Merge branch 'refactor/ci-config-add-facade' into 'master'

Add new GitLab CI configuration facade class

## What does this MR do?

This MR is a first iteration of major CI configuration refactoring. See #17139 and #15060 for more details.

## What are the relevant issue numbers?

Closes #17139

See merge request !4462

lib/ci/gitlab_ci_yaml_processor.rb

@@ -12,18 +12,14 @@ module Ci
     attr_reader :before_script, :after_script, :image, :services, :path, :cache
 
     def initialize(config, path = nil)
-      @config = YAML.safe_load(config, [Symbol], [], true)
+      @config = Gitlab::Ci::Config.new(config).to_hash
       @path = path
 
-      unless @config.is_a? Hash
-        raise ValidationError, "YAML should be a hash"
-      end
-
-      @config = @config.deep_symbolize_keys
-
       initial_parsing
 
       validate!
+    rescue Gitlab::Ci::Config::Loader::FormatError => e
+      raise ValidationError, e.message
     end
 
     def builds_for_stage_and_ref(stage, ref, tag = false, trigger_request = nil)

lib/gitlab/ci/config.rb

+module Gitlab
+  module Ci
+    class Config
+      class LoaderError < StandardError; end
+
+      def initialize(config)
+        loader = Loader.new(config)
+        @config = loader.load!
+      end
+
+      def to_hash
+        @config
+      end
+    end
+  end
+end

lib/gitlab/ci/config/loader.rb

+module Gitlab
+  module Ci
+    class Config
+      class Loader
+        class FormatError < StandardError; end
+
+        def initialize(config)
+          @config = YAML.safe_load(config, [Symbol], [], true)
+        end
+
+        def valid?
+          @config.is_a?(Hash)
+        end
+
+        def load!
+          unless valid?
+            raise FormatError, 'Invalid configuration format'
+          end
+
+          @config.deep_symbolize_keys
+        end
+      end
+    end
+  end
+end

spec/lib/gitlab/ci/config/loader_spec.rb

+require 'spec_helper'
+
+describe Gitlab::Ci::Config::Loader do
+  let(:loader) { described_class.new(yml) }
+
+  context 'when yaml syntax is correct' do
+    let(:yml) { 'image: ruby:2.2' }
+
+    describe '#valid?' do
+      it 'returns true' do
+        expect(loader.valid?).to be true
+      end
+    end
+
+    describe '#load!' do
+      it 'returns a valid hash' do
+        expect(loader.load!).to eq(image: 'ruby:2.2')
+      end
+    end
+  end
+
+  context 'when yaml syntax is incorrect' do
+    let(:yml) { '// incorrect' }
+
+    describe '#valid?' do
+      it 'returns false' do
+        expect(loader.valid?).to be false
+      end
+    end
+
+    describe '#load!' do
+      it 'raises error' do
+        expect { loader.load! }.to raise_error(
+          Gitlab::Ci::Config::Loader::FormatError,
+          'Invalid configuration format'
+        )
+      end
+    end
+  end
+
+  context 'when yaml config is empty' do
+    let(:yml) { '' }
+
+    describe '#valid?' do
+      it 'returns false' do
+        expect(loader.valid?).to be false
+      end
+    end
+  end
+end

spec/lib/gitlab/ci/config_spec.rb

+require 'spec_helper'
+
+describe Gitlab::Ci::Config do
+  let(:config) do
+    described_class.new(yml)
+  end
+
+  context 'when config is valid' do
+    let(:yml) do
+      <<-EOS
+        image: ruby:2.2
+
+        rspec:
+          script:
+            - gem install rspec
+            - rspec
+      EOS
+    end
+
+    describe '#to_hash' do
+      it 'returns hash created from string' do
+        hash = {
+          image: 'ruby:2.2',
+          rspec: {
+            script: ['gem install rspec',
+                     'rspec']
+          }
+        }
+
+        expect(config.to_hash).to eq hash
+      end
+    end
+
+    context 'when config is invalid' do
+      let(:yml) { '// invalid' }
+
+      describe '.new' do
+        it 'raises error' do
+          expect { config }.to raise_error(
+            Gitlab::Ci::Config::Loader::FormatError,
+            /Invalid configuration format/
+          )
+        end
+      end
+    end
+  end
+end