Fix asset pipeline with libsass

Using a sass css compressor causes a scss file to be processed twice
(once to build, once to compress) which breaks the usage of "unquote"
to use CSS that has same function names as SCSS such as max.

config/application.rb

@@ -109,6 +109,12 @@ class Application < Rails::Application
     # Path within public/ where assets are compiled to
     config.assets.prefix = "/assets/government-frontend"
 
+    # Using a sass css compressor causes a scss file to be processed twice
+    # (once to build, once to compress) which breaks the usage of "unquote"
+    # to use CSS that has same function names as SCSS such as max.
+    # https://github.com/alphagov/govuk-frontend/issues/1350
+    config.assets.css_compressor = nil
+
     # allow overriding the asset host with an enironment variable, useful for
     # when router is proxying to this app but asset proxying isn't set up.
     config.asset_host = ENV["ASSET_HOST"]

config/environments/production.rb

@@ -28,6 +28,10 @@
   # Do not fallback to assets pipeline if a precompiled asset is missed.
   config.assets.compile = false
 
+  # Rather than use a CSS compressor, use the SASS style to perform compression.
+  config.sass.style = :compressed
+  config.sass.line_comments = false
+
   # Enable serving of images, stylesheets, and JavaScripts from an asset server.
   # config.action_controller.asset_host = 'http://assets.example.com'