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

2 files changed, 21 insertions, 24 deletions

diff --git a/lib/gitlab/git/commit.rb b/lib/gitlab/git/commit.rb
index 768617e2cae..d95561fe1b2 100644
--- a/lib/gitlab/git/commit.rb
+++ b/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
diff --git a/lib/gitlab/git/repository.rb b/lib/gitlab/git/repository.rb
index ab1362a3bb0..39279960154 100644
--- a/lib/gitlab/git/repository.rb
+++ b/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?
-          @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
+        return @refs_hash if @refs_hash
+
+        @refs_hash = Hash.new { |h, k| h[k] = [] }
+
+        (tags + branches).each do |ref|
+          next unless ref.target && ref.name
+
+          @refs_hash[ref.dereferenced_target.id] << ref.name
         end
 
         @refs_hash