagePatches.${compiler.nix-name} ] ++ modules;
       };
 
+    # Programs for generating Nix expressions from Cabal and Stack
+    # files.
+    nix-tools = self.callPackage ./nix-tools {
+      inherit fetchExternal;
+    };
+
     # Snapshots of Hackage and Stackage, converted to Nix expressions,
     # regularly updated.
     inherit hackage stackage;

nix-tools/default.nix

@@ -0,0 +1,15 @@
+{ symlinkJoin, fetchExternal, mkPkgSet }:
+
+let
+  src = fetchExternal {
+    name     = "nix-tools-src";
+    specJSON = ./nix-tools-src.json;
+    override = "nix-tools";
+  };
+
+  hsPkgs = import (src + "/pkgs.nix") { inherit mkPkgSet; };
+in
+  symlinkJoin {
+    name = "nix-tools";
+    paths = builtins.attrValues hsPkgs.nix-tools.components.exes;
+  }

nix-tools/nix-tools-src.json

@@ -0,0 +1,7 @@
+{
+  "url": "https://github.com/input-output-hk/nix-tools",
+  "rev": "232e4fde7f942ef234b649144016d5da0f7e2745",
+  "date": "2019-02-11T12:59:38+08:00",
+  "sha256": "1nrm9vcq443isk09z1fmlp8zxnw9p3cx95zbda29s5mky17ky2c0",
+  "fetchSubmodules": false
+}