Assume that unspecified CI config is undefined

We assume that when someone adds a key for the configuration entry, but
does not provide a valid value, which causes entry to be `nil`, then
entry should be considered as the undefined one. We also assume this is
semantically correct, this is also backwards compatible with legacy CI
config processor.

See issue #18775 for more details.

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

@@ -27,7 +27,6 @@ module Gitlab
 
           def create_node(key, factory)
             factory.with(value: @config[key], key: key)
-            factory.undefine! unless @config.has_key?(key)
             factory.create!
           end
 

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

@@ -18,16 +18,20 @@ module Gitlab
             self
           end
 
-          def undefine!
-            @attributes[:value] = @node.dup
-            @node = Node::Undefined
-            self
-          end
-
           def create!
             raise InvalidFactory unless @attributes.has_key?(:value)
 
-            @node.new(@attributes[:value]).tap do |entry|
+            ##
+            # We assume unspecified entry is undefined.
+            # See issue #18775.
+            #
+            if @attributes[:value].nil?
+              node, value = Node::Undefined, @node
+            else
+              node, value = @node, @attributes[:value]
+            end
+
+            node.new(value).tap do |entry|
               entry.description = @attributes[:description]
               entry.key = @attributes[:key]
             end

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

@@ -9,11 +9,7 @@ module Gitlab
           include Validatable
 
           validations do
-            validates :value, variables: true
-          end
-
-          def value
-            @config || self.class.default
+            validates :config, variables: true
           end
 
           def self.default

spec/lib/ci/gitlab_ci_yaml_processor_spec.rb

@@ -551,8 +551,8 @@ module Ci
               config_processor = GitlabCiYamlProcessor.new(config, path)
 
               ##
-              #  TODO, in next version of CI configuration processor this
-              # should be invalid configuration, see #18775 and #15060
+              # When variables config is empty, we asumme this is a correct,
+              # see issue #18775
               #
               expect(config_processor.job_variables(:rspec))
                 .to be_an_instance_of(Array).and be_empty
@@ -1098,14 +1098,14 @@ EOT
         config = YAML.dump({ variables: "test", rspec: { script: "test" } })
         expect do
           GitlabCiYamlProcessor.new(config, path)
-        end.to raise_error(GitlabCiYamlProcessor::ValidationError, "Variables value should be a hash of key value pairs")
+        end.to raise_error(GitlabCiYamlProcessor::ValidationError, "Variables config should be a hash of key value pairs")
       end
 
       it "returns errors if variables is not a map of key-value strings" do
         config = YAML.dump({ variables: { test: false }, rspec: { script: "test" } })
         expect do
           GitlabCiYamlProcessor.new(config, path)
-        end.to raise_error(GitlabCiYamlProcessor::ValidationError, "Variables value should be a hash of key value pairs")
+        end.to raise_error(GitlabCiYamlProcessor::ValidationError, "Variables config should be a hash of key value pairs")
       end
 
       it "returns errors if job when is not on_success, on_failure or always" do

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

@@ -45,11 +45,10 @@ describe Gitlab::Ci::Config::Node::Factory do
       end
     end
 
-    context 'when creating undefined entry' do
-      it 'creates a null entry' do
+    context 'when creating entry with nil value' do
+      it 'creates an undefined entry' do
         entry = factory
           .with(value: nil)
-          .undefine!
           .create!
 
         expect(entry).to be_an_instance_of Gitlab::Ci::Config::Node::Undefined

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

@@ -20,6 +20,7 @@ describe Gitlab::Ci::Config::Node::Global do
   end
 
   context 'when hash is valid' do
+    context 'when all entries defined' do
       let(:hash) do
         { before_script: ['ls', 'pwd'],
           image: 'ruby:2.2',
@@ -103,6 +104,46 @@ describe Gitlab::Ci::Config::Node::Global do
       end
     end
 
+    context 'when most of entires not defined' do
+      let(:hash) { { rspec: {} } }
+      before { global.process! }
+
+      describe '#nodes' do
+        it 'instantizes all nodes' do
+          expect(global.nodes.count).to eq 5
+        end
+
+        it 'contains undefined nodes' do
+          expect(global.nodes.last)
+            .to be_an_instance_of Gitlab::Ci::Config::Node::Undefined
+        end
+      end
+
+      describe '#variables' do
+        it 'returns default value for variables' do
+          expect(global.variables).to eq({})
+        end
+      end
+    end
+
+    ##
+    # When nodes are specified but not defined, we assume that
+    # configuration is valid, and we asume that entry is simply undefined,
+    # despite the fact, that key is present. See issue #18775 for more
+    # details.
+    #
+    context 'when entires specified but not defined' do
+      let(:hash) { { variables: nil } }
+      before { global.process! }
+
+      describe '#variables' do
+        it 'undefined entry returns a default value' do
+          expect(global.variables).to eq({})
+        end
+      end
+    end
+  end
+
   context 'when hash is not valid' do
     before { global.process! }
 

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

@@ -3,9 +3,7 @@ require 'spec_helper'
 describe Gitlab::Ci::Config::Node::Services do
   let(:entry) { described_class.new(config) }
 
-  describe '#process!' do
-    before { entry.process! }
-
+  describe 'validations' do
     context 'when entry config value is correct' do
       let(:config) { ['postgres:9.1', 'mysql:5.5'] }
 

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

@@ -44,24 +44,5 @@ describe Gitlab::Ci::Config::Node::Variables do
         end
       end
     end
-
-    ##
-    # See #18775
-    #
-    context 'when entry value is not defined' do
-      let(:config) { nil }
-
-      describe '#valid?' do
-        it 'is valid' do
-          expect(entry).to be_valid
-        end
-      end
-
-      describe '#values' do
-        it 'returns an empty hash' do
-          expect(entry.value).to eq({})
-        end
-      end
-    end
   end
 end