Fixing a problem with the update-client-deps script.

There is a spago2nix in easyPS, but it doesn't (currently) work. It doesn't
matter because it's actually just a thin call to spago2nix's nix build
script. So we can just go directly to the source and get the latest
version.

nix/pkgs/default.nix

@@ -72,7 +72,7 @@ let
   updateHie = pkgs.callPackage ./update-hie { inherit gen-hie; };
   updateMetadataSamples = pkgs.callPackage ./update-metadata-samples { };
   updateClientDeps = pkgs.callPackage ./update-client-deps {
-    inherit (easyPS) purs psc-package spago spago2nix;
+    inherit purs psc-package spago spago2nix;
   };
 
   #
@@ -121,10 +121,17 @@ let
   # mean that e.g. we can't build the client dep updating
   # script on Darwin.
   easyPS = pkgs.callPackage (sources.easy-purescript-nix) { };
+
   # We pull out some packages from easyPS that are a pain to get otherwise.
   # In particular, we used to build purty ourselves, but now its build is a nightmare.
   # This does mean we can't as easily control the version we get, though.
-  inherit (easyPS) purty purs spago;
+  inherit (easyPS) purty purs psc-package spago;
+
+  # There is a spago2nix in easyPS, but it doesn't (currently) work. It doesn't
+  # matter because it's actually just a thin call to spago2nix's nix build
+  # script. So we can just go directly to the source and get the latest
+  # version.
+  spago2nix = pkgs.callPackage (sources.spago2nix) { };
 
   # sphinx haddock support
   sphinxcontrib-haddock = pkgs.callPackage (sources.sphinxcontrib-haddock) { pythonPackages = pkgs.python3Packages; };
@@ -172,7 +179,7 @@ in
   inherit sphinx-markdown-tables sphinxemoji sphinxcontrib-haddock;
   inherit nix-pre-commit-hooks;
   inherit haskell agdaPackages cabal-install stylish-haskell hlint haskell-language-server hie-bios gen-hie;
-  inherit purty purty-pre-commit purs spago;
+  inherit purty purty-pre-commit purs spago spago2nix;
   inherit fixPurty fixStylishHaskell updateMaterialized updateHie updateMetadataSamples updateClientDeps;
   inherit iohkNix set-git-rev web-ghc thorp;
   inherit easyPS plutus-haddock-combined;

nix/sources.json

@@ -127,6 +127,18 @@
         "url": "https://github.com/cachix/pre-commit-hooks.nix/archive/c7e3896e35ceea480a7484ec1709be7bdda8849d.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
+    "spago2nix": {
+        "branch": "master",
+        "description": "Generate a derivation of Spago dependencies, and use them to install them into the directory structure used by Spago.",
+        "homepage": "",
+        "owner": "justinwoo",
+        "repo": "spago2nix",
+        "rev": "898798204fa8f53837bbcf71e30aeb425deb0906",
+        "sha256": "1igb1ldilj52f6vppsv58hxwzasd9vjcfsfhxsmk1jhs7cbnb1dq",
+        "type": "tarball",
+        "url": "https://github.com/justinwoo/spago2nix/archive/898798204fa8f53837bbcf71e30aeb425deb0906.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
     "sphinxcontrib-haddock": {
         "branch": "master",
         "builtin": false,