Remove git refs used internally by GitLab from network graph

Closes #2702

CHANGELOG

@@ -7,6 +7,7 @@ v 8.0.2 (unreleased)
   - Make commit graphs responsive to window width changes (Stan Hu)
   - Fix top margin for sign-in button on public pages
   - Fix LDAP attribute mapping
+  - Remove git refs used internally by GitLab from network graph (Stan Hu)
 v 8.0.1
   - Improve CI migration procedure and documentation

app/helpers/graph_helper.rb

 module GraphHelper
   def get_refs(repo, commit)
     refs = ""
-    refs << commit.ref_names(repo).join(' ')
+    # Commit::ref_names already strips the refs/XXX from important refs (e.g. refs/heads/XXX)
+    # so anything leftover is internally used by GitLab
+    commit_refs = commit.ref_names(repo).reject{ |name| name.starts_with?('refs/') }
+    refs << commit_refs.join(' ')
     # append note count
     refs << "[#{@graph.notes[commit.id]}]" if @graph.notes[commit.id] > 0

spec/helpers/graph_helper_spec.rb

+require 'spec_helper'
+
+describe GraphHelper do
+  describe '#get_refs' do
+    let(:project) { create(:project) }
+    let(:commit)  { project.commit("master") }
+    let(:graph) { Network::Graph.new(project, 'master', commit, '') }
+
+    it 'filter our refs used by GitLab' do
+      allow(commit).to receive(:ref_names).and_return(['refs/merge-requests/abc', 'master', 'refs/tmp/xyz'])
+      self.instance_variable_set(:@graph, graph)
+      refs = get_refs(project.repository, commit)
+      expect(refs).to eq('master')
+    end
+  end
+end