Don't use rugged in Repository#refs_hash

The refs hash is used to determine what branches and tags have a commit
as head in the network graph. The previous implementation depended on
Rugged#references. The problem with this implementation was that it
depended on rugged, but also that it iterated over all references and
thus loading more data than needed if for example the project uses CI/CD
environments, Pipelines, or Merge Requests.

Given only refs are checked the network cares about the GraphHelper#refs
method has no need to reject those, simplifying the method.

Closes gitlab-org/gitaly#880

app/helpers/graph_helper.rb

 module GraphHelper
-  def get_refs(repo, commit)
-    refs = ""
-    # 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(' ')
+  def refs(repo, commit)
+    refs = commit.ref_names(repo).join(' ')
 
     # append note count
     notes_count = @graph.notes[commit.id]

app/views/projects/network/show.json.erb

@@ -13,7 +13,7 @@
         },
         time: c.time,
         space: c.spaces.first,
-        refs: get_refs(@graph.repo, c),
+        refs: refs(@graph.repo, c),
         id: c.sha,
         date: c.date,
         message: c.message,

lib/gitlab/git/commit.rb

@@ -402,15 +402,6 @@ module Gitlab
         end
       end
 
-      # Get a collection of Rugged::Reference objects for this commit.
-      #
-      # Ex.
-      #   commit.ref(repo)
-      #
-      def refs(repo)
-        repo.refs_hash[id]
-      end
-
       # Get ref names collection
       #
       # Ex.
@@ -418,7 +409,7 @@ module Gitlab
       #
       def ref_names(repo)
         refs(repo).map do |ref|
-          ref.name.sub(%r{^refs/(heads|remotes|tags)/}, "")
+          ref.sub(%r{^refs/(heads|remotes|tags)/}, "")
         end
       end
 
@@ -553,6 +544,15 @@ module Gitlab
           date: Google::Protobuf::Timestamp.new(seconds: author_or_committer[:time].to_i)
         )
       end
+
+      # Get a collection of Gitlab::Git::Ref objects for this commit.
+      #
+      # Ex.
+      #   commit.ref(repo)
+      #
+      def refs(repo)
+        repo.refs_hash[id]
+      end
     end
   end
 end

lib/gitlab/git/repository.rb

@@ -627,21 +627,18 @@ module Gitlab
         end
       end
 
-      # Get refs hash which key is SHA1
-      # and value is a Rugged::Reference
+      # Get refs hash which key is is the commit id
+      # and value is a Gitlab::Git::Tag or Gitlab::Git::Branch
+      # Note that both inherit from Gitlab::Git::Ref
       def refs_hash
-        # Initialize only when first call
-        if @refs_hash.nil?
+        return @refs_hash if @refs_hash
+
         @refs_hash = Hash.new { |h, k| h[k] = [] }
 
-          rugged.references.each do |r|
-            # Symbolic/remote references may not have an OID; skip over them
-            target_oid = r.target.try(:oid)
-            if target_oid
-              sha = rev_parse_target(target_oid).oid
-              @refs_hash[sha] << r
-            end
-          end
+        (tags + branches).each do |ref|
+          next unless ref.target && ref.name
+
+          @refs_hash[ref.dereferenced_target.id] << ref.name
         end
 
         @refs_hash

spec/helpers/graph_helper_spec.rb

@@ -7,10 +7,10 @@ describe GraphHelper do
     let(:graph) { Network::Graph.new(project, 'master', commit, '') }
 
     it 'filters 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')
+      refs = refs(project.repository, commit)
+
+      expect(refs).to match('master')
     end
   end
 end

spec/lib/gitlab/git/repository_spec.rb

@@ -600,12 +600,16 @@ describe Gitlab::Git::Repository, seed_helper: true do
   end
 
   describe "#refs_hash" do
-    let(:refs) { repository.refs_hash }
+    subject { repository.refs_hash }
 
     it "should have as many entries as branches and tags" do
       expected_refs = SeedRepo::Repo::BRANCHES + SeedRepo::Repo::TAGS
       # We flatten in case a commit is pointed at by more than one branch and/or tag
-      expect(refs.values.flatten.size).to eq(expected_refs.size)
+      expect(subject.values.flatten.size).to eq(expected_refs.size)
+    end
+
+    it 'has valid commit ids as keys' do
+      expect(subject.keys).to all( match(Commit::COMMIT_SHA_PATTERN) )
     end
   end