Use shell.nix from hydra-poc

The shellFor function used before seem to try to do too much, and set
up some specific settings in ghc and ghci. hydra-poc's shell.nix is
somewhat more standard.

shell.nix

@@ -1,37 +1,66 @@
-# shell.nix
-{ pkgs ? import <nixpkgs> { } }:
+# A very simple shell.nix file for setting up necessary build tools. This is
+# likely going to be updated using the iohk-specific nixpkgs and a haskel.nix
+# derivation of our cabal.project.
+{ compiler ? "ghc8104"
+  # Latest haskell.nix for more likely cache hits
+, haskellNix ? import
+    (builtins.fetchTarball
+      "https://github.com/input-output-hk/haskell.nix/archive/abb289ff961fb1bd98eb0340088c432f15109807.tar.gz")
+    { }
+  # Use same pkgs as haskell.nix for more likely cache hits
+, nixpkgsSrc ? haskellNix.sources.nixpkgs-2009
+, nixpkgsArgs ? haskellNix.nixpkgsArgs
+, pkgs ? import nixpkgsSrc nixpkgsArgs
+  # Use cardano-node master for more likely cache hits
+}:
+with pkgs;
 let
-  hsPkgs = import ./default.nix { };
+  hls = haskell-nix.tool compiler "haskell-language-server" "latest";
+  ghc = haskell-nix.compiler.${compiler};
+  fourmolu = haskell-nix.tool compiler "fourmolu" "latest";
+  cabal-plan = pkgs.haskellPackages.cabal-plan ;
+  ghcid = pkgs.haskellPackages.ghcid ;
+  hspec-discover = pkgs.haskellPackages.hspec-discover ;
+  libsodium-vrf = libsodium.overrideAttrs (oldAttrs: {
+    name = "libsodium-1.0.18-vrf";
+    src = fetchFromGitHub {
+      owner = "input-output-hk";
+      repo = "libsodium";
+      # branch tdammers/rebased-vrf
+      rev = "66f017f16633f2060db25e17c170c2afa0f2a8a1";
+      sha256 = "12g2wz3gyi69d87nipzqnq4xc6nky3xbmi2i2pb2hflddq8ck72f";
+    };
+    nativeBuildInputs = [ autoreconfHook ];
+    configureFlags = "--enable-static";
+  });
 in
-hsPkgs.shellFor {
-  # Include only the *local* packages of your project.
-  packages = ps: with ps; [
-    hydra-sim
-  ];
-
-  # Builds a Hoogle documentation index of all dependencies,
-  # and provides a "hoogle" command to search the index.
-  #    withHoogle = true;
-
-  # You might want some extra tools in the shell (optional).
-
-  # Some common tools can be added with the `tools` argument
-  tools = {
-    cabal = "3.2.0.0";
-    hlint = "latest";
-    haskell-language-server = "latest";
-    ormolu = "latest";
-  };
-  # See overlays/tools.nix for more details
+mkShell rec {
+  name = "hydra-sim-env";
 
-  # Some you may need to get some other way.
-  buildInputs = with pkgs.haskellPackages; [
+  tools = [
+    cabal-install
+    fourmolu
     ghcid
+    ghc
+    hls
+    cabal-plan
+    # needed for HLS to work properly, see https://github.com/haskell/haskell-language-server/issues/176
     hspec-discover
+    # For discovering libs (below)
+    pkgconfig
   ];
 
-  # Setting it to true prevents cabal from choosing alternate plans, so that
-  # *all* dependencies are provided by Nix.
-  # However, this breaks hspec-discover so ¯\_(ツ)_/¯
-  exactDeps = false;
+  libs = [
+    libsodium-vrf
+    zlib
+  ];
+
+  buildInputs = tools ++ libs;
+
+  # Ensure that libz.so and other libraries are available to TH splices.
+  LD_LIBRARY_PATH = lib.makeLibraryPath libs;
+
+  # Force a UTF-8 locale because many Haskell programs and tests
+  # assume this.
+  LANG = "en_US.UTF-8";
 }