Implement complex only/except policy CI/CD config

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

@@ -3,7 +3,7 @@ module Gitlab
     class Config
       module Entry
         ##
-        # Entry that represents a trigger policy for the job.
+        # Entry that represents an only/except trigger policy for the job.
         #
         class Policy < Simplifiable
           strategy :RefsPolicy, if: -> (config) { config.is_a?(Array) }
@@ -23,9 +23,25 @@ module Gitlab
 
           class ExpressionsPolicy < Entry::Node
             include Entry::Validatable
+            include Entry::Attributable
+
+            attributes :refs, :expressions
 
             validations do
-              validates :config, type: Hash
+              validates :config, presence: true
+              validates :config, allowed_keys: %i[refs expressions]
+
+              with_options allow_nil: true do
+                validates :refs, array_of_strings_or_regexps: true
+                validates :expressions, type: Array
+                validates :expressions, presence: true
+              end
+            end
+          end
+
+          class UnknownStrategy < Entry::Node
+            def errors
+              ['policy has to be either an array of conditions or a hash']
             end
           end
         end

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

@@ -10,7 +10,7 @@ module Gitlab
               variant.condition.call(config)
             end
 
-            entry = self.class.const_get(strategy.name)
+            entry = self.class.entry_class(strategy)
 
             super(entry.new(config, metadata))
           end
@@ -22,7 +22,15 @@ module Gitlab
           end
 
           def self.strategies
-            @strategies || []
+            @strategies.to_a
+          end
+
+          def self.entry_class(strategy)
+            if strategy.present?
+              self.const_get(strategy.name)
+            else
+              self::UnknownStrategy
+            end
           end
         end
       end

spec/lib/gitlab/ci/config/entry/policy_spec.rb

@@ -57,5 +57,31 @@ describe Gitlab::Ci::Config::Entry::Policy do
   end
 
   context 'when using complex policy' do
+    context 'when it is an empty hash' do
+      let(:config) { { } }
+
+      it 'reports an error about configuration not being present' do
+        expect(entry.errors).to include /can't be blank/
+      end
+    end
+
+    context 'when it contains unknown keys' do
+      let(:config) { { refs: ['something'], invalid: 'master' } }
+
+      it 'is not valid entry' do
+        expect(entry).not_to be_valid
+        expect(entry.errors)
+          .to include /policy config contains unknown keys: invalid/
+      end
+    end
+  end
+
+  context 'when policy strategy does not match' do
+    let(:config) { 'string strategy' }
+
+    it 'returns information about errors' do
+      expect(entry.errors)
+        .to include 'policy has to be either an array of conditions or a hash'
+    end
   end
 end