Add Kubernetes option to environment CI config

Introduces a new CI configuration option that allows
specifying the Kubernetes namespace that an environment
will be deployed to. This option does not currently
have any effect on deployments, deploying to the
specified namespace will be added as part of
https://gitlab.com/gitlab-org/gitlab/issues/27630

Example usage:

environment:
  name: production
  url: https://production.example.com
  kubernetes:
    namespace: production

changelogs/unreleased/27630-specify-kubernetes-namespace-in-ci-template.yml

+---
+title: Allow specifying Kubernetes namespace for an environment in gitlab-ci.yml
+merge_request: 20270
+author:
+type: added

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

@@ -8,9 +8,11 @@ module Gitlab
         # Entry that represents an environment.
         #
         class Environment < ::Gitlab::Config::Entry::Node
-          include ::Gitlab::Config::Entry::Validatable
+          include ::Gitlab::Config::Entry::Configurable
 
-          ALLOWED_KEYS = %i[name url action on_stop].freeze
+          ALLOWED_KEYS = %i[name url action on_stop kubernetes].freeze
+
+          entry :kubernetes, Entry::Kubernetes, description: 'Kubernetes deployment configuration.'
 
           validations do
             validate do
@@ -46,6 +48,7 @@ module Gitlab
                         allow_nil: true
 
               validates :on_stop, type: String, allow_nil: true
+              validates :kubernetes, type: Hash, allow_nil: true
             end
           end
 
@@ -73,6 +76,10 @@ module Gitlab
             value[:on_stop]
           end
 
+          def kubernetes
+            value[:kubernetes]
+          end
+
           def value
             case @config
             when String then { name: @config, action: 'start' }
@@ -80,6 +87,10 @@ module Gitlab
             else {}
             end
           end
+
+          def skip_config_hash_validation?
+            true
+          end
         end
       end
     end

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

+# frozen_string_literal: true
+
+module Gitlab
+  module Ci
+    class Config
+      module Entry
+        class Kubernetes < ::Gitlab::Config::Entry::Node
+          include ::Gitlab::Config::Entry::Validatable
+          include ::Gitlab::Config::Entry::Attributable
+
+          ALLOWED_KEYS = %i[namespace].freeze
+
+          attributes ALLOWED_KEYS
+
+          validations do
+            validates :config, type: Hash
+            validates :config, allowed_keys: ALLOWED_KEYS
+
+            validates :namespace, type: String, presence: true
+          end
+        end
+      end
+    end
+  end
+end

spec/lib/gitlab/ci/config/entry/environment_spec.rb

@@ -241,4 +241,28 @@ describe Gitlab::Ci::Config::Entry::Environment do
       end
     end
   end
+
+  describe 'kubernetes' do
+    let(:config) do
+      { name: 'production', kubernetes: kubernetes_config }
+    end
+
+    context 'is a string' do
+      let(:kubernetes_config) { 'production' }
+
+      it { expect(entry).not_to be_valid }
+    end
+
+    context 'is a hash' do
+      let(:kubernetes_config) { Hash(namespace: 'production') }
+
+      it { expect(entry).to be_valid }
+    end
+
+    context 'is nil' do
+      let(:kubernetes_config) { nil }
+
+      it { expect(entry).to be_valid }
+    end
+  end
 end

spec/lib/gitlab/ci/config/entry/kubernetes_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::Ci::Config::Entry::Kubernetes do
+  subject { described_class.new(config) }
+
+  describe 'attributes' do
+    it { is_expected.to respond_to(:namespace) }
+    it { is_expected.to respond_to(:has_namespace?) }
+  end
+
+  describe 'validations' do
+    describe 'config' do
+      context 'is a hash containing known keys' do
+        let(:config) { Hash(namespace: 'namespace') }
+
+        it { is_expected.to be_valid }
+      end
+
+      context 'is a hash containing an unknown key' do
+        let(:config) { Hash(unknown: 'attribute') }
+
+        it { is_expected.not_to be_valid }
+      end
+
+      context 'is a string' do
+        let(:config) { 'config' }
+
+        it { is_expected.not_to be_valid }
+      end
+    end
+
+    describe 'namespace' do
+      let(:config) { Hash(namespace: namespace) }
+
+      context 'is a string' do
+        let(:namespace) { 'namespace' }
+
+        it { is_expected.to be_valid }
+      end
+
+      context 'is a hash' do
+        let(:namespace) { Hash(key: 'namespace') }
+
+        it { is_expected.not_to be_valid }
+      end
+
+      context 'is not present' do
+        let(:namespace) { '' }
+
+        it { is_expected.not_to be_valid }
+      end
+    end
+  end
+end

spec/services/ci/create_pipeline_service_spec.rb

@@ -801,6 +801,32 @@ describe Ci::CreatePipelineService do
       end
     end
 
+    context 'environment with Kubernetes configuration' do
+      let(:kubernetes_namespace) { 'custom-namespace' }
+
+      before do
+        config = YAML.dump(
+          deploy: {
+            environment: {
+              name: "environment-name",
+              kubernetes: { namespace: kubernetes_namespace }
+            },
+            script: 'ls'
+          }
+        )
+
+        stub_ci_pipeline_yaml_file(config)
+      end
+
+      it 'stores the requested namespace' do
+        result = execute_service
+        build = result.builds.first
+
+        expect(result).to be_persisted
+        expect(build.options.dig(:environment, :kubernetes, :namespace)).to eq(kubernetes_namespace)
+      end
+    end
+
     context 'when environment with invalid name' do
       before do
         config = YAML.dump(deploy: { environment: { name: 'name,with,commas' }, script: 'ls' })