Render cross reference in issue title

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/stylesheets/generic/issue_box.scss

@@ -113,6 +113,11 @@
     padding: 10px 15px;
   }
 
+  .cross-project-ref {
+    float: left;
+    padding: 10px 15px;
+  }
+
   .creator {
     float: right;
     padding: 10px 15px;

app/helpers/gitlab_markdown_helper.rb

@@ -254,4 +254,16 @@ module GitlabMarkdownHelper
       truncated
     end
   end
+
+  def cross_project_reference(project, entity)
+    path = project.path_with_namespace
+
+    if entity.kind_of?(Issue)
+      [path, entity.iid].join('#')
+    elsif entity.kind_of?(MergeRequest)
+      [path, entity.iid].join('!')
+    else
+      raise 'Not supported type'
+    end
+  end
 end

app/views/projects/issues/show.html.haml

@@ -38,6 +38,9 @@
       - else
         Open
 
+    .cross-project-ref
+      = cross_project_reference(@project, @issue)
+
     .creator
       Created by #{link_to_member(@project, @issue.author)} #{issue_timestamp(@issue)}