Add pkgs.buildBowerComponents function

pkgs/development/bower-modules/generic/default.nix

···
+{ pkgs }:
+
+{ buildInputs ? [], generated, ... } @ attrs:
+
+let
+  # Fetches the bower packages. `generated` should be the result of a
+  # `bower2nix` command.
+  bowerPackages = import generated {
+    inherit (pkgs) buildEnv fetchbower;
+  };
+
+in pkgs.stdenv.mkDerivation (
+  attrs
+  //
+  {
+    name = "bower_components-" + attrs.name;
+
+    inherit bowerPackages;
+
+    builder = builtins.toFile "builder.sh" ''
+      source $stdenv/setup
+
+      # The project's bower.json is required
+      cp $src/bower.json .
+
+      # Dereference symlinks -- bower doesn't like them
+      cp  --recursive --reflink=auto       \
+          --dereference --no-preserve=mode \
+          $bowerPackages bc
+
+      # Bower install in offline mode -- links together the fetched
+      # bower packages.
+      HOME=$PWD bower \
+          --config.storage.packages=bc/packages \
+          --config.storage.registry=bc/registry \
+          --offline install
+
+      # Sets up a single bower_components directory within
+      # the output derivation.
+      mkdir -p $out
+      mv bower_components $out
+    '';
+
+    buildInputs = buildInputs ++ [
+      pkgs.git
+      pkgs.nodePackages.bower
+    ];
+  }
+)

pkgs/top-level/all-packages.nix

···
 
   yuicompressor = callPackage ../development/tools/yuicompressor { };
 
+  ### DEVELOPMENT / BOWER MODULES (JAVASCRIPT)
+
+  buildBowerComponents = callPackage ../development/bower-modules/generic { };
+
   ### DEVELOPMENT / GO MODULES
 
   go14Packages = callPackage ./go-packages.nix {