Icon Sprite URL is also local even if asset_host is set

app/helpers/icons_helper.rb

 module IconsHelper
   extend self
+  include Gitlab::CurrentSettings
   include FontAwesome::Rails::IconHelper
 
   # Creates an icon tag given icon name(s) and possible icon modifiers.
@@ -23,10 +24,17 @@ module IconsHelper
     render "shared/icons/#{icon_name}.svg", size: size
   end
 
+  def sprite_icon_path
+    # SVG Sprites currently don't work across domains, so in the case of a CDN
+    # we have to set the current path deliberately to prevent addition of asset_host
+    sprite_base_url = ActionController::Base.asset_host.present? ? Gitlab.config.gitlab.url : nil
+    ActionController::Base.helpers.image_path('icons.svg', host: sprite_base_url)
+  end
+
   def sprite_icon(icon_name, size: nil, css_class: nil)
     css_classes = size ? "s#{size}" : ""
     css_classes << " #{css_class}" unless css_class.blank?
-    content_tag(:svg, content_tag(:use, "", { "xlink:href" => "#{image_path('icons.svg')}##{icon_name}" } ), class: css_classes.empty? ? nil : css_classes)
+    content_tag(:svg, content_tag(:use, "", { "xlink:href" => "#{sprite_icon_path()}##{icon_name}" } ), class: css_classes.empty? ? nil : css_classes)
   end
 
   def audit_icon(names, options = {})

lib/gitlab/gon_helper.rb

@@ -20,7 +20,7 @@ module Gitlab
       gon.gitlab_url             = Gitlab.config.gitlab.url
       gon.revision               = Gitlab::REVISION
       gon.gitlab_logo            = ActionController::Base.helpers.asset_path('gitlab_logo.png')
-      gon.sprite_icons           = ActionController::Base.helpers.asset_path('icons.svg')
+      gon.sprite_icons           = IconsHelper.sprite_icon_path
 
       if current_user
         gon.current_user_id = current_user.id

spec/helpers/icons_helper_spec.rb

@@ -16,6 +16,27 @@ describe IconsHelper do
     end
   end
 
+  describe 'sprite_icon' do
+    it 'returns relative path' do
+      expect(sprite_icon_path())
+        .to eq "/image/icons.svg"
+    end
+
+    context 'when an asset_host is set in the config it will return an absolute local URL' do
+      let(:asset_host) { 'http://assets' }
+
+      before do
+        allow(ActionController::Base).to receive(:asset_host).and_return(asset_host)
+      end
+
+      it 'returns an absolute URL on that asset host' do
+        gitlab_url = Gitlab.config.gitlab.url
+        expect(sprite_icon_path())
+          .to eq "#{gitlab_url}/image/icons.svg"
+      end
+    end
+  end
+
   describe 'sprite_icon' do
     icon_name = 'clock'