Override servant version in default.nix

Also remove shell.nix

default.nix

-{ mkDerivation, aeson, base, bytestring, directory, mtl
-, optparse-applicative, optparse-generic, servant, servant-server
-, shelly, stdenv, text, warp, zlib
-}:
-mkDerivation {
-  pname = "terraform-http-backend-pass";
-  version = "0.1.0.0";
-  src = ./.;
-  isLibrary = true;
-  isExecutable = true;
-  libraryHaskellDepends = [
-    aeson base bytestring directory mtl optparse-applicative
-    optparse-generic servant servant-server shelly text warp
-  ];
-  librarySystemDepends = [ zlib ];
-  executableHaskellDepends = [ base ];
-  license = "unknown";
-  hydraPlatforms = stdenv.lib.platforms.none;
-}
+let sources = import ./nix/sources.nix;
+in { pkgs ? import sources.nixpkgs {},
+     compiler ? "ghc8103"
+   }:
+     let
+       servantPkgs = import sources.servant {inherit pkgs compiler; };
+       overrides = self: super: {
+         terraform-http-backend-pass = self.callCabal2nix "terraform-http-backend-pass" ./. {};
+         servant = servantPkgs.servant;
+         servant-server = servantPkgs.servant-server;
+       };
+       hPkgs = pkgs.haskell.packages.${compiler}.override { inherit overrides; };
+     in hPkgs.terraform-http-backend-pass

nix/sources.json

@@ -22,5 +22,17 @@
         "type": "tarball",
         "url": "https://github.com/NixOS/nixpkgs/archive/8542021fe7f9f777294649b1cdc853240806ff21.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "servant": {
+        "branch": "master",
+        "description": "Main repository for the servant libraries -- DSL for describing, serving, querying, mocking, documenting web applications and more!",
+        "homepage": "https://docs.servant.dev/",
+        "owner": "haskell-servant",
+        "repo": "servant",
+        "rev": "27173c922311112dd153346cf3cd72b9fb0f3551",
+        "sha256": "08lar7s9fi49qzkgrq55z6nc0khx1z36914d2f086wprx0wyrk0a",
+        "type": "tarball",
+        "url": "https://github.com/haskell-servant/servant/archive/27173c922311112dd153346cf3cd72b9fb0f3551.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     }
 }

shell.nix

-{ nixpkgs ? import <nixpkgs> {}, compiler ? "default", doBenchmark ? false }:
-
-let
-
-  inherit (nixpkgs) pkgs;
-
-  f = { mkDerivation, aeson, base, bytestring, directory, mtl
-      , optparse-applicative, optparse-generic, servant, servant-server
-      , shelly, stdenv, text, warp, zlib
-      }:
-      mkDerivation {
-        pname = "terraform-http-backend-pass";
-        version = "0.1.0.0";
-        src = ./.;
-        isLibrary = true;
-        isExecutable = true;
-        libraryHaskellDepends = [
-          aeson base bytestring directory mtl optparse-applicative
-          optparse-generic servant servant-server shelly text warp
-        ];
-        librarySystemDepends = [ zlib ];
-        executableHaskellDepends = [ base ];
-        license = "unknown";
-        hydraPlatforms = stdenv.lib.platforms.none;
-      };
-
-  haskellPackages = if compiler == "default"
-                       then pkgs.haskellPackages
-                       else pkgs.haskell.packages.${compiler};
-
-  variant = if doBenchmark then pkgs.haskell.lib.doBenchmark else pkgs.lib.id;
-
-  drv = variant (haskellPackages.callPackage f {});
-
-in
-
-  if pkgs.lib.inNixShell then drv.env else drv