fix nix evaluation impurities

default.nix

@@ -3,24 +3,30 @@
 , system ? builtins.currentSystem
 
 , haskellNix ? import
-    (builtins.fetchTarball
-      "https://github.com/input-output-hk/haskell.nix/archive/0.0.64.tar.gz")
-    { }
+    (builtins.fetchTarball {
+      url = "https://github.com/input-output-hk/haskell.nix/archive/0.0.64.tar.gz";
+      sha256 = "0mply6n3gym8r7z4l7512phw667qzwfqkfl1zmiyrdjpdg7xqn1d";
+    })
+    { pkgs = import nixpkgsSrc { inherit system; }; }
 
 , iohkNix ? import
-    (builtins.fetchTarball
-      "https://github.com/input-output-hk/iohk-nix/archive/d31417fe8c8fbfb697b3ad4c498e17eb046874b9.tar.gz")
+    (builtins.fetchTarball {
+      url = "https://github.com/input-output-hk/iohk-nix/archive/d31417fe8c8fbfb697b3ad4c498e17eb046874b9.tar.gz";
+      sha256 = "0w562wdmdhp83dw9rabiijj5hk1f4l8p8f3bwlr7virakgbg8lf8";
+    })
     { }
 
   # NOTE: use the 'repo' branch of CHaP which contains the index
-, CHaP ? (builtins.fetchTarball
-    "https://github.com/input-output-hk/cardano-haskell-packages/archive/ceaae5355c81453d7cb092acadec3441bf57ed11.tar.gz")
+, CHaP ? (builtins.fetchTarball {
+  url = "https://github.com/input-output-hk/cardano-haskell-packages/archive/ceaae5355c81453d7cb092acadec3441bf57ed11.tar.gz";
+  sha256 = "0pwlfv2gx7h2z492bfhbr6pakidi5i8dzpc4094sb05i9rrgyq32";
+})
 
-  # nixpkgs-unstable as also used by cardano-node, cardano-ledger et al
-, nixpkgsSrc ? haskellNix.sources.nixpkgs-unstable
+, nixpkgsSrc ? iohkNix.nixpkgs
 }:
 let
   pkgs = import nixpkgsSrc (haskellNix.nixpkgsArgs // {
+    inherit system;
     overlays =
       # Haskell.nix (https://github.com/input-output-hk/haskell.nix)
       haskellNix.overlays
@@ -62,7 +68,7 @@ let
       rev = "1.35.4";
       sha256 = "1j01m2cp2vdcl26zx9xmipr551v3b2rz9kfn9ik8byfwj1z7652r";
     })
-    { };
+    { inherit system; };
 in
 {
   inherit compiler pkgs hsPkgs cardano-node;

release.nix

@@ -3,10 +3,11 @@
 {
   # this is passed in by hydra to provide us with the revision
   hydra ? { outPath = ./.; rev = "abcdef"; }
+, system ? builtins.currentSystem
 , ...
 }:
 let
-  project = import ./default.nix { };
+  project = import ./default.nix { inherit system; };
   nativePkgs = project.hsPkgs;
   # Allow reinstallation of terminfo as it's not installed with cross compilers.
   patchedForCrossProject = project.hsPkgs.appendModule
@@ -15,7 +16,7 @@ let
 in
 rec {
   # Build shell derivation to cache it
-  shell = import ./shell.nix { };
+  shell = import ./shell.nix { inherit system; };
 
   # Build some executables
   hydra-node = nativePkgs.hydra-node.components.exes.hydra-node;

shell.nix

@@ -5,9 +5,10 @@
 {
   # Used in CI to have a smaller closure
   withoutDevTools ? false
+, system ? builtins.currentSystem
 }:
 let
-  project = import ./default.nix { };
+  project = import ./default.nix { inherit system; };
   inherit (project) compiler pkgs hsPkgs cardano-node;
 
   libs = [