Extract internal attributes validator for CI entry

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

@@ -10,13 +10,7 @@ module Gitlab
           validations do
             validates :config, key: true
-
-            validate do |entry|
-              unless entry.global
-                raise Entry::InvalidError,
-                  'This entry needs reference to global configuration'
-              end
-            end
+            validates :global, required_attribute: true
           end
           def self.default

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

@@ -33,6 +33,15 @@ module Gitlab
             end
           end
+          class RequiredAttributeValidator < ActiveModel::EachValidator
+            def validate_each(record, attribute, value)
+              if value.nil?
+                raise Entry::InvalidError,
+                  "Entry needs #{attribute} attribute set internally."
+              end
+            end
+          end
+
           class KeyValidator < ActiveModel::EachValidator
             include LegacyValidationHelpers

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

@@ -27,8 +27,10 @@ describe Gitlab::Ci::Config::Node::Stage do
           let(:entry) { described_class.new(config) }
           it 'raises error' do
-            expect { entry }
-              .to raise_error Gitlab::Ci::Config::Node::Entry::InvalidError
+            expect { entry }.to raise_error(
+              Gitlab::Ci::Config::Node::Entry::InvalidError,
+              /Entry needs global attribute set internally./
+            )
           end
         end