Fix emoji URLs in Markdown when relative_url_root is used

Also adds the ability to run rspecs with relative_url_defined on the enviornment. For example:

RELATIVE_URL_ROOT=/gitlab rspec

Closes #1728

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 v 8.0.0 (unreleased)
+  - Fix emoji URLs in Markdown when relative_url_root is used (Stan Hu)
   - Omit filename in Content-Disposition header in raw file download to avoid RFC 6266 encoding issues (Stan HU)
   - Prevent anchors from being hidden by header (Stan Hu)
   - Fix bug where only the first 15 Bitbucket issues would be imported (Stan Hu)

lib/gitlab/markdown.rb

@@ -77,7 +77,7 @@ module Gitlab
         pipeline: options[:pipeline],
         # EmojiFilter
-        asset_root: Gitlab.config.gitlab.url,
+        asset_root: Gitlab.config.gitlab.base_url,
         asset_host: Gitlab::Application.config.asset_host,
         # TableOfContentsFilter

spec/spec_helper.rb

@@ -28,6 +28,7 @@ RSpec.configure do |config|
   config.include LoginHelpers,        type: :feature
   config.include LoginHelpers,        type: :request
   config.include StubConfiguration
+  config.include RelativeUrl,         type: feature
   config.include TestEnv
   config.infer_spec_type_from_file_location!

spec/support/matchers/markdown_matchers.rb

@@ -27,6 +27,9 @@ module MarkdownMatchers
     match do |actual|
       expect(actual).to have_selector('img.emoji', count: 10)
+
+      image = actual.at_css('img.emoji')
+      expect(image['src'].to_s).to start_with(Gitlab.config.gitlab.url + '/assets')
     end
   end

spec/support/relative_url.rb

+# Fix route helpers in tests (e.g. root_path, ...)
+module RelativeUrl
+  extend ActiveSupport::Concern
+
+  included do
+    default_url_options[:script_name] = Rails.application.config.relative_url_root
+  end
+end