Add metadata field to FlagDetails and populate allocationKey

DatadogFlags/Sources/Client/FlagsClient.swift

@@ -248,11 +248,19 @@ extension FlagsClient: FlagsClientProtocol {
             return FlagDetails(key: key, value: defaultValue, error: .typeMismatch)
         }
 
+        var metadata: [String: AnyValue] = [:]
+        for (logKey, value) in flagAssignment.extraLogging {
+            metadata[logKey] = value
+        }
+        // Written last so it always wins over any extraLogging value with the same key.
+        metadata["allocationKey"] = .string(flagAssignment.allocationKey)
+
         let details = FlagDetails(
             key: key,
             value: value,
             variant: flagAssignment.variationKey,
-            reason: flagAssignment.reason
+            reason: flagAssignment.reason,
+            metadata: metadata
         )
 
         trackEvaluation(key: key, assignment: flagAssignment, context: context)

DatadogFlags/Sources/Models/FlagAssignment.swift

@@ -21,6 +21,7 @@ public struct FlagAssignment: Equatable {
     public var variation: Variation
     public var reason: String
     public var doLog: Bool
+    public var extraLogging: [String: AnyValue]
 
     func variation<T: FlagValue>(as type: T.Type) -> T? {
         switch self.variation {
@@ -39,12 +40,20 @@ public struct FlagAssignment: Equatable {
         }
     }
 
-    public init(allocationKey: String, variationKey: String, variation: Variation, reason: String, doLog: Bool) {
+    public init(
+        allocationKey: String,
+        variationKey: String,
+        variation: Variation,
+        reason: String,
+        doLog: Bool,
+        extraLogging: [String: AnyValue] = [:]
+    ) {
         self.allocationKey = allocationKey
         self.variationKey = variationKey
         self.variation = variation
         self.reason = reason
         self.doLog = doLog
+        self.extraLogging = extraLogging
     }
 }
 
@@ -56,6 +65,7 @@ extension FlagAssignment: Codable {
         case variationValue
         case reason
         case doLog
+        case extraLogging
     }
 
     public init(from decoder: any Decoder) throws {
@@ -65,6 +75,7 @@ extension FlagAssignment: Codable {
         self.variationKey = try container.decode(String.self, forKey: .variationKey)
         self.reason = try container.decode(String.self, forKey: .reason)
         self.doLog = try container.decode(Bool.self, forKey: .doLog)
+        self.extraLogging = try container.decodeIfPresent([String: AnyValue].self, forKey: .extraLogging) ?? [:]
 
         let variationType = try container.decode(String.self, forKey: .variationType)
 
@@ -99,6 +110,9 @@ extension FlagAssignment: Codable {
         try container.encode(variationKey, forKey: .variationKey)
         try container.encode(reason, forKey: .reason)
         try container.encode(doLog, forKey: .doLog)
+        if !extraLogging.isEmpty {
+            try container.encode(extraLogging, forKey: .extraLogging)
+        }
 
         switch variation {
         case .boolean(let value):

DatadogFlags/Sources/Models/FlagDetails.swift

@@ -4,8 +4,6 @@
  * Copyright 2019-Present Datadog, Inc.
  */
 
-import Foundation
-
 /// An error tha occurs during feature flag evaluation.
 ///
 /// Indicates why a flag evaluation may have failed or returned a default value.
@@ -71,6 +69,11 @@ public struct FlagDetails<T>: Equatable where T: Equatable {
     /// value is from a successful evaluation or a fallback to the default value.
     public var error: FlagEvaluationError?
 
+    /// Additional metadata about the flag evaluation.
+    ///
+    /// Contains fields from the flag assignment such as `allocationKey` and `extraLogging` values.
+    public var metadata: [String: AnyValue]
+
     /// Creates detailed flag evaluation information.
     ///
     /// - Parameters:
@@ -79,17 +82,20 @@ public struct FlagDetails<T>: Equatable where T: Equatable {
     ///   - variant: The variant key served, if any.
     ///   - reason: The evaluation reason, if available.
     ///   - error: Any error that occurred during evaluation.
+    ///   - metadata: Additional metadata about the evaluation, such as `allocationKey`.
     public init(
         key: String,
         value: T,
         variant: String? = nil,
         reason: String? = nil,
-        error: FlagEvaluationError? = nil
+        error: FlagEvaluationError? = nil,
+        metadata: [String: AnyValue] = [:]
     ) {
         self.key = key
         self.value = value
         self.variant = variant
         self.reason = reason
         self.error = error
+        self.metadata = metadata
     }
 }

DatadogFlags/Tests/Client/FlagsClientTests.swift

@@ -232,7 +232,8 @@ final class FlagsClientTests: XCTestCase {
                 key: "boolean-flag",
                 value: true,
                 variant: "variation-124",
-                reason: "TARGETING_MATCH"
+                reason: "TARGETING_MATCH",
+                metadata: ["allocationKey": .string("allocation-124")]
             )
         )
         XCTAssertEqual(
@@ -479,6 +480,130 @@ final class FlagsClientTests: XCTestCase {
         XCTAssertNil(flagAssignments["missing-flag"])
     }
 
+    func testGetDetails_includesAllocationKeyInMetadata() {
+        // Given
+        let repository = FlagsRepositoryMock(
+            flagsData: .init(
+                flags: [
+                    "feature-flag": .init(
+                        allocationKey: "alloc-abc",
+                        variationKey: "variation-1",
+                        variation: .boolean(true),
+                        reason: "TARGETING_MATCH",
+                        doLog: false,
+                        extraLogging: [
+                            "experimentName": .string("exp-1"),
+                            "sampleRate": .double(0.5),
+                            "bucketIndex": .int(7),
+                            "isControl": .bool(false),
+                        ]
+                    )
+                ],
+                context: .mockAny(),
+                date: .mockAny()
+            )
+        )
+        let client = FlagsClient(
+            repository: repository,
+            exposureLogger: ExposureLoggerMock(),
+            evaluationLogger: EvaluationLoggerMock(),
+            rumFlagEvaluationReporter: RUMFlagEvaluationReporterMock()
+        )
+
+        // When
+        let details = client.getDetails(key: "feature-flag", defaultValue: false)
+
+        // Then — typed allocationKey field always present
+        XCTAssertEqual(details.metadata["allocationKey"], .string("alloc-abc"))
+        // Then — extraLogging values are merged into metadata
+        XCTAssertEqual(details.metadata["experimentName"], .string("exp-1"))
+        XCTAssertEqual(details.metadata["sampleRate"], .double(0.5))
+        XCTAssertEqual(details.metadata["bucketIndex"], .int(7))
+        XCTAssertEqual(details.metadata["isControl"], .bool(false))
+    }
+
+    func testGetDetails_errorPathsHaveEmptyMetadata() {
+        // Given — a client with no context (providerNotReady) and one string flag (for typeMismatch)
+        let providerNotReadyClient = FlagsClient(
+            repository: FlagsRepositoryMock(),
+            exposureLogger: ExposureLoggerMock(),
+            evaluationLogger: EvaluationLoggerMock(),
+            rumFlagEvaluationReporter: RUMFlagEvaluationReporterMock()
+        )
+
+        let clientWithFlags = FlagsClient(
+            repository: FlagsRepositoryMock(
+                flagsData: .init(
+                    flags: [
+                        "string-flag": .init(
+                            allocationKey: "allocation-123",
+                            variationKey: "variation-123",
+                            variation: .string("red"),
+                            reason: "TARGETING_MATCH",
+                            doLog: false
+                        )
+                    ],
+                    context: .mockAny(),
+                    date: .mockAny()
+                )
+            ),
+            exposureLogger: ExposureLoggerMock(),
+            evaluationLogger: EvaluationLoggerMock(),
+            rumFlagEvaluationReporter: RUMFlagEvaluationReporterMock()
+        )
+
+        // When
+        let providerNotReadyDetails = providerNotReadyClient.getDetails(key: "any-flag", defaultValue: false)
+        let flagNotFoundDetails = clientWithFlags.getDetails(key: "missing-flag", defaultValue: false)
+        let typeMismatchDetails = clientWithFlags.getDetails(key: "string-flag", defaultValue: false)
+
+        // Then — all error paths return empty metadata
+        XCTAssertEqual(providerNotReadyDetails.error, .providerNotReady)
+        XCTAssertTrue(providerNotReadyDetails.metadata.isEmpty)
+
+        XCTAssertEqual(flagNotFoundDetails.error, .flagNotFound)
+        XCTAssertTrue(flagNotFoundDetails.metadata.isEmpty)
+
+        XCTAssertEqual(typeMismatchDetails.error, .typeMismatch)
+        XCTAssertTrue(typeMismatchDetails.metadata.isEmpty)
+    }
+
+    func testGetDetails_extraLoggingAllocationKeyDoesNotOverrideTypedAllocationKey() {
+        // Given — extraLogging contains an "allocationKey" key that will be overwritten by the typed field
+        let repository = FlagsRepositoryMock(
+            flagsData: .init(
+                flags: [
+                    "feature-flag": .init(
+                        allocationKey: "real-alloc-key",
+                        variationKey: "variation-1",
+                        variation: .boolean(true),
+                        reason: "TARGETING_MATCH",
+                        doLog: false,
+                        extraLogging: [
+                            "allocationKey": .string("fake-alloc-key"),
+                            "other": .string("value"),
+                        ]
+                    )
+                ],
+                context: .mockAny(),
+                date: .mockAny()
+            )
+        )
+        let client = FlagsClient(
+            repository: repository,
+            exposureLogger: ExposureLoggerMock(),
+            evaluationLogger: EvaluationLoggerMock(),
+            rumFlagEvaluationReporter: RUMFlagEvaluationReporterMock()
+        )
+
+        // When
+        let details = client.getDetails(key: "feature-flag", defaultValue: false)
+
+        // Then — typed field wins; allocationKey is written last so it overwrites any extraLogging value
+        XCTAssertEqual(details.metadata["allocationKey"], .string("real-alloc-key"))
+        XCTAssertEqual(details.metadata["other"], .string("value"))
+    }
+
     func testSendFlagEvaluation() {
         // Given
         let exposureLogger = ExposureLoggerMock()

DatadogFlags/Tests/Models/FlagAssignmentsResponseTests.swift

@@ -110,35 +110,40 @@ final class FlagAssignmentsResponseTests: XCTestCase {
                         variationKey: "variation-123",
                         variation: .string("red"),
                         reason: "TARGETING_MATCH",
-                        doLog: true
+                        doLog: true,
+                        extraLogging: ["experiment": .bool(true)]
                     ),
                     "boolean-flag": .init(
                         allocationKey: "allocation-124",
                         variationKey: "variation-124",
                         variation: .boolean(true),
                         reason: "TARGETING_MATCH",
-                        doLog: true
+                        doLog: true,
+                        extraLogging: ["experiment": .bool(true)]
                     ),
                     "integer-flag": .init(
                         allocationKey: "allocation-125",
                         variationKey: "variation-125",
                         variation: .integer(42),
                         reason: "TARGETING_MATCH",
-                        doLog: true
+                        doLog: true,
+                        extraLogging: ["experiment": .bool(true)]
                     ),
                     "numeric-flag": .init(
                         allocationKey: "allocation-126",
                         variationKey: "variation-126",
                         variation: .double(3.14),
                         reason: "TARGETING_MATCH",
-                        doLog: true
+                        doLog: true,
+                        extraLogging: ["experiment": .bool(true)]
                     ),
                     "legacy-number-flag": .init(
                         allocationKey: "allocation-128",
                         variationKey: "variation-128",
                         variation: .integer(99),
                         reason: "TARGETING_MATCH",
-                        doLog: true
+                        doLog: true,
+                        extraLogging: ["experiment": .bool(true)]
                     ),
                     "json-flag": .init(
                         allocationKey: "allocation-127",
@@ -148,13 +153,65 @@ final class FlagAssignmentsResponseTests: XCTestCase {
                             "prop": .int(123),
                         ])),
                         reason: "TARGETING_MATCH",
-                        doLog: true
+                        doLog: true,
+                        extraLogging: ["experiment": .bool(true)]
                     ),
                 ]
             )
         )
     }
 
+    func testDecodingFlagAssignmentWithExtraLogging() throws {
+        // Given
+        let json = """
+        {
+          "allocationKey": "allocation-abc",
+          "variationKey": "variation-abc",
+          "variationType": "string",
+          "variationValue": "blue",
+          "doLog": true,
+          "reason": "TARGETING_MATCH",
+          "extraLogging": {
+            "experimentName": "exp-42",
+            "sampleRate": 0.25,
+            "bucketIndex": 3,
+            "isControl": false
+          }
+        }
+        """.data(using: .utf8)!
+
+        // When
+        let assignment = try JSONDecoder().decode(FlagAssignment.self, from: json)
+
+        // Then
+        XCTAssertEqual(assignment.allocationKey, "allocation-abc")
+        XCTAssertEqual(assignment.variationKey, "variation-abc")
+        XCTAssertEqual(assignment.extraLogging["experimentName"], .string("exp-42"))
+        XCTAssertEqual(assignment.extraLogging["sampleRate"], .double(0.25))
+        XCTAssertEqual(assignment.extraLogging["bucketIndex"], .int(3))
+        XCTAssertEqual(assignment.extraLogging["isControl"], .bool(false))
+    }
+
+    func testDecodingFlagAssignmentWithoutExtraLogging() throws {
+        // Given — response from an older API that does not include extraLogging
+        let json = """
+        {
+          "allocationKey": "allocation-xyz",
+          "variationKey": "variation-xyz",
+          "variationType": "boolean",
+          "variationValue": true,
+          "doLog": false,
+          "reason": "DEFAULT"
+        }
+        """.data(using: .utf8)!
+
+        // When
+        let assignment = try JSONDecoder().decode(FlagAssignment.self, from: json)
+
+        // Then — extraLogging defaults to empty dict, no error
+        XCTAssertEqual(assignment.extraLogging, [:])
+    }
+
     func testDecodingFlagAssignmentsResponseWithUnknownVariationTypes() throws {
         // Given
         let json = """

api-surface-swift

@@ -1530,7 +1530,8 @@ public struct FlagAssignment: Equatable
     public var variation: Variation
     public var reason: String
     public var doLog: Bool
-    public init(allocationKey: String, variationKey: String, variation: Variation, reason: String, doLog: Bool)
+    public var extraLogging: [String: AnyValue]
+    public init(allocationKey: String,variationKey: String,variation: Variation,reason: String,doLog: Bool,extraLogging: [String: AnyValue] = [:])
     public init(from decoder: any Decoder) throws
     public func encode(to encoder: any Encoder) throws
 public enum FlagEvaluationError: Error
@@ -1543,7 +1544,8 @@ public struct FlagDetails<T>: Equatable where T: Equatable
     public var variant: String?
     public var reason: String?
     public var error: FlagEvaluationError?
-    public init(key: String,value: T,variant: String? = nil,reason: String? = nil,error: FlagEvaluationError? = nil)
+    public var metadata: [String: AnyValue]
+    public init(key: String,value: T,variant: String? = nil,reason: String? = nil,error: FlagEvaluationError? = nil,metadata: [String: AnyValue] = [:])
 public protocol FlagValue: Encodable
 public enum FlagsError: Error
     case networkError(Error)