Implement POC config based parallelization

app/models/ci/build.rb

@@ -801,10 +801,16 @@ module Ci
         variables.append(key: "CI_COMMIT_TAG", value: ref) if tag?
         variables.append(key: "CI_PIPELINE_TRIGGERED", value: 'true') if trigger_request
         variables.append(key: "CI_JOB_MANUAL", value: 'true') if action?
+        variables.append(key: "CI_NODE_INDEX", value: node_index.to_s) if self.options&.include?(:parallel)
+        variables.append(key: "CI_NODE_TOTAL", value: (self.options&.dig(:parallel) || 1).to_s)
         variables.concat(legacy_variables)
       end
     end
 
+    def node_index
+      name.match(%r{(\d+)/\d+$}).captures[0]
+    end
+
     def gitlab_version_info
       @gitlab_version_info ||= Gitlab::VersionInfo.parse(Gitlab::VERSION)
     end

lib/gitlab/ci/config/entry/jobs.rb

@@ -29,6 +29,16 @@ module Gitlab
           # rubocop: disable CodeReuse/ActiveRecord
           def compose!(deps = nil)
             super do
+              @config = @config.map do |name, config|
+                total = config[:parallel]
+                if total
+                  Array.new(total) { { name => config } }
+                    .each_with_index { |build, idx| build["#{name} #{idx + 1}/#{total}".to_sym] = build.delete(name) }
+                else
+                  { name => config }
+                end
+              end.flatten.reduce(:merge)
+
               @config.each do |name, config|
                 node = hidden?(name) ? Entry::Hidden : Entry::Job
 

lib/gitlab/ci/yaml_processor.rb

@@ -50,6 +50,7 @@ module Gitlab
             after_script: job[:after_script],
             environment: job[:environment],
             retry: job[:retry],
+            parallel: job[:parallel],
             start_in: job[:start_in]
           }.compact }
       end

spec/models/ci/build_spec.rb

@@ -1880,6 +1880,7 @@ describe Ci::Build do
         { key: 'CI_COMMIT_BEFORE_SHA', value: build.before_sha, public: true },
         { key: 'CI_COMMIT_REF_NAME', value: build.ref, public: true },
         { key: 'CI_COMMIT_REF_SLUG', value: build.ref_slug, public: true },
+        { key: 'CI_NODE_TOTAL', value: '1', public: true },
         { key: 'CI_BUILD_REF', value: build.sha, public: true },
         { key: 'CI_BUILD_BEFORE_SHA', value: build.before_sha, public: true },
         { key: 'CI_BUILD_REF_NAME', value: build.ref, public: true },
@@ -2341,6 +2342,28 @@ describe Ci::Build do
       end
     end
 
+    context 'when build is parallelized' do
+      let(:total) { 5 }
+      let(:index) { 3 }
+
+      before do
+        build.options[:parallel] = total
+        build.name = "#{build.name} #{index}/#{total}"
+      end
+
+      it 'includes CI_NODE_INDEX' do
+        is_expected.to include(
+          { key: 'CI_NODE_INDEX', value: index.to_s, public: true }
+        )
+      end
+
+      it 'includes correct CI_NODE_TOTAL' do
+        is_expected.to include(
+          { key: 'CI_NODE_TOTAL', value: total.to_s, public: true }
+        )
+      end
+    end
+
     describe 'variables ordering' do
       context 'when variables hierarchy is stubbed' do
         let(:build_pre_var) { { key: 'build', value: 'value', public: true } }
@@ -2447,6 +2470,31 @@ describe Ci::Build do
         end
       end
     end
+
+    describe '#node_index' do
+      subject { build.send(:node_index) }
+      let(:index) { 4 }
+
+      context 'when build has only one index' do
+        before do
+          build.name = "#{build.name} #{index}/5"
+        end
+
+        it 'returns the index' do
+          expect(subject).to eq(index.to_s)
+        end
+      end
+
+      context 'when build has more than one one index' do
+        before do
+          build.name = "test_build 1/3 #{index}/5"
+        end
+
+        it 'returns the last index' do
+          expect(subject).to eq(index.to_s)
+        end
+      end
+    end
   end
 
   describe '#scoped_variables' do