prepare 5.2.0 release (#107)

Author: eli-darkly

CHANGELOG.md

@@ -2,6 +2,14 @@
 
 All notable changes to the LaunchDarkly Ruby SDK will be documented in this file. This project adheres to [Semantic Versioning](http://semver.org).
 
+## [5.2.0] - 2018-08-29
+### Added:
+- The new `LDClient` method `variation_detail` allows you to evaluate a feature flag (using the same parameters as you would for `variation`) and receive more information about how the value was calculated. This information is returned in an `EvaluationDetail` object, which contains both the result value and a "reason" object which will tell you, for instance, if the user was individually targeted for the flag or was matched by one of the flag's rules, or if the flag returned the default value due to an error.
+
+### Fixed:
+- Evaluating a prerequisite feature flag did not produce an analytics event if the prerequisite flag was off.
+
+ 
 ## [5.1.0] - 2018-08-27
 ### Added:
 - The new `LDClient` method `all_flags_state()` should be used instead of `all_flags()` if you are passing flag data to the front end for use with the JavaScript SDK. It preserves some flag metadata that the front end requires in order to send analytics events correctly. Versions 2.5.0 and above of the JavaScript SDK are able to use this metadata, but the output of `all_flags_state()` will still work with older versions.

lib/ldclient-rb/evaluation.rb

@@ -2,6 +2,37 @@
 require "semantic"
 
 module LaunchDarkly
+  # An object returned by `LDClient.variation_detail`, combining the result of a flag evaluation with
+  # an explanation of how it was calculated.
+  class EvaluationDetail
+    def initialize(value, variation_index, reason)
+      @value = value
+      @variation_index = variation_index
+      @reason = reason
+    end
+
+    # @return [Object] The result of the flag evaluation. This will be either one of the flag's
+    #   variations or the default value that was passed to the `variation` method.
+    attr_reader :value
+
+    # @return [int|nil] The index of the returned value within the flag's list of variations, e.g.
+    #   0 for the first variation - or `nil` if the default value was returned.
+    attr_reader :variation_index
+
+    # @return [Hash] An object describing the main factor that influenced the flag evaluation value.
+    attr_reader :reason
+
+    # @return [boolean] True if the flag evaluated to the default value rather than to one of its
+    #   variations.
+    def default_value?
+      variation_index.nil?
+    end
+
+    def ==(other)
+      @value == other.value && @variation_index == other.variation_index && @reason == other.reason
+    end
+  end
+
   module Evaluation
     BUILTINS = [:key, :ip, :country, :email, :firstName, :lastName, :avatar, :name, :anonymous]
 
@@ -107,113 +138,103 @@ def self.comparator(converter)
         end
     }
 
-    class EvaluationError < StandardError
+    # Used internally to hold an evaluation result and the events that were generated from prerequisites.
+    EvalResult = Struct.new(:detail, :events)
+
+    def error_result(errorKind, value = nil)
+      EvaluationDetail.new(value, nil, { kind: 'ERROR', errorKind: errorKind })
     end
 
-    # Evaluates a feature flag, returning a hash containing the evaluation result and any events
-    # generated during prerequisite evaluation. Raises EvaluationError if the flag is not well-formed
-    # Will return nil, but not raise an exception, indicating that the rules (including fallthrough) did not match
-    # In that case, the caller should return the default value.
+    # Evaluates a feature flag and returns an EvalResult. The result.value will be nil if the flag returns
+    # the default value. Error conditions produce a result with an error reason, not an exception.
     def evaluate(flag, user, store, logger)
-      if flag.nil?
-        raise EvaluationError, "Flag does not exist"
-      end
-
       if user.nil? || user[:key].nil?
-        raise EvaluationError, "Invalid user"
+        return EvalResult.new(error_result('USER_NOT_SPECIFIED'), [])
       end
 
       events = []
+      detail = eval_internal(flag, user, store, events, logger)
+      return EvalResult.new(detail, events)
+    end
+
+    def eval_internal(flag, user, store, events, logger)
+      if !flag[:on]
+        return get_off_value(flag, { kind: 'OFF' }, logger)
+      end
 
-      if flag[:on]
-        res = eval_internal(flag, user, store, events, logger)
-        if !res.nil?
-          res[:events] = events
-          return res
+      prereq_failure_reason = check_prerequisites(flag, user, store, events, logger)
+      if !prereq_failure_reason.nil?
+        return get_off_value(flag, prereq_failure_reason, logger)
+      end
+
+      # Check user target matches
+      (flag[:targets] || []).each do |target|
+        (target[:values] || []).each do |value|
+          if value == user[:key]
+            return get_variation(flag, target[:variation], { kind: 'TARGET_MATCH' }, logger)
+          end
+        end
+      end
+    
+      # Check custom rules
+      rules = flag[:rules] || []
+      rules.each_index do |i|
+        rule = rules[i]
+        if rule_match_user(rule, user, store)
+          return get_value_for_variation_or_rollout(flag, rule, user,
+            { kind: 'RULE_MATCH', ruleIndex: i, ruleId: rule[:id] }, logger)
         end
       end
 
-      offVariation = flag[:offVariation]
-      if !offVariation.nil? && offVariation < flag[:variations].length
-        value = flag[:variations][offVariation]
-        return { variation: offVariation, value: value, events: events }
+      # Check the fallthrough rule
+      if !flag[:fallthrough].nil?
+        return get_value_for_variation_or_rollout(flag, flag[:fallthrough], user,
+          { kind: 'FALLTHROUGH' }, logger)
       end
 
-      { variation: nil, value: nil, events: events }
+      return EvaluationDetail.new(nil, nil, { kind: 'FALLTHROUGH' })
     end
 
-    def eval_internal(flag, user, store, events, logger)
-      failed_prereq = false
-      # Evaluate prerequisites, if any
+    def check_prerequisites(flag, user, store, events, logger)
       (flag[:prerequisites] || []).each do |prerequisite|
-        prereq_flag = store.get(FEATURES, prerequisite[:key])
+        prereq_ok = true
+        prereq_key = prerequisite[:key]
+        prereq_flag = store.get(FEATURES, prereq_key)
 
-        if prereq_flag.nil? || !prereq_flag[:on]
-          failed_prereq = true
+        if prereq_flag.nil?
+          logger.error { "[LDClient] Could not retrieve prerequisite flag \"#{prereq_key}\" when evaluating \"#{flag[:key]}\"" }
+          prereq_ok = false
         else
           begin
             prereq_res = eval_internal(prereq_flag, user, store, events, logger)
+            # Note that if the prerequisite flag is off, we don't consider it a match no matter what its
+            # off variation was. But we still need to evaluate it in order to generate an event.
+            if !prereq_flag[:on] || prereq_res.variation_index != prerequisite[:variation]
+              prereq_ok = false
+            end
             event = {
               kind: "feature",
-              key: prereq_flag[:key],
-              variation: prereq_res.nil? ? nil : prereq_res[:variation],
-              value: prereq_res.nil? ? nil : prereq_res[:value],
+              key: prereq_key,
+              variation: prereq_res.variation_index,
+              value: prereq_res.value,
               version: prereq_flag[:version],
               prereqOf: flag[:key],
               trackEvents: prereq_flag[:trackEvents],
               debugEventsUntilDate: prereq_flag[:debugEventsUntilDate]
             }
             events.push(event)
-            if prereq_res.nil? || prereq_res[:variation] != prerequisite[:variation]
-              failed_prereq = true
-            end
           rescue => exn
-            logger.error { "[LDClient] Error evaluating prerequisite: #{exn.inspect}" }
-            failed_prereq = true
+            Util.log_exception(logger, "Error evaluating prerequisite flag \"#{prereq_key}\" for flag \"{flag[:key]}\"", exn)
+            prereq_ok = false
           end
         end
-      end
-
-      if failed_prereq
-        return nil
-      end
-      # The prerequisites were satisfied.
-      # Now walk through the evaluation steps and get the correct
-      # variation index
-      eval_rules(flag, user, store)
-    end
-
-    def eval_rules(flag, user, store)
-      # Check user target matches
-      (flag[:targets] || []).each do |target|
-        (target[:values] || []).each do |value|
-          if value == user[:key]
-            return { variation: target[:variation], value: get_variation(flag, target[:variation]) }
-          end
+        if !prereq_ok
+          return { kind: 'PREREQUISITE_FAILED', prerequisiteKey: prereq_key }
         end
       end
-    
-      # Check custom rules
-      (flag[:rules] || []).each do |rule|
-        return variation_for_user(rule, user, flag) if rule_match_user(rule, user, store)
-      end
-
-      # Check the fallthrough rule
-      if !flag[:fallthrough].nil?
-        return variation_for_user(flag[:fallthrough], user, flag)
-      end
-
-      # Not even the fallthrough matched-- return the off variation or default
       nil
     end
 
-    def get_variation(flag, index)
-      if index >= flag[:variations].length
-        raise EvaluationError, "Invalid variation index"
-      end
-      flag[:variations][index]
-    end
-
     def rule_match_user(rule, user, store)
       return false if !rule[:clauses]
 
@@ -242,9 +263,8 @@ def clause_match_user_no_segments(clause, user)
       return false if val.nil?
 
       op = OPERATORS[clause[:op].to_sym]
-
       if op.nil?
-        raise EvaluationError, "Unsupported operator #{clause[:op]} in evaluation"
+        return false
       end
 
       if val.is_a? Enumerable
@@ -257,9 +277,9 @@ def clause_match_user_no_segments(clause, user)
       maybe_negate(clause, match_any(op, val, clause[:values]))
     end
 
-    def variation_for_user(rule, user, flag)
+    def variation_index_for_user(flag, rule, user)
       if !rule[:variation].nil? # fixed variation
-        return { variation: rule[:variation], value: get_variation(flag, rule[:variation]) }
+        return rule[:variation]
       elsif !rule[:rollout].nil? # percentage rollout
         rollout = rule[:rollout]
         bucket_by = rollout[:bucketBy].nil? ? "key" : rollout[:bucketBy]
@@ -268,12 +288,12 @@ def variation_for_user(rule, user, flag)
         rollout[:variations].each do |variate|
           sum += variate[:weight].to_f / 100000.0
           if bucket < sum
-            return { variation: variate[:variation], value: get_variation(flag, variate[:variation]) }
+            return variate[:variation]
           end
         end
         nil
       else # the rule isn't well-formed
-        raise EvaluationError, "Rule does not define a variation or rollout"
+        nil
       end
     end
 
@@ -350,5 +370,31 @@ def match_any(op, value, values)
       end
       return false
     end
+
+    private
+
+    def get_variation(flag, index, reason, logger)
+      if index < 0 || index >= flag[:variations].length
+        logger.error("[LDClient] Data inconsistency in feature flag \"#{flag[:key]}\": invalid variation index")
+        return error_result('MALFORMED_FLAG')
+      end
+      EvaluationDetail.new(flag[:variations][index], index, reason)
+    end
+
+    def get_off_value(flag, reason, logger)
+      if flag[:offVariation].nil?  # off variation unspecified - return default value
+        return EvaluationDetail.new(nil, nil, reason)
+      end
+      get_variation(flag, flag[:offVariation], reason, logger)
+    end
+
+    def get_value_for_variation_or_rollout(flag, vr, user, reason, logger)
+      index = variation_index_for_user(flag, vr, user)
+      if index.nil?
+        logger.error("[LDClient] Data inconsistency in feature flag \"#{flag[:key]}\": variation/rollout object with no variation or rollout")
+        return error_result('MALFORMED_FLAG')
+      end
+      return get_variation(flag, index, reason, logger)
+    end
   end
 end

lib/ldclient-rb/events.rb

@@ -363,6 +363,7 @@ def make_output_event(event)
         else
           out[:userKey] = event[:user].nil? ? nil : event[:user][:key]
         end
+        out[:reason] = event[:reason] if !event[:reason].nil?
         out
       when "identify"
         {

lib/ldclient-rb/flags_state.rb

@@ -15,12 +15,13 @@ def initialize(valid)
     end
 
     # Used internally to build the state map.
-    def add_flag(flag, value, variation)
+    def add_flag(flag, value, variation, reason = nil)
       key = flag[:key]
       @flag_values[key] = value
       meta = { version: flag[:version], trackEvents: flag[:trackEvents] }
       meta[:variation] = variation if !variation.nil?
       meta[:debugEventsUntilDate] = flag[:debugEventsUntilDate] if flag[:debugEventsUntilDate]
+      meta[:reason] = reason if !reason.nil?
       @flag_metadata[key] = meta
     end