Add feature flag disable_keep_around_refs

This feature flag allows keep-around refs to be turned off for specific
repositories. Note that while this feature is enabled, the keep-around
refs that would have been created will never be created.

config/feature_flags/ops/disable_keep_around_refs.yml

+---
+name: disable_keep_around_refs
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/124123
+rollout_issue_url:
+milestone: '16.1'
+type: ops
+group: group::gitaly
+default_enabled: false

lib/gitlab/git/keep_around.rb

@@ -19,6 +19,8 @@ def initialize(repository)
       end
 
       def execute(shas)
+        return if disabled?
+
         shas.uniq.each do |sha|
           next unless sha.present? && commit_by(oid: sha)
 
@@ -32,6 +34,8 @@ def execute(shas)
       end
 
       def kept_around?(sha)
+        return true if disabled?
+
         ref_exists?(keep_around_ref_name(sha))
       end
 
@@ -40,6 +44,11 @@ def kept_around?(sha)
 
       private
 
+      def disabled?
+        Feature.enabled?(:disable_keep_around_refs, @repository, type: :ops) ||
+          (@repository.project && Feature.enabled?(:disable_keep_around_refs, @repository.project, type: :ops))
+      end
+
       def keep_around_ref_name(sha)
         "refs/#{::Repository::REF_KEEP_AROUND}/#{sha}"
       end

spec/lib/gitlab/git/keep_around_spec.rb

@@ -7,6 +7,7 @@
 
   let(:repository) { create(:project, :repository).repository }
   let(:service) { described_class.new(repository) }
+  let(:keep_around_ref_name) { "refs/#{::Repository::REF_KEEP_AROUND}/#{sample_commit.id}" }
 
   it "does not fail if we attempt to reference bad commit" do
     expect(service.kept_around?('abc1234')).to be_falsey
@@ -16,6 +17,7 @@
     service.execute([sample_commit.id])
 
     expect(service.kept_around?(sample_commit.id)).to be_truthy
+    expect(repository.list_refs([keep_around_ref_name])).not_to be_empty
   end
 
   it "does not fail if writting the ref fails" do
@@ -45,4 +47,17 @@
       expect(service.kept_around?(another_sample_commit.id)).to be_truthy
     end
   end
+
+  context 'when disable_keep_around_refs feature flag is enabled' do
+    before do
+      stub_feature_flags(disable_keep_around_refs: true)
+    end
+
+    it 'does not create keep-around refs' do
+      service.execute([sample_commit.id])
+
+      expect(service.kept_around?(sample_commit.id)).to be_truthy
+      expect(repository.list_refs([keep_around_ref_name])).to be_empty
+    end
+  end
 end

spec/spec_helper.rb

@@ -312,6 +312,9 @@
       # most cases. We do test the email verification flow in the appropriate specs.
       stub_feature_flags(require_email_verification: false)
 
+      # Keep-around refs should only be turned off for specific projects/repositories.
+      stub_feature_flags(disable_keep_around_refs: false)
+
       allow(Gitlab::GitalyClient).to receive(:can_use_disk?).and_return(enable_rugged)
     else
       unstub_all_feature_flags