Add before_script node to CI job entry config

lib/gitlab/ci/config/node/job.rb

@@ -12,20 +12,34 @@ module Gitlab
             validates :config, presence: true
           end
+          node :before_script, Script,
+            description: 'Global before script overridden in this job.'
+
           node :stage, Stage,
             description: 'Pipeline stage this job will be executed into.'
           node :type, Stage,
             description: 'Deprecated: stage this job will be executed into.'
-          helpers :stage, :type
+          helpers :before_script, :stage, :type
           def value
-            @config.merge(stage: stage_value)
+            raise InvalidError unless valid?
+
+            ##
+            # TODO, refactoring step: do not expose internal configuration,
+            # return only hash value without merging it to internal config.
+            #
+            @config.merge(to_hash.compact)
           end
           private
+          def to_hash
+            { before_script: before_script,
+              stage: stage }
+          end
+
           def compose!
             super

spec/lib/ci/gitlab_ci_yaml_processor_spec.rb

@@ -970,7 +970,7 @@ EOT
         config = YAML.dump({ rspec: { script: "test", before_script: [10, "test"] } })
         expect do
           GitlabCiYamlProcessor.new(config, path)
-        end.to raise_error(GitlabCiYamlProcessor::ValidationError, "rspec job: before_script should be an array of strings")
+        end.to raise_error(GitlabCiYamlProcessor::ValidationError, "jobs:rspec:before_script config should be an array of strings")
       end
       it "returns errors if after_script parameter is invalid" do

spec/lib/gitlab/ci/config/node/job_spec.rb

@@ -4,23 +4,15 @@ describe Gitlab::Ci::Config::Node::Job do
   let(:entry) { described_class.new(config, global: global) }
   let(:global) { spy('Global') }
-  describe 'validations' do
   before do
     entry.process!
     entry.validate!
   end
+  describe 'validations' do
     context 'when entry config value is correct' do
       let(:config) { { script: 'rspec' } }
-      describe '#value' do
-        it 'returns key value' do
-          expect(entry.value)
-            .to eq(script: 'rspec',
-                   stage: 'test')
-        end
-      end
-
       describe '#valid?' do
         it 'is valid' do
           expect(entry).to be_valid
@@ -33,7 +25,7 @@ describe Gitlab::Ci::Config::Node::Job do
         let(:config) { ['incorrect'] }
         describe '#errors' do
-          it 'saves errors' do
+          it 'reports error about a config type' do
             expect(entry.errors)
               .to include 'job config should be a hash'
           end
@@ -52,6 +44,32 @@ describe Gitlab::Ci::Config::Node::Job do
     end
   end
+  describe '#value' do
+    context 'when entry is correct' do
+      let(:config) do
+        { before_script: %w[ls pwd],
+          script: 'rspec' }
+      end
+
+      it 'returns correct value' do
+        expect(entry.value)
+          .to eq(before_script: %w[ls pwd],
+                 script: 'rspec',
+                 stage: 'test')
+      end
+    end
+
+    context 'when entry is incorrect' do
+      let(:config) { {} }
+
+      it 'raises error' do
+        expect { entry.value }.to raise_error(
+          Gitlab::Ci::Config::Node::Entry::InvalidError
+        )
+      end
+    end
+  end
+
   describe '#relevant?' do
     it 'is a relevant entry' do
       expect(entry).to be_relevant