Revert "Merge branch 'remove-depend_on_persistent_pipeline_ref-feature-flag' into 'master'"

This reverts merge request !18185

app/models/ci/persistent_ref.rb

@@ -14,13 +14,15 @@ module Ci
     delegate :ref_exists?, :create_ref, :delete_refs, to: :repository
 
     def exist?
+      return unless enabled?
+
       ref_exists?(path)
     rescue
       false
     end
 
     def create
-      return if exist?
+      return unless enabled? && !exist?
 
       create_ref(sha, path)
     rescue => e
@@ -29,6 +31,8 @@ module Ci
     end
 
     def delete
+      return unless enabled?
+
       delete_refs(path)
     rescue Gitlab::Git::Repository::NoRepository
       # no-op
@@ -40,5 +44,11 @@ module Ci
     def path
       "refs/#{Repository::REF_PIPELINES}/#{pipeline.id}"
     end
+
+    private
+
+    def enabled?
+      Feature.enabled?(:depend_on_persistent_pipeline_ref, project)
+    end
   end
 end

doc/ci/pipelines.md

@@ -468,3 +468,15 @@ To illustrate its life cycle:
    even if the commit history of the `example` branch has been overwritten by force-push.
 1. GitLab Runner fetches the persistent pipeline ref and gets source code from the checkout-SHA.
 1. When the pipeline finished, its persistent ref is cleaned up in a background process.
+
+NOTE: **NOTE**: At this moment, this feature is off dy default and can be manually enabled
+by enabling `depend_on_persistent_pipeline_ref` feature flag, however, we'd remove this
+feature flag and make it enabled by deafult by the day we release 12.4 _if we don't find any issues_.
+If you'd be interested in manually turning on this behavior, please ask the administrator
+to execute the following commands in rails console.
+
+```shell
+> sudo gitlab-rails console                                        # Login to Rails console of GitLab instance.
+> project = Project.find_by_full_path('namespace/project-name')    # Get the project instance.
+> Feature.enable(:depend_on_persistent_pipeline_ref, project)      # Enable the feature flag.
+```

spec/models/ci/persistent_ref_spec.rb

@@ -45,6 +45,18 @@ describe Ci::PersistentRef do
         expect(pipeline.persistent_ref).to be_exist
       end
 
+      context 'when depend_on_persistent_pipeline_ref feature flag is disabled' do
+        before do
+          stub_feature_flags(depend_on_persistent_pipeline_ref: false)
+        end
+
+        it 'does not create a persistent ref' do
+          expect(project.repository).not_to receive(:create_ref)
+
+          subject
+        end
+      end
+
       context 'when sha does not exist in the repository' do
         let(:sha) { 'not-exist' }