Handle external issues in IssueReferenceFilter

IssueReferenceFilter will end up processing internal issue references
when a project uses an external issues tracker while still using
internal issue references (in the form of `#\d+`). This commit ensures
that these links are rendered as external issue links, regardless of
whether the project one currently views uses an internal or external
issues tracker.

Fixes gitlab-org/gitlab-ce#19036, gitlab-com/performance#16

lib/banzai/filter/abstract_reference_filter.rb

@@ -160,11 +160,7 @@ module Banzai
             title = object_link_title(object)
             klass = reference_class(object_sym)
-            data  = data_attribute(
-              original:     link_text || match,
-              project:      project.id,
-              object_sym => object.id
-            )
+            data = data_attributes_for(link_text || match, project, object)
             if matches.names.include?("url") && matches[:url]
               url = matches[:url]
@@ -183,6 +179,14 @@ module Banzai
         end
       end
+      def data_attributes_for(text, project, object)
+        data_attribute(
+          original:     text,
+          project:      project.id,
+          object_sym => object.id
+        )
+      end
+
       def object_link_text_extras(object, matches)
         extras = []

lib/banzai/filter/issue_reference_filter.rb

@@ -46,6 +46,26 @@ module Banzai
         end
       end
+      def object_link_title(object)
+        if object.is_a?(ExternalIssue)
+          "Issue in #{object.project.external_issue_tracker.title}"
+        else
+          super
+        end
+      end
+
+      def data_attributes_for(text, project, object)
+        if object.is_a?(ExternalIssue)
+          data_attribute(
+            project: project.id,
+            external_issue: object.id,
+            reference_type: ExternalIssueReferenceFilter.reference_type
+          )
+        else
+          super
+        end
+      end
+
       def find_projects_for_paths(paths)
         super(paths).includes(:gitlab_issue_tracker_service)
       end

lib/banzai/filter/reference_filter.rb

@@ -29,7 +29,7 @@ module Banzai
       def data_attribute(attributes = {})
         attributes = attributes.reject { |_, v| v.nil? }
-        attributes[:reference_type] = self.class.reference_type
+        attributes[:reference_type] ||= self.class.reference_type
         attributes.delete(:original) if context[:no_original_data]
         attributes.map { |key, value| %Q(data-#{key.to_s.dasherize}="#{escape_once(value)}") }.join(" ")
       end

spec/lib/banzai/filter/issue_reference_filter_spec.rb

@@ -199,6 +199,19 @@ describe Banzai::Filter::IssueReferenceFilter, lib: true do
     end
   end
+  context 'referencing external issues' do
+    let(:project) { create(:redmine_project) }
+
+    it 'renders internal issue IDs as external issue links' do
+      doc = reference_filter('#1')
+      link = doc.css('a').first
+
+      expect(link.attr('data-reference-type')).to eq('external_issue')
+      expect(link.attr('title')).to eq('Issue in Redmine')
+      expect(link.attr('data-external-issue')).to eq('1')
+    end
+  end
+
   describe '#issues_per_Project' do
     context 'using an internal issue tracker' do
       it 'returns a Hash containing the issues per project' do