feat(Flag Dependency): Evaluate flags that depend on other flags (#240)

Co-authored-by: linear-code[bot] <222613912+linear-code[bot]@users.noreply.github.com>
Co-authored-by: Evandro Myller <22429+emyller@users.noreply.github.com>
Co-authored-by: Evandro Myller <evandro.myller@flagsmith.com>
Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: 3 people

.github/workflows/sdk-spec.yml

@@ -11,7 +11,8 @@ permissions:
 jobs:
   sdk-spec:
     # Keep the ref in `uses:` and `spec-ref` in sync.
-    uses: Flagsmith/sdk-spec/.github/workflows/run-spec.yml@v0.3.0
+    uses: Flagsmith/sdk-spec/.github/workflows/run-spec.yml@v0.7.0
     with:
-      spec-ref: v0.3.0
+      spec-ref: v0.7.0
       language: java
+      tags: core or local-evaluation

.gitmodules

@@ -1,7 +1,7 @@
 [submodule "src/test/java/com/flagsmith/flagengine/enginetestdata"]
 	path = src/test/java/com/flagsmith/flagengine/enginetestdata
 	url = git@github.com:Flagsmith/engine-test-data.git
-	branch = v3.7.0
+	branch = v3.11.0
 [submodule "third-party/codspeed-jvm"]
 	path = third-party/codspeed-jvm
 	url = https://github.com/CodSpeedHQ/codspeed-jvm.git

sdk-spec/Steps.java

@@ -1,4 +1,5 @@
 import com.flagsmith.FlagsmithClient;
+import com.flagsmith.config.FlagsmithConfig;
 import com.flagsmith.exceptions.FlagsmithClientError;
 import com.flagsmith.models.BaseFlag;
 import com.flagsmith.models.Flags;
@@ -35,6 +36,17 @@ static FlagsmithClient createClient(String environmentKey, String apiUrl) {
     return FlagsmithClient.newBuilder().setApiKey(environmentKey).withApiUrl(apiUrl).build();
   }
 
+  // Create the SDK client with local evaluation
+  static FlagsmithClient createClientWithLocalEvaluation(String environmentKey, String apiUrl) {
+    return FlagsmithClient.newBuilder()
+        .setApiKey(environmentKey)
+        .withConfiguration(FlagsmithConfig.newBuilder()
+            .baseUri(apiUrl)
+            .withLocalEvaluation(true)
+            .build())
+        .build();
+  }
+
   // When the application gets the environment flags
   static List<SpecFlag> getEnvironmentFlags(FlagsmithClient flagsmith)
       throws FlagsmithClientError {

src/main/java/com/flagsmith/FlagsmithClient.java

@@ -9,6 +9,8 @@
 import com.flagsmith.flagengine.Engine;
 import com.flagsmith.flagengine.EvaluationContext;
 import com.flagsmith.flagengine.EvaluationResult;
+import com.flagsmith.flagengine.SegmentRule;
+import com.flagsmith.flagengine.Segments;
 import com.flagsmith.interfaces.FlagsmithCache;
 import com.flagsmith.interfaces.FlagsmithSdk;
 import com.flagsmith.mappers.EngineMappers;
@@ -30,9 +32,11 @@
 import java.util.stream.Collectors;
 import lombok.AccessLevel;
 import lombok.Data;
+import lombok.EqualsAndHashCode;
 import lombok.Getter;
 import lombok.NonNull;
 import lombok.Setter;
+import lombok.ToString;
 import org.apache.commons.lang3.StringUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -43,9 +47,17 @@
 @Data
 public class FlagsmithClient {
 
+  private static final List<String> IDENTITY_FREE_PROPERTY_PREFIXES = List.of(
+      "$.environment.", "$.environment[", "$.flags.", "$.flags[");
+
   private final FlagsmithLogger logger = new FlagsmithLogger();
   private FlagsmithSdk flagsmithSdk;
   private EvaluationContext evaluationContext;
+  @Getter(AccessLevel.NONE)
+  @Setter(AccessLevel.NONE)
+  @EqualsAndHashCode.Exclude
+  @ToString.Exclude
+  private EvaluationContext environmentEvaluationContext;
   private PollingManager pollingManager;
   @Getter(AccessLevel.PACKAGE)
   @Setter(AccessLevel.NONE)
@@ -58,6 +70,19 @@ public static FlagsmithClient.Builder newBuilder() {
     return new FlagsmithClient.Builder();
   }
 
+  /**
+   * Set the evaluation context, and derive the one environment flags evaluate against.
+   *
+   * @param evaluationContext the evaluation context
+   */
+  public void setEvaluationContext(EvaluationContext evaluationContext) {
+    this.environmentEvaluationContext = evaluationContext == null
+        ? null
+        : new EvaluationContext(evaluationContext)
+            .withSegments(getIdentityFreeSegments(evaluationContext.getSegments()));
+    this.evaluationContext = evaluationContext;
+  }
+
   /**
    * Load the environment flags in the environment variable from the API.
    */
@@ -68,7 +93,7 @@ public void updateEnvironment() {
       // if we didn't get an environment from the API,
       // then don't overwrite the copy we already have.
       if (updatedEvaluationContext != null) {
-        this.evaluationContext = updatedEvaluationContext;
+        setEvaluationContext(updatedEvaluationContext);
       } else {
         logger.error(getEnvironmentUpdateErrorMessage());
       }
@@ -411,24 +436,48 @@ private EventProcessor requireEventProcessor(String action) {
   }
 
   private Flags getEnvironmentFlagsFromEvaluationContext() throws FlagsmithClientError {
-    if (evaluationContext == null) {
+    final EvaluationContext context = environmentEvaluationContext;
+    if (context == null) {
       if (getConfig().getFlagsmithFlagDefaults() == null) {
         throw new FlagsmithClientError("Unable to get flags. No environment present.");
       }
       return getDefaultFlags();
     }
 
-    final EvaluationResult result = Engine.getEvaluationResult(
-      new EvaluationContext(evaluationContext)
-        .withSegments(null)
-    );
+    final EvaluationResult result = Engine.getEvaluationResult(context);
 
     return Flags.fromEvaluationResult(
         result,
         getConfig().getAnalyticsProcessor(),
         getConfig().getFlagsmithFlagDefaults());
   }
 
+  /*
+   * The segments that resolve without an identity, i.e. those whose every
+   * condition reads only the environment or other flags.
+   */
+  private static Segments getIdentityFreeSegments(Segments segments) {
+    if (segments == null) {
+      return null;
+    }
+    Segments identityFreeSegments = new Segments();
+    segments.getAdditionalProperties().forEach((segmentKey, segmentContext) -> {
+      if (isIdentityFree(segmentContext.getRules())) {
+        identityFreeSegments.setAdditionalProperty(segmentKey, segmentContext);
+      }
+    });
+    return identityFreeSegments;
+  }
+
+  private static boolean isIdentityFree(List<SegmentRule> rules) {
+    return rules == null || rules.stream().allMatch(rule ->
+        (rule.getConditions() == null || rule.getConditions().stream().allMatch(condition ->
+            condition.getProperty() != null
+                && IDENTITY_FREE_PROPERTY_PREFIXES.stream()
+                    .anyMatch(condition.getProperty()::startsWith)))
+            && isIdentityFree(rule.getRules()));
+  }
+
   private Flags getIdentityFlagsFromEvaluationContext(
       String identifier, Map<String, Object> traits)
       throws FlagsmithClientError {
@@ -748,8 +797,8 @@ public FlagsmithClient build() {
           throw new FlagsmithRuntimeError(
               "Cannot use both default flag handler and offline handler.");
         }
-        client.evaluationContext = EngineMappers.mapEnvironmentToContext(
-          configuration.getOfflineHandler().getEnvironment());
+        client.setEvaluationContext(EngineMappers.mapEnvironmentToContext(
+            configuration.getOfflineHandler().getEnvironment()));
       }
 
       EventProcessor processor = null;