Extract node_modules building

Building the `node_modules` folder is not actually purescript specific
and is more of an input so this commit splits off the use of
npmlock2nix for building a `node_modules` output to node_modules.nix and
a `buildNodeModules` function in `plutus.lib.buildNodeModules`

nix/lib/node_modules.nix

@@ -0,0 +1,28 @@
+{ npmlock2nix
+, nodejs
+, python2
+, stdenv
+, lib
+, CoreServices ? null # needed by darwin only
+, xcodebuild ? null   # needed by darwin only
+}:
+let
+  # Takes a source and extracts `package.json, package-lock.json` from it
+  # Type: Path -> Path
+  getPackageFiles = src: lib.cleanSourceWith {
+    filter = (path: type: lib.elem (baseNameOf path) [ "package.json" "package-lock.json" ]);
+    inherit src;
+  };
+in
+# Description: Takes a `projectDir` path to a directory containing a `package.json` and a `package-lock.json`
+  # and creates an output containing `node_modules/, package.json, package-lock.json`. The `buildInputs`
+  # will be avaibale during `npm install`
+  # Type: Attr { projectDir: Path, buildInputs: List } -> Derivation
+{ projectDir, buildInputs ? [ ] }:
+npmlock2nix.node_modules {
+  inherit nodejs;
+  src = getPackageFiles projectDir;
+  buildInputs = [ python2 ]
+    ++ lib.optionals (stdenv.isDarwin) [ CoreServices xcodebuild ]
+    ++ buildInputs;
+}

nix/lib/purescript.nix

@@ -1,27 +1,19 @@
 { stdenv
 , lib
-, cacert
 , nodejs
-, nodePackages
-, python2
-, git
-, fetchurl
-, npmlock2nix
-, nodejs-headers
 , easyPS
-, CoreServices ? null # darwin only
-, xcodebuild ? null # darwin only
+, buildNodeModules
 }:
 
 { psSrc
 , src
 , name
 , additionalPurescriptSources ? [ ]
+, additionalNpmBuildInputs ? [ ]
 , packages
 , spagoPackages
 , webCommon
 , checkPhase ? ""
-, passthru ? { }
 }:
 let
   cleanSrcs = lib.cleanSourceWith {
@@ -33,28 +25,19 @@ let
     };
   };
 
-  packageLockJson = lib.cleanSourceWith {
-    filter = (path: type: lib.elem (baseNameOf path) [ "package.json" "package-lock.json" ]);
-    inherit src;
-  };
-
   purescriptSources = [
     "src/**/*.purs"
     "test/**/*.purs"
     "generated/**/*.purs"
     ".spago/*/*/src/**/*.purs"
   ] ++ additionalPurescriptSources;
 
-  nodeModules = npmlock2nix.node_modules {
-    inherit nodejs;
-    src = packageLockJson;
-    buildInputs = [ python2 ] ++ lib.optionals (stdenv.isDarwin) [ CoreServices xcodebuild ];
-  };
+  nodeModules = buildNodeModules { projectDir = src; buildInputs = additionalNpmBuildInputs; };
 in
 stdenv.mkDerivation {
   name = "plutus-playground-client";
   src = cleanSrcs;
-  buildInputs = [ nodeModules easyPS.purs easyPS.spago easyPS.psc-package python2 ];
+  buildInputs = [ nodeModules easyPS.purs easyPS.spago easyPS.psc-package ];
   buildPhase = ''
     export HOME=$NIX_BUILD_TOP
     shopt -s globstar

nix/pkgs/default.nix

@@ -147,16 +147,15 @@ let
     haddock-combine = pkgs.callPackage ../lib/haddock-combine.nix { inherit sphinxcontrib-haddock; };
     latex = pkgs.callPackage ../lib/latex.nix { };
     npmlock2nix = (import sources.npmlock2nix { });
-    buildPursPackage = pkgs.callPackage ../lib/purescript.nix ({
-      inherit easyPS nodejs-headers npmlock2nix;
-      CoreServices = if stdenv.isDarwin then pkgs.darwin.apple_sdk.frameworks.CoreServices else null;
-      xcodebuild = if stdenv.isDarwin then pkgs.xcodebuild else null;
+    buildPursPackage = pkgs.callPackage ../lib/purescript.nix { inherit easyPS buildNodeModules;inherit (pkgs) nodejs; };
+    buildNodeModules = pkgs.callPackage ../lib/node_modules.nix ({
+      inherit npmlock2nix;
     } // pkgs.lib.optionalAttrs (stdenv.isDarwin) {
-      inherit (pkgs.darwin.apple_sdk.frameworks) CoreServices;
-      inherit (pkgs) xcodebuild;
+      CoreServices = pkgs.darwin.apple_sdk.frameworks.CoreServices;
+      xcodebuild = pkgs.xcodebuild;
     });
-  };
 
+  };
 
 in
 {