Support recursive `extends:` in `.gitlab-ci.yml`

lib/gitlab/ci/config/extendable.rb

-module Gitlab
-  module Ci
-    class Config
-      class Extendable
-        include Enumerable
-
-        ExtensionError = Class.new(StandardError)
-
-        def initialize(hash)
-          @hash = hash
-        end
-
-        def each
-          @hash.each_pair do |key, value|
-            next unless value.key?(:extends)
-
-            yield key, value.fetch(:extends).to_sym, value
-          end
-        end
-
-        def extend!
-          @hash.tap do
-            each do |key, extends, value|
-              @hash[key] = @hash.fetch(extends).deep_merge(value)
-            end
-          end
-        end
-      end
-    end
-  end
-end

lib/gitlab/ci/config/extendable/collection.rb

+module Gitlab
+  module Ci
+    class Config
+      module Extendable
+        class Collection
+          include Enumerable
+
+          ExtensionError = Class.new(StandardError)
+
+          def initialize(hash, context = hash)
+            @hash = hash
+            @context = context
+          end
+
+          def each
+            @hash.each_pair do |key, value|
+              next unless value.key?(:extends)
+
+              yield Extendable::Entry.new(key, value, @context)
+            end
+          end
+
+          def extend!
+            each do |entry|
+              raise ExtensionError unless entry.valid?
+
+              @hash[entry.key] = entry.extend!
+            end
+          end
+        end
+      end
+    end
+  end
+end

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

+module Gitlab
+  module Ci
+    class Config
+      module Extendable
+        class Entry
+          attr_reader :key
+
+          def initialize(key, value, context, parent = nil)
+            @key = key
+            @value = value
+            @context = context
+            @parent = parent
+          end
+
+          def valid?
+            true
+          end
+
+          # def circular_dependency?
+          #   @extends.to_s == @key.to_s
+          # end
+
+          def base
+            Extendable::Entry
+              .new(extends, @context.fetch(extends), @context, self)
+              .extend!
+          end
+
+          def extensible?
+            @value.key?(:extends)
+          end
+
+          def extends
+            @value.fetch(:extends).to_sym
+          end
+
+          def extend!
+            if extensible?
+              original = @value.dup
+              parent = base.dup
+
+              @value.clear.deep_merge!(parent).deep_merge!(original)
+            else
+              @value.to_h
+            end
+          end
+        end
+      end
+    end
+  end
+end

spec/lib/gitlab/ci/config/extendable_spec.rb → spec/lib/gitlab/ci/config/extendable/collection_spec.rb

 require 'fast_spec_helper'
 
-describe Gitlab::Ci::Config::Extendable do
+describe Gitlab::Ci::Config::Extendable::Collection do
   subject { described_class.new(hash) }
 
   describe '#each' do
@@ -14,12 +14,19 @@ describe Gitlab::Ci::Config::Extendable do
       end
 
       it 'yields the test hash' do
-        expect { |b| subject.each(&b) }
-          .to yield_with_args(:test, :something, test)
+        expect { |b| subject.each(&b) }.to yield_control
       end
     end
 
-    pending 'when not extending using a hash'
+    context 'when not extending using a hash' do
+      let(:hash) do
+        { something: { extends: [1], script: 'ls' } }
+      end
+
+      it 'yields invalid extends as well' do
+        expect { |b| subject.each(&b) }.to yield_control
+      end
+    end
   end
 
   describe '#extend!' do
@@ -30,6 +37,7 @@ describe Gitlab::Ci::Config::Extendable do
             script: 'deploy',
             only: { variables: %w[$SOMETHING] }
           },
+
           test: {
             extends: 'something',
             script: 'ls',
@@ -38,12 +46,13 @@ describe Gitlab::Ci::Config::Extendable do
         }
       end
 
-      it 'extends a hash with reverse merge' do
+      it 'extends a hash with a deep reverse merge' do
         expect(subject.extend!).to eq(
           something: {
             script: 'deploy',
             only: { variables: %w[$SOMETHING] }
           },
+
           test: {
             extends: 'something',
             script: 'ls',
@@ -56,8 +65,58 @@ describe Gitlab::Ci::Config::Extendable do
       end
     end
 
-    pending 'when a hash recursive extensions'
+    context 'when a hash uses recursive extensions' do
+      let(:hash) do
+        {
+          test: {
+            extends: 'something',
+            script: 'ls',
+            only: { refs: %w[master] }
+          },
+
+          something: {
+            extends: '.first',
+            script: 'deploy',
+            only: { variables: %w[$SOMETHING] }
+          },
+
+          '.first': {
+            script: 'run',
+            only: { kubernetes: 'active' }
+          }
+        }
+      end
+
+      it 'extends a hash with a deep reverse merge' do
+        expect(subject.extend!).to eq(
+          '.first': {
+            script: 'run',
+            only: { kubernetes: 'active' }
+          },
+
+          something: {
+            extends: '.first',
+            script: 'deploy',
+            only: {
+              kubernetes: 'active',
+              variables: %w[$SOMETHING]
+            }
+          },
+
+          test: {
+            extends: 'something',
+            script: 'ls',
+            only: {
+              refs: %w[master],
+              variables: %w[$SOMETHING],
+              kubernetes: 'active'
+            }
+          }
+        )
+      end
+    end
 
     pending 'when invalid `extends` is specified'
+    pending 'when circular dependecy has been detected'
   end
 end