fix(ttd): Gracefully handle missing parentSpanId when measuring TTID/TTFD on iOS (#4881)

Author: krystofwoldrich

CHANGELOG.md

@@ -43,6 +43,7 @@
 - crashedLastRun now returns the correct value ([#4829](https://github.com/getsentry/sentry-react-native/pull/4829))
 - Use engine-specific promise rejection tracking ([#4826](https://github.com/getsentry/sentry-react-native/pull/4826))
 - Fixes Feedback Widget accessibility issue on iOS ([#4739](https://github.com/getsentry/sentry-react-native/pull/4739))
+- Measuring TTID or TTFD could cause a crash when `parentSpanId` was removed ([#4881](https://github.com/getsentry/sentry-react-native/pull/4881))
 
 ### Dependencies
 

packages/core/RNSentryCocoaTester/RNSentryCocoaTesterTests/RNSentryOnDrawReporterTests.swift

@@ -119,4 +119,30 @@ final class RNSentryOnDrawReporterTests: XCTestCase {
 
         XCTAssertNil(RNSentryTimeToDisplay.pop(for: ttidPrefix + spanId))
     }
+
+    func testFullDisplayEmitNewFrameCallbackHandlesMissingParentSpanId() {
+        let reporter = RNSentryOnDrawReporterView.createWithMockedListener()
+
+        // We call the callback manually in this test to simulate a change between
+        // start of listening for next frame and the next frame render
+        let emitNewFrameCallback = reporter!.createEmitNewFrameEvent()
+
+        reporter!.fullDisplay = true
+        reporter!.parentSpanId = nil
+
+        emitNewFrameCallback!(1)
+    }
+
+    func testInitialDisplayEmitNewFrameCallbackHandlesMissingParentSpanId() {
+        let reporter = RNSentryOnDrawReporterView.createWithMockedListener()
+
+        // We call the callback manually in this test to simulate a change between
+        // start of listening for next frame and the next frame render
+        let emitNewFrameCallback = reporter!.createEmitNewFrameEvent()
+
+        reporter!.initialDisplay = true
+        reporter!.parentSpanId = nil
+
+        emitNewFrameCallback!(1)
+    }
 }

packages/core/ios/RNSentryOnDrawReporter.m

@@ -42,6 +42,10 @@ - (RNSentryEmitNewFrameEvent)createEmitNewFrameEvent
     return ^(NSNumber *newFrameTimestampInSeconds) {
         self->isListening = NO;
 
+        if (![_parentSpanId isKindOfClass:[NSString class]]) {
+            return;
+        }
+
         if (self->_fullDisplay) {
             [RNSentryTimeToDisplay
                 putTimeToDisplayFor:[@"ttfd-" stringByAppendingString:self->_parentSpanId]