Add IS_SET and IS_NOT_SET segment operators (#20)

* Add IS_SET and IS_NOT_SET segment operators

* Simplify logic and disable rubocop

* Fix rubocop

* make logic clearer

* Update test wording

Author: matthewelwell

lib/flagsmith/engine/segments/constants.rb

@@ -22,6 +22,8 @@ module Constants
         NOT_EQUAL = 'NOT_EQUAL'
         REGEX = 'REGEX'
         PERCENTAGE_SPLIT = 'PERCENTAGE_SPLIT'
+        IS_SET = 'IS_SET'
+        IS_NOT_SET = 'IS_NOT_SET'
         MODULO = 'MODULO'
 
         CONDITION_OPERATORS = [

lib/flagsmith/engine/segments/evaluator.rb

@@ -58,10 +58,22 @@ def traits_match_segment_condition(identity_traits, condition, segment_id, ident
 
           trait = identity_traits.find { |t| t.key.to_s == condition.property }
 
-          return condition.match_trait_value?(trait.value) if trait
+          if [IS_SET, IS_NOT_SET].include?(condition.operator)
+            return handle_trait_existence_conditions(trait, condition.operator)
+          end
+
+          return condition.match_trait_value?(trait.trait_value) if trait
 
           false
         end
+
+        private
+
+        def handle_trait_existence_conditions(matching_trait, operator)
+          return operator == IS_NOT_SET if matching_trait.nil?
+
+          operator == IS_SET
+        end
       end
     end
   end

spec/engine/unit/segments/evaluator_spec.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+# list of test cases containing: operator, property, value, traits (list of dicts), expected_result
+TEST_CASES = [
+    ['IS_SET', 'foo', nil, {}, false],
+    ['IS_SET', 'foo', nil, {'foo': 'bar'}, true],
+    ['IS_NOT_SET', 'foo', nil, {}, true],
+    ['IS_NOT_SET', 'foo', nil, {'foo': 'bar'}, false],
+]
+
+RSpec.describe Flagsmith::Engine::Segments::Evaluator do
+  subject { Class.new { extend Flagsmith::Engine::Segments::Evaluator } }
+
+  TEST_CASES.each do |(operator, property, value, traits, expected_result)|
+    it "traits: #{traits} #traits_match_segment_condition(#{operator}, #{property}, #{value || 'No value'}) should be #{expected_result}" do
+      condition = Flagsmith::Engine::Segments::Condition.new(
+        operator: operator, property: property, value: value
+      )
+      trait_models = traits.map { 
+        |k,v| Flagsmith::Engine::Identities::Trait.new(trait_key: k, trait_value: v) 
+      }
+
+      expect(subject.traits_match_segment_condition(
+        trait_models, condition, 1, 1)).to eq(expected_result)
+    end
+  end
+end

spec/sdk/flagsmith_spec.rb

@@ -110,7 +110,7 @@
   end
 
   describe '#get_identity_segments' do
-    it 'returns an empty list given an identity with no traits' do
+    it 'returns an empty list given an identity which matches no segment conditions' do
       polling_manager = Flagsmith::EnvironmentDataPollingManager.new(subject, 60)
       subject.update_environment()
       expect(subject.get_identity_segments("identifier")).to eq([])