Decouple App Hang backtrace generation from Crash Reporting

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 - [FEATURE] Add an experimental Core Animation recording pipeline for Session Replay, available through the `compositionTreeRecording` feature flag. See [#3127][]
 - [FEATURE] Add `disallowList` to `RUM.Configuration.URLSessionTracking` to exclude URLs from automatic RUM resource tracking, with `*` wildcard support. [#3097][]
+- [FEATURE] Add `CrashReporting.Configuration.appHangBacktraceEnabled` to opt out of stack trace collection in App Hang errors while keeping Crash Reporting enabled. See [#3136][]
 - [IMPROVEMENT] Forward `local_cache_hit` signal on RUM resources [#3074][]
 - [FIX] Fix `EXC_BREAKPOINT` crash when a log or RUM attribute's `encode(to:)` throws after partially encoding a value. [#3134][]
 
@@ -1227,6 +1228,7 @@ Release `2.0` introduces breaking changes. Follow the [Migration Guide](MIGRATIO
 [#3127]: https://github.com/DataDog/dd-sdk-ios/pull/3127
 [#3097]: https://github.com/DataDog/dd-sdk-ios/pull/3097
 [#3134]: https://github.com/DataDog/dd-sdk-ios/pull/3134
+[#3136]: https://github.com/DataDog/dd-sdk-ios/pull/3136
 
 [@00fa9a]: https://github.com/00FA9A
 [@britton-earnin]: https://github.com/Britton-Earnin

Datadog/Example/Base.lproj/Main iOS.storyboard

@@ -1369,6 +1369,65 @@
                                             <constraint firstAttribute="height" constant="20" id="WDI-xM-t2N"/>
                                         </constraints>
                                     </view>
+                                    <label opaque="NO" userInteractionEnabled="NO" contentMode="left" horizontalHuggingPriority="251" verticalHuggingPriority="251" text="App Hang" textAlignment="natural" lineBreakMode="tailTruncation" baselineAdjustment="alignBaselines" adjustsFontSizeToFit="NO" translatesAutoresizingMaskIntoConstraints="NO" id="Ah1-Ti-tLe">
+                                        <rect key="frame" x="0.0" y="392" width="384" height="20.5"/>
+                                        <fontDescription key="fontDescription" style="UICTFontTextStyleHeadline"/>
+                                        <nil key="textColor"/>
+                                        <nil key="highlightedColor"/>
+                                    </label>
+                                    <view contentMode="scaleToFill" translatesAutoresizingMaskIntoConstraints="NO" id="Ah2-Gp-g10" userLabel="Vertical gap 5">
+                                        <rect key="frame" x="0.0" y="412.5" width="384" height="5"/>
+                                        <color key="backgroundColor" systemColor="systemBackgroundColor"/>
+                                        <constraints>
+                                            <constraint firstAttribute="height" constant="5" id="Ah3-Cn-st5"/>
+                                        </constraints>
+                                    </view>
+                                    <label opaque="NO" userInteractionEnabled="NO" contentMode="left" horizontalHuggingPriority="251" verticalHuggingPriority="251" text="Backtraces: ON" textAlignment="natural" lineBreakMode="wordWrap" numberOfLines="0" baselineAdjustment="alignBaselines" adjustsFontSizeToFit="NO" translatesAutoresizingMaskIntoConstraints="NO" id="Ah4-St-lbl">
+                                        <rect key="frame" x="0.0" y="417.5" width="384" height="14.5"/>
+                                        <fontDescription key="fontDescription" style="UICTFontTextStyleCaption1"/>
+                                        <color key="textColor" systemColor="systemGrayColor"/>
+                                        <nil key="highlightedColor"/>
+                                    </label>
+                                    <view contentMode="scaleToFill" translatesAutoresizingMaskIntoConstraints="NO" id="Ah5-Gp-g10" userLabel="Vertical gap 10">
+                                        <rect key="frame" x="0.0" y="432" width="384" height="10"/>
+                                        <color key="backgroundColor" systemColor="systemBackgroundColor"/>
+                                        <constraints>
+                                            <constraint firstAttribute="height" constant="10" id="Ah6-Cn-st10"/>
+                                        </constraints>
+                                    </view>
+                                    <stackView opaque="NO" contentMode="scaleToFill" spacing="5" translatesAutoresizingMaskIntoConstraints="NO" id="Ah7-Sv-stk">
+                                        <rect key="frame" x="0.0" y="442" width="384" height="44"/>
+                                        <subviews>
+                                            <button opaque="NO" contentMode="scaleToFill" contentHorizontalAlignment="center" contentVerticalAlignment="center" lineBreakMode="middleTruncation" translatesAutoresizingMaskIntoConstraints="NO" id="Ah8-Bt-btn">
+                                                <rect key="frame" x="0.0" y="0.0" width="384" height="44"/>
+                                                <color key="backgroundColor" red="0.38823529410000002" green="0.17254901959999999" blue="0.65098039220000004" alpha="1" colorSpace="calibratedRGB"/>
+                                                <fontDescription key="fontDescription" style="UICTFontTextStyleBody"/>
+                                                <state key="normal" title="Hang main thread for 2s">
+                                                    <color key="titleColor" white="1" alpha="1" colorSpace="custom" customColorSpace="genericGamma22GrayColorSpace"/>
+                                                    <color key="titleShadowColor" white="0.0" alpha="0.0" colorSpace="custom" customColorSpace="genericGamma22GrayColorSpace"/>
+                                                </state>
+                                                <userDefinedRuntimeAttributes>
+                                                    <userDefinedRuntimeAttribute type="boolean" keyPath="layer.masksToBounds" value="YES"/>
+                                                    <userDefinedRuntimeAttribute type="number" keyPath="layer.cornerRadius">
+                                                        <integer key="value" value="7"/>
+                                                    </userDefinedRuntimeAttribute>
+                                                </userDefinedRuntimeAttributes>
+                                                <connections>
+                                                    <action selector="didTapHangMainThread:" destination="dzc-N5-XBR" eventType="touchUpInside" id="Ah9-Ac-act"/>
+                                                </connections>
+                                            </button>
+                                        </subviews>
+                                        <constraints>
+                                            <constraint firstAttribute="height" constant="44" id="AhA-Cn-h44"/>
+                                        </constraints>
+                                    </stackView>
+                                    <view contentMode="scaleToFill" translatesAutoresizingMaskIntoConstraints="NO" id="AhB-Gp-g20" userLabel="Vertical gap 20">
+                                        <rect key="frame" x="0.0" y="486" width="384" height="20"/>
+                                        <color key="backgroundColor" systemColor="systemBackgroundColor"/>
+                                        <constraints>
+                                            <constraint firstAttribute="height" constant="20" id="AhC-Cn-h20"/>
+                                        </constraints>
+                                    </view>
                                 </subviews>
                             </stackView>
                         </subviews>
@@ -1382,6 +1441,7 @@
                     </view>
                     <navigationItem key="navigationItem" id="UG5-SU-NkM"/>
                     <connections>
+                        <outlet property="appHangBacktraceStatusLabel" destination="Ah4-St-lbl" id="AhD-Ou-out"/>
                         <outlet property="rumServiceNameTextField" destination="Bco-7y-w7S" id="cBg-pr-cZ4"/>
                         <outlet property="viewNameTextField" destination="bXI-gy-gbl" id="ZaZ-Sh-Nrd"/>
                     </connections>

Datadog/Example/Debugging/DebugCrashReportingWithRUMViewController.swift

@@ -14,6 +14,9 @@ class DebugCrashReportingWithRUMViewController: UIViewController {
         super.viewDidLoad()
         rumServiceNameTextField.text = serviceName
         viewNameTextField.placeholder = viewName
+        appHangBacktraceStatusLabel.text = Environment.isAppHangBacktraceEnabled()
+            ? "Backtraces: ON — launch with `DD_DISABLE_APP_HANG_BACKTRACES` to turn them off"
+            : "Backtraces: OFF — `appHangBacktraceEnabled: false`"
     }
 
     private func crash() {
@@ -48,6 +51,22 @@ class DebugCrashReportingWithRUMViewController: UIViewController {
         }
     }
 
+    // MARK: - App Hang
+
+    @IBOutlet weak var appHangBacktraceStatusLabel: UILabel!
+
+    /// Blocks the main thread for longer than the `appHangThreshold` configured in `ExampleAppDelegate`,
+    /// so RUM reports an App Hang error. Whether that error carries a stack trace depends on
+    /// `CrashReporting.Configuration.appHangBacktraceEnabled`.
+    @IBAction func didTapHangMainThread(_ sender: Any) {
+        (sender as? UIButton)?.disableFor(seconds: 0.5)
+
+        rumMonitor.startView(key: viewName, name: viewName, attributes: [:])
+        DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
+            Thread.sleep(forTimeInterval: 2)
+        }
+    }
+
     // MARK: - OOM Crash
 
     @IBAction func didTapOOMCrash(_ sender: UIButton) {

Datadog/Example/Environment.swift

@@ -11,6 +11,8 @@ internal struct Environment {
     struct Argument {
         static let isRunningUnitTests       = "IS_RUNNING_UNIT_TESTS"
         static let isRunningUITests         = "IS_RUNNING_UI_TESTS"
+        /// Launches the app with `CrashReporting.Configuration.appHangBacktraceEnabled` set to `false`.
+        static let disableAppHangBacktraces = "DD_DISABLE_APP_HANG_BACKTRACES"
     }
 
     struct InfoPlistKey {
@@ -37,6 +39,13 @@ internal struct Environment {
         return !isRunningUITests() && !isRunningUnitTests()
     }
 
+    /// Whether App Hangs detected by RUM should carry a stack trace.
+    ///
+    /// Add `DD_DISABLE_APP_HANG_BACKTRACES` to the scheme's launch arguments to exercise the opt-out.
+    static func isAppHangBacktraceEnabled() -> Bool {
+        return !ProcessInfo.processInfo.arguments.contains(Argument.disableAppHangBacktraces)
+    }
+
     // MARK: - Info.plist
 
     static func readClientToken() -> String {

Datadog/Example/ExampleAppDelegate.swift

@@ -61,7 +61,11 @@ class ExampleAppDelegate: UIResponder, UIApplicationDelegate {
         )
 
         // Enable Crash Reporting
-        CrashReporting.enable()
+        CrashReporting.enable(
+            with: CrashReporting.Configuration(
+                appHangBacktraceEnabled: Environment.isAppHangBacktraceEnabled()
+            )
+        )
 
         // Set highest verbosity level to see debugging logs from the SDK
         Datadog.verbosityLevel = .debug
@@ -87,6 +91,7 @@ class ExampleAppDelegate: UIResponder, UIApplicationDelegate {
                     }
                 ),
                 trackBackgroundEvents: true,
+                appHangThreshold: 0.5,
                 trackWatchdogTerminations: true,
                 customEndpoint: Environment.readCustomRUMURL(),
                 telemetrySampleRate: 100

Datadog/IntegrationUnitTests/CrashReporting/GeneratingBacktraceTests.swift

@@ -59,6 +59,29 @@ class GeneratingBacktraceTests: XCTestCase {
         )
     }
 
+    func testGivenAppHangBacktracesDisabled_whenGeneratingBacktrace_itStillGeneratesIt() throws {
+        #if os(watchOS)
+        throw XCTSkip("Backtrace generation is not supported on watchOS")
+        #endif
+        // Given
+        CrashReporting.enable(with: .init(appHangBacktraceEnabled: false), in: core)
+
+        // Then
+        XCTAssertNotNil(core.get(feature: BacktraceReportingFeature.self), "`BacktraceReportingFeature` must still be registered")
+        XCTAssertFalse(core.isAppHangBacktraceEnabled)
+
+        // Only the App Hangs consumer is gated - other consumers must keep working:
+        let backtrace = try XCTUnwrap(core.backtraceReporter.generateBacktrace())
+        XCTAssertGreaterThan(backtrace.threads.count, 0, "Some thread(s) should be recorded")
+        XCTAssertGreaterThan(backtrace.binaryImages.count, 0, "Some binary image(s) should be recorded")
+    }
+
+    func testGivenCrashReportingNotEnabled_thenAppHangBacktracesAreNotDisabled() {
+        // Then (backtrace generation is *unavailable*, not *disabled*)
+        XCTAssertNil(core.get(feature: BacktraceReportingFeature.self))
+        XCTAssertTrue(core.isAppHangBacktraceEnabled)
+    }
+
     func testGeneratingBacktraceOfTheMainThread() throws {
         #if os(watchOS)
         throw XCTSkip("Backtrace generation is not supported on watchOS")

Datadog/IntegrationUnitTests/RUM/AppHangsMonitoringTests.swift

@@ -116,6 +116,48 @@ class AppHangsMonitoringTests: XCTestCase {
         #endif
     }
 
+    func testGivenAppHangBacktracesDisabledInCrashReporting_whenRUMIsEnabledFirst_itTracksAppHangWithNoStackTrace() throws {
+        try assertAppHangIsTrackedWithNoStackTrace { crashReportingConfig in
+            RUM.enable(with: self.rumConfig, in: self.core)
+            CrashReporting.enable(with: crashReportingConfig, in: self.core)
+        }
+    }
+
+    func testGivenAppHangBacktracesDisabledInCrashReporting_whenCrashReportingIsEnabledFirst_itTracksAppHangWithNoStackTrace() throws {
+        try assertAppHangIsTrackedWithNoStackTrace { crashReportingConfig in
+            CrashReporting.enable(with: crashReportingConfig, in: self.core)
+            RUM.enable(with: self.rumConfig, in: self.core)
+        }
+    }
+
+    /// Asserts that a hang is tracked with no stack trace, with the SDK enabled by `enableSDK`.
+    ///
+    /// Both enablement orders get their own test rather than being picked at random: only the RUM-first order
+    /// proves that the opt-out is read per hang instead of being captured when RUM is enabled, so randomizing
+    /// would let that regression pass half of the runs.
+    private func assertAppHangIsTrackedWithNoStackTrace(enableSDK: (CrashReporting.Configuration) -> Void) throws {
+        // Given (initialize SDK on the main thread)
+        enableSDK(CrashReporting.Configuration(appHangBacktraceEnabled: false))
+
+        // When
+        mainQueue.sync {
+            Thread.sleep(forTimeInterval: hangDuration)
+        }
+
+        // Then
+        try flushHangsMonitoring()
+        let errors = core.waitAndReturnEvents(ofFeature: RUMFeature.name, ofType: RUMErrorEvent.self)
+        let appHangError = try XCTUnwrap(errors.first)
+
+        XCTAssertEqual(appHangError.error.message, AppHangsMonitor.Constants.appHangErrorMessage)
+        XCTAssertEqual(appHangError.error.type, AppHangsMonitor.Constants.appHangErrorType)
+        XCTAssertEqual(appHangError.error.stack, AppHangsMonitor.Constants.appHangStackDisabledErrorMessage)
+        XCTAssertEqual(appHangError.error.source, .source)
+        XCTAssertNil(appHangError.error.threads, "Threads should be unavailable as App Hang backtraces were disabled")
+        XCTAssertNil(appHangError.error.binaryImages, "Binary Images should be unavailable as App Hang backtraces were disabled")
+        XCTAssertNil(appHangError.error.wasTruncated, "Truncation flag should be unavailable as App Hang backtraces were disabled")
+    }
+
     func testGivenOnlyRUMEnabled_whenMainThreadHangs_itTracksAppHangWithNoStackTrace() throws {
         // Given
         mainQueue.sync {

DatadogCore/Tests/Objc/ObjcAPITests/DDConfiguration+apiTests.m

@@ -73,6 +73,13 @@ - (void)testDDConfigurationBuilderAPI {
 
 - (void)testDatadogCrashReporterAPI {
     [DDCrashReporter enable];
+
+    DDCrashReporterConfiguration *configuration = [DDCrashReporterConfiguration new];
+    XCTAssertTrue(configuration.appHangBacktraceEnabled, @"App Hang backtraces are enabled by default");
+    configuration.appHangBacktraceEnabled = NO;
+    XCTAssertFalse(configuration.appHangBacktraceEnabled, @"The setter must write through to the wrapped configuration");
+
+    [DDCrashReporter enableWith:configuration];
 }
 
 #pragma clang diagnostic pop