Evaluate the variables for runner tags section

lib/gitlab/ci/pipeline/seed/build.rb

@@ -67,6 +67,7 @@ module Gitlab
               .deep_merge(rules_attributes)
               .deep_merge(allow_failure_criteria_attributes)
               .deep_merge(@cache.cache_attributes)
+              .deep_merge(runner_tags)
           end
 
           def bridge?
@@ -202,6 +203,16 @@ module Gitlab
             end
           end
 
+          def runner_tags
+            { tag_list: evaluate_runner_tags }.compact
+          end
+
+          def evaluate_runner_tags
+            @seed_attributes[:tag_list]&.map do |tag|
+              ExpandVariables.expand_existing(tag, evaluate_context.variables)
+            end
+          end
+
           # If a job uses `allow_failure:exit_codes` and `rules:allow_failure`
           # we need to prevent the exit codes from being persisted because they
           # would break the behavior defined by `rules:allow_failure`.

spec/lib/gitlab/ci/pipeline/seed/build_spec.rb

@@ -90,6 +90,20 @@ RSpec.describe Gitlab::Ci::Pipeline::Seed::Build do
       end
     end
 
+    context 'with job:tags' do
+      let(:attributes) do
+        {
+          name: 'rspec',
+          ref: 'master',
+          job_variables: [{ key: 'VARIABLE', value: 'value', public: true }],
+          tag_list: ['static-tag', '$VARIABLE', '$NO_VARIABLE']
+        }
+      end
+
+      it { is_expected.to include(tag_list: ['static-tag', 'value', '$NO_VARIABLE']) }
+      it { is_expected.to include(yaml_variables: [{ key: 'VARIABLE', value: 'value', public: true }]) }
+    end
+
     context 'with cache:key' do
       let(:attributes) do
         {

spec/services/ci/create_pipeline_service/evaluate_runner_tags_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Ci::CreatePipelineService do
+  let_it_be(:group)          { create(:group, :private) }
+  let_it_be(:group_variable) { create(:ci_group_variable, group: group, key: 'RUNNER_TAG', value: 'group')}
+  let_it_be(:project)        { create(:project, :repository, group: group) }
+  let_it_be(:user)           { create(:user) }
+
+  let(:service)  { described_class.new(project, user, ref: 'master') }
+  let(:pipeline) { service.execute(:push) }
+  let(:job)      { pipeline.builds.find_by(name: 'job') }
+
+  before do
+    project.add_developer(user)
+    stub_ci_pipeline_yaml_file config
+  end
+
+  context 'when the variable is set' do
+    let(:config) do
+      <<~EOS
+        variables:
+          KUBERNETES_RUNNER: kubernetes
+
+        job:
+          tags:
+            - docker
+            - $KUBERNETES_RUNNER
+          script:
+            - echo "Hello runner selector feature"
+      EOS
+    end
+
+    it 'uses the evaluated variable' do
+      expect(pipeline).to be_created_successfully
+      expect(job.tags.pluck(:name)).to match_array(%w[docker kubernetes])
+    end
+  end
+
+  context 'when the tag is composed by two variables' do
+    let(:config) do
+      <<~EOS
+        variables:
+          CLOUD_PROVIDER: aws
+          KUBERNETES_RUNNER: kubernetes
+          ENVIRONMENT_NAME: prod
+
+        job:
+          tags:
+            - docker
+            - $CLOUD_PROVIDER-$KUBERNETES_RUNNER-$ENVIRONMENT_NAME
+          script:
+            - echo "Hello runner selector feature"
+      EOS
+    end
+
+    it 'uses the evaluated variables' do
+      expect(pipeline).to be_created_successfully
+      expect(job.tags.pluck(:name)).to match_array(%w[docker aws-kubernetes-prod])
+    end
+  end
+
+  context 'when the variable is not set' do
+    let(:config) do
+      <<~EOS
+        job:
+          tags:
+            - docker
+            - $KUBERNETES_RUNNER
+          script:
+            - echo "Hello runner selector feature"
+      EOS
+    end
+
+    it 'uses the variable as a regular string' do
+      expect(pipeline).to be_created_successfully
+      expect(job.tags.pluck(:name)).to match_array(%w[docker $KUBERNETES_RUNNER])
+    end
+  end
+
+  context 'when the tag uses group variables' do
+    let(:config) do
+      <<~EOS
+        job:
+          tags:
+            - docker
+            - $RUNNER_TAG
+          script:
+            - echo "Hello runner selector feature"
+      EOS
+    end
+
+    it 'uses the evaluated variables' do
+      expect(pipeline).to be_created_successfully
+      expect(job.tags.pluck(:name)).to match_array(%w[docker group])
+    end
+  end
+
+  context 'when the tag has the same variable name defined for both group and project' do
+    let_it_be(:project_variable) { create(:ci_variable, project: project, key: 'RUNNER_TAG', value: 'project') }
+
+    let(:config) do
+      <<~EOS
+        variables:
+          RUNNER_TAG: pipeline
+        job:
+          tags:
+            - docker
+            - $RUNNER_TAG
+          script:
+            - echo "Hello runner selector feature"
+      EOS
+    end
+
+    it 'uses the project variable instead of group due to variable precedence' do
+      expect(pipeline).to be_created_successfully
+      expect(job.tags.pluck(:name)).to match_array(%w[docker project])
+    end
+  end
+
+  context 'with parallel:matrix config' do
+    let(:tags) { pipeline.builds.map(&:tags).flatten.pluck(:name) }
+
+    let(:config) do
+      <<~EOS
+        job:
+          parallel:
+            matrix:
+              - PROVIDER: [aws, gcp]
+                STACK: [monitoring, backup, app]
+          tags:
+            - ${PROVIDER}-${STACK}
+          script:
+            - echo "Hello runner selector feature"
+      EOS
+    end
+
+    it 'uses the evaluated variables' do
+      expect(pipeline).to be_created_successfully
+      expect(tags).to match_array(%w[aws-monitoring aws-backup aws-app gcp-monitoring gcp-backup gcp-app])
+    end
+  end
+end