Add a separate CI/CD pipeline retry service class

app/models/ci/pipeline.rb

@@ -234,7 +234,9 @@ module Ci
     end
 
     def mark_as_processable_after_stage(stage_idx)
-      builds.skipped.where('stage_idx > ?', stage_idx).find_each(&:process)
+      builds.skipped
+        .where('stage_idx > ?', stage_idx)
+        .find_each(&:process)
     end
 
     def latest?

app/services/ci/retry_pipeline_service.rb

+module Ci
+  class RetryPipelineService
+    include Gitlab::Allowable
+
+    def initialize(pipeline, user)
+      @pipeline = pipeline
+      @user = user
+    end
+
+    def execute
+      unless can?(@user, :update_pipeline, @pipeline)
+        raise Gitlab::Access::AccessDeniedError
+      end
+
+      @pipeline.stages.each do |stage|
+        stage.builds.failed_or_canceled.find_each do |build|
+          Ci::Build.retry(build, @user)
+        end
+      end
+    end
+  end
+end

spec/services/ci/retry_pipeline_service_spec.rb

+require 'spec_helper'
+
+describe Ci::RetryPipelineService, '#execute', :services do
+  let(:user) { create(:user) }
+  let(:project) { create(:empty_project) }
+  let(:pipeline) { create(:ci_pipeline, project: project) }
+  let(:service) { described_class.new(pipeline, user) }
+
+  context 'when user has ability to modify pipeline' do
+    let(:user) { create(:admin) }
+
+    context 'when there are failed builds in the last stage' do
+      before do
+        create_build(name: 'rspec 1', status: :success, stage_num: 0)
+        create_build(name: 'rspec 2', status: :failed, stage_num: 1)
+        create_build(name: 'rspec 3', status: :canceled, stage_num: 1)
+      end
+
+      it 'enqueues all builds in the last stage' do
+        service.execute
+
+        expect(build('rspec 2')).to be_pending
+        expect(build('rspec 3')).to be_pending
+      end
+    end
+  end
+
+  context 'when user is not allowed to retry pipeline' do
+    it 'raises an error' do
+      expect { service.execute }
+        .to raise_error Gitlab::Access::AccessDeniedError
+    end
+  end
+
+  def build(name)
+    pipeline.statuses.find_by(name: name)
+  end
+
+  def create_build(name:, status:, stage_num:)
+    create(:ci_build, name: name,
+                      status: status,
+                      stage: "stage_#{stage_num}",
+                      stage_idx: stage_num,
+                      pipeline: pipeline) do |build|
+      pipeline.update_status
+    end
+  end
+end