[FirebaseMessaging] Fix crash on Xcode 26 + iOS 18 (#15164)

Author: subdiox

FirebaseInAppMessaging/Sources/Runtime/FIRIAMActionURLFollower.m

@@ -175,8 +175,10 @@ - (BOOL)followURLWithContinueUserActivity:(NSURL *)url {
     FIRLogDebug(kFIRLoggerInAppMessaging, @"I-IAM240004",
                 @"App delegate responds to application:continueUserActivity:restorationHandler:."
                  "Simulating action url opening from a web browser.");
+    // Use string literal to ensure compatibility with Xcode 26 and iOS 18
+    NSString *browsingWebType = @"NSUserActivityTypeBrowsingWeb";
     NSUserActivity *userActivity =
-        [[NSUserActivity alloc] initWithActivityType:NSUserActivityTypeBrowsingWeb];
+        [[NSUserActivity alloc] initWithActivityType:browsingWebType];
     userActivity.webpageURL = url;
     BOOL handled = [self.appDelegate application:self.mainApplication
                             continueUserActivity:userActivity

FirebaseInAppMessaging/Tests/Unit/FIRIAMActionUrlFollowerTests.m

@@ -84,8 +84,10 @@ - (void)testUniversalLinkHandlingReturnYES {
                          continueUserActivity:[OCMArg checkWithBlock:^BOOL(id userActivity) {
                            // verifying the type and url field for the userActivity object
                            NSUserActivity *activity = (NSUserActivity *)userActivity;
+                           // Use string literal to ensure compatibility with Xcode 26 and iOS 18
+                           NSString *browsingWebType = @"NSUserActivityTypeBrowsingWeb";
                            return [activity.activityType
-                                      isEqualToString:NSUserActivityTypeBrowsingWeb] &&
+                                      isEqualToString:browsingWebType] &&
                                   [activity.webpageURL isEqual:url];
                          }]
                            restorationHandler:[OCMArg any]])

FirebaseMessaging/Sources/FIRMessaging.m

@@ -400,8 +400,10 @@ - (void)handleIncomingLinkIfNeededFromMessage:(NSDictionary *)message {
   // if they haven't implemented it.
   if ([NSUserActivity class] != nil &&
       [appDelegate respondsToSelector:continueUserActivitySelector]) {
+    // Use string literal to ensure compatibility with Xcode 26 and iOS 18
+    NSString *browsingWebType = @"NSUserActivityTypeBrowsingWeb";
     NSUserActivity *userActivity =
-        [[NSUserActivity alloc] initWithActivityType:NSUserActivityTypeBrowsingWeb];
+        [[NSUserActivity alloc] initWithActivityType:browsingWebType];
     userActivity.webpageURL = url;
     [appDelegate application:application
         continueUserActivity:userActivity