From ba5015104dac25c4af56d661fcb6d54e4f30915f Mon Sep 17 00:00:00 2001
From: Zack Sheppard <zack.sheppard@candidco.com>
Date: Thu, 6 Dec 2018 20:19:06 -0800
Subject: [PATCH] Extend reason message for `RCTFatalException` (#22532)

Summary:
Fixes #22530

As described in the issue, the previous behavior for the `RCTFatal` macro was to truncate the `reason` on the resulting `NSException` to 75 characters. This would ensure the reason would fit on a single line, but resulted in issues debugging errors that occurred in the wild, as many crash logging tools (like Sentry) discard the `name` value of the exception and use the `reason` as their primary identifier. At 75 characters, useful information like the location of the error would usually be truncated.

- [x] This extends the truncation threshold to 175 characters, which should be short enough to prevent full-screen-takeover length errors, but long enough to provide useful context to the error.
- [x] This adds a `userInfo` value to the resulting `NSException`. It copies over the `userInfo` from the `NSError` passed to the macro, and adds an "untruncated message" value that contains the untruncated version of the `NSException`'s reason.

[iOS] [Changed] - RCTFatalExceptions now include more information in their reason and a userInfo.

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Pull Request resolved: https://github.com/facebook/react-native/pull/22532

Differential Revision: D13373469

Pulled By: cpojer

fbshipit-source-id: ac140d14ce76e1664869437c2c178bdd65ab6e0e
---
 React/Base/RCTAssert.m | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/React/Base/RCTAssert.m b/React/Base/RCTAssert.m
index 61cefe2ad5fca2..13db0a598fd871 100644
--- a/React/Base/RCTAssert.m
+++ b/React/Base/RCTAssert.m
@@ -12,6 +12,7 @@
 NSString *const RCTJSStackTraceKey = @"RCTJSStackTraceKey";
 NSString *const RCTJSRawStackTraceKey = @"RCTJSRawStackTraceKey";
 NSString *const RCTFatalExceptionName = @"RCTFatalException";
+NSString *const RCTUntruncatedMessageKey = @"RCTUntruncatedMessageKey";
 
 static NSString *const RCTAssertFunctionStack = @"RCTAssertFunctionStack";
 
@@ -128,8 +129,20 @@ void RCTFatal(NSError *error)
     @try {
 #endif
       NSString *name = [NSString stringWithFormat:@"%@: %@", RCTFatalExceptionName, error.localizedDescription];
-      NSString *message = RCTFormatError(error.localizedDescription, error.userInfo[RCTJSStackTraceKey], 75);
-      @throw [[NSException alloc]  initWithName:name reason:message userInfo:nil];
+
+      // Truncate the localized description to 175 characters to avoid wild screen overflows
+      NSString *message = RCTFormatError(error.localizedDescription, error.userInfo[RCTJSStackTraceKey], 175);
+
+      // Attach an untruncated copy of the description to the userInfo, in case it is needed
+      NSMutableDictionary *userInfo = [error.userInfo mutableCopy];
+      [userInfo setObject:RCTFormatError(error.localizedDescription, error.userInfo[RCTJSStackTraceKey], -1)
+                   forKey:RCTUntruncatedMessageKey];
+
+      // Expected resulting exception information:
+      // name: RCTFatalException: <underlying error description>
+      // reason: <underlying error description plus JS stack trace, truncated to 175 characters>
+      // userInfo: <underlying error userinfo, plus untruncated description plus JS stack trace>
+      @throw [[NSException alloc]  initWithName:name reason:message userInfo:userInfo];
 #if DEBUG
     } @catch (NSException *e) {}
 #endif