fix(crashlytics, ios): warn if debugger will break crashlytics

debuggers intercept crashes in iOS, leading to developer confusion.

packages/crashlytics/ios/RNFBCrashlytics/RNFBCrashlyticsModule.m

@@ -15,7 +15,11 @@
  *
  */
 
+#include <Foundation/Foundation.h>
+#include <sys/sysctl.h>
+
 #import <React/RCTUtils.h>
+#import <React/RCTLog.h>
 
 #import "RNFBCrashlyticsModule.h"
 #import "RNFBCrashlyticsInitProvider.h"
@@ -33,6 +37,9 @@ - (NSDictionary *)constantsToExport {
   NSMutableDictionary *constants = [NSMutableDictionary new];
   constants[@"isCrashlyticsCollectionEnabled"] = @([RCTConvert BOOL:@([RNFBCrashlyticsInitProvider isCrashlyticsCollectionEnabled])]);
   constants[@"isErrorGenerationOnJSCrashEnabled"] = @([RCTConvert BOOL:@([RNFBCrashlyticsInitProvider isErrorGenerationOnJSCrashEnabled])]);
+  if ([self isDebuggerAttached]) {
+    RCTLog(@"@react-native-firebase/crashlytics - WARNING: Debugger detected. Crashlytics will not receive crash reports.");
+  }
   return constants;
 }
 
@@ -54,6 +61,10 @@ + (BOOL)requiresMainQueueSetup {
 
 RCT_EXPORT_METHOD(crash) {
   if ([RNFBCrashlyticsInitProvider isCrashlyticsCollectionEnabled]) {
+    if ([self isDebuggerAttached]) {
+      RCTLog(@"@react-native-firebase/crashlytics - WARNING: Debugger detected. Crashlytics will not receive crash reports.");
+    }
+
     // https://firebase.google.com/docs/crashlytics/test-implementation?platform=ios recommends using "@[][1]" to crash,
     // but that gets caught by react-native and shown as a red box for debug builds. Raise SIGSEGV here to generate a hard crash.
     int *p = 0;
@@ -185,5 +196,37 @@ - (void)recordJavaScriptError:(NSDictionary *)jsErrorDict {
   [[FIRCrashlytics crashlytics] recordExceptionModel:exceptionModel];
 }
 
+/**
+ * Check if the debugger is attached
+ *
+ * Taken from https://github.com/plausiblelabs/plcrashreporter/blob/2dd862ce049e6f43feb355308dfc710f3af54c4d/Source/Crash%20Demo/main.m#L96
+ *
+ * @return `YES` if the debugger is attached to the current process, `NO` otherwise
+ */
+- (BOOL)isDebuggerAttached {
+  static BOOL debuggerIsAttached = NO;
+
+  static dispatch_once_t debuggerPredicate;
+  dispatch_once(&debuggerPredicate, ^{
+    struct kinfo_proc info;
+    size_t info_size = sizeof(info);
+    int name[4];
+
+    name[0] = CTL_KERN;
+    name[1] = KERN_PROC;
+    name[2] = KERN_PROC_PID;
+    name[3] = getpid(); // from unistd.h, included by Foundation
+
+    if (sysctl(name, 4, &info, &info_size, NULL, 0) == -1) {
+      RCTLog(@"@react-native-firebase/crashlytics ERROR: Checking for a running debugger via sysctl() failed: %s", strerror(errno));
+      debuggerIsAttached = false;
+    }
+
+    if (!debuggerIsAttached && (info.kp_proc.p_flag & P_TRACED) != 0)
+      debuggerIsAttached = true;
+  });
+
+  return debuggerIsAttached;
+}
 
 @end