merge_requests: add fetch command to the MR page

CHANGELOG

@@ -7,6 +7,7 @@ v 7.14.0 (unreleased)
   - Set OmniAuth full_host parameter to ensure redirect URIs are correct (Stan Hu)
   - Expire Rails cache entries after two weeks to prevent endless Redis growth
   - Add support for destroying project milestones (Stan Hu)
+  - Add fetch command to the MR page.
 
 v 7.13.0 (unreleased)
   - Only enable HSTS header for HTTPS and port 443 (Stan Hu)

app/views/projects/merge_requests/_show.html.haml

@@ -31,6 +31,16 @@
               %li= link_to "Email Patches", merge_request_path(@merge_request, format: :patch)
               %li= link_to "Plain Diff",    merge_request_path(@merge_request, format: :diff)
 
+    - if @merge_request.open? and @merge_request.source_branch_exists?
+      .append-bottom-20
+        .slead
+          %span
+            Fetch the branch with
+            %strong.label-branch<
+              git fetch
+              \ #{@merge_request.source_project.http_url_to_repo}
+              \ #{@merge_request.source_branch}
+
     = render "projects/merge_requests/show/how_to_merge"
     = render "projects/merge_requests/widget/show.html.haml"