fix: remove middleman-sprockets and govuk_template

middleman-sprockets is deprecated[1] so remove all of our terrible
hacks and stick with SASS import statements. Remove the hard
dependency on SASS as well since Middleman ships with it. Remove the
govuk_template dependency as we don't use it either.

This will also make the bundle smaller and faster (the node_modules
folder is +8M smaller).

[1]: middleman/middleman-sprockets#132 (comment)

Gemfile

@@ -11,7 +11,3 @@ gem 'tzinfo-data', platforms: [:mswin, :mingw, :jruby]
 # Middleman Gems
 gem 'middleman', '>= 4.0.0'
 gem 'middleman-livereload'
-gem "middleman-sprockets"
-gem 'sprockets', '4.0.0'
-gem 'sass'
-gem 'sassc'

Gemfile.lock

@@ -74,9 +74,6 @@ GEM
       em-websocket (~> 0.5.1)
       middleman-core (>= 3.3)
       rack-livereload (~> 0.3.15)
-    middleman-sprockets (4.1.1)
-      middleman-core (~> 4.0)
-      sprockets (>= 3.0)
     minitest (5.11.3)
     padrino-helpers (0.13.3.4)
       i18n (~> 0.6, >= 0.6.7)
@@ -92,17 +89,9 @@ GEM
     rb-fsevent (0.10.3)
     rb-inotify (0.10.0)
       ffi (~> 1.0)
-    sass (3.7.4)
-      sass-listen (~> 4.0.0)
-    sass-listen (4.0.0)
-      rb-fsevent (~> 0.9, >= 0.9.4)
-      rb-inotify (~> 0.9, >= 0.9.7)
     sassc (2.2.1)
       ffi (~> 1.9)
     servolux (0.13.0)
-    sprockets (4.0.0)
-      concurrent-ruby (~> 1.0)
-      rack (> 1, < 3)
     temple (0.8.1)
     thor (0.20.3)
     thread_safe (0.3.6)
@@ -118,10 +107,6 @@ PLATFORMS
 DEPENDENCIES
   middleman (>= 4.0.0)
   middleman-livereload
-  middleman-sprockets
-  sass
-  sassc
-  sprockets (= 4.0.0)
   tzinfo-data
   wdm (~> 0.1.0)
 

config.rb

@@ -51,45 +51,3 @@ def get_nav_active_class(url, root_scope)
     'govuk-header__navigation-item--active' if current_page.url.start_with? (root_scope or url)
   end
 end
-
-# Build-specific configuration
-configure :build do
-  # Minify CSS on build
-  # activate :minify_css
-
-  # Minify Javascript on build
-  # activate :minify_javascript
-end
-
-# Override generated asset path to remove the long explicit vendor paths
-class ImportedAssetPathProcessor
-  attr_reader :app
-
-  def initialize(app)
-    @app = app
-  end
-
-  def call(sprockets_asset)
-    filename = File.basename(sprockets_asset.logical_path)
-    directory = case sprockets_asset.logical_path
-                # I fought the asset pipeline and the asset pipeline won:
-                # This first `when` statement handles an edge case where images are nested inside
-                # a stylesheets directory, as is the case in govuk_template.
-                when /stylesheets\/images\// then ([app.config[:images_dir]] * 2).join('/')
-                when /images\// then app.config[:images_dir]
-                when /fonts\// then app.config[:fonts_dir]
-                when /stylesheets\// then app.config[:css_dir]
-                else
-                  "assets"
-                end
-
-    File.join(directory, filename)
-  end
-end
-
-activate :sprockets do |config|
-  config.expose_middleman_helpers = true
-  config.imported_asset_path = ImportedAssetPathProcessor.new(app)
-end
-
-sprockets.append_path File.join(root, "node_modules")