packaging: Backport bower support utilities

To support nixos-16.03 the utilities to build bower components are backported
inside of this PR. Once we switch to the new stable branch, we should be able to
drop these pieces again.

pkgs/backport-16.03-build-bower-components.nix

@@ -0,0 +1,60 b''
+# Backported buildBowerComponents so that we can also use it with the version
+# 16.03 which is the current stable at the time of this writing.
+#
+# This file can be removed once building with 16.03 is not needed anymore.
+
+{ pkgs }:
+
+{ buildInputs ? [], generated, ... } @ attrs:
+
+let
+  fetchbower = import ./backport-16.03-fetchbower.nix {
+    inherit (pkgs) stdenv lib;
+    inherit (pkgs.nodePackages) bower2nix;
+  };
+
+  # Fetches the bower packages. `generated` should be the result of a
+  # `bower2nix` command.
+  bowerPackages = import generated {
+    inherit (pkgs) buildEnv;
+    inherit 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/backport-16.03-fetchbower.nix

@@ -0,0 +1,26 b''
+{ stdenv, lib, bower2nix }:
+let
+  bowerVersion = version:
+    let
+      components = lib.splitString "#" version;
+      hash = lib.last components;
+      ver = if builtins.length components == 1 then version else hash;
+    in ver;
+
+  fetchbower = name: version: target: outputHash: stdenv.mkDerivation {
+    name = "${name}-${bowerVersion version}";
+    buildCommand = ''
+      fetch-bower --quiet --out=$PWD/out "${name}" "${target}" "${version}"
+      # In some cases, the result of fetchBower is different depending
+      # on the output directory (e.g. if the bower package contains
+      # symlinks). So use a local output directory before copying to
+      # $out.
+      cp -R out $out
+    '';
+    outputHashMode = "recursive";
+    outputHashAlgo = "sha256";
+    inherit outputHash;
+    buildInputs = [ bower2nix ];
+  };
+
+in fetchbower

default.nix

@@ -30,6 +30,10 b' let'
     then pythonPackages
     else getAttr pythonPackages pkgs;
 
+  buildBowerComponents =
+    pkgs.buildBowerComponents or
+    (import ./pkgs/backport-16.03-build-bower-components.nix { inherit pkgs; });
+
   elem = builtins.elem;
   basename = path: with pkgs.lib; last (splitString "/" path);
   startsWith = prefix: full: let
@@ -58,7 +62,7 b' let'
   };
   nodeDependencies = nodeEnv.shell.nodeDependencies;
 
-  bowerComponents = pkgs.buildBowerComponents {
+  bowerComponents = buildBowerComponents {
     name = "enterprise-ce-${version}";
     generated = ./pkgs/bower-packages.nix;
     src = rhodecode-enterprise-ce-src;