Saad Najmi
b04d17afca
Summary: Originally with https://github.com/facebook/react-native/commit/5cf8f43ab182781ea82e88077df425c3efbfc21f , we added a call to a new Apple API `JSGlobalContextSetInspectable` to ensure that our Javascript running with JSC is debuggable. That change was guarded with a `__builtin_available(macOS 13.3, iOS 16.4, tvOS 16.4, *)` check to make sure it only ran on OS'es where to function existed. Later, in https://github.com/facebook/react-native/commit/3eeee11d7ac4075d0917233d3be4a9469f802d35 we did an extra guard in the way of a macro to check we were compiling against a new enough version of Xcode (so that Xcode knows about the symbol). Between the runtime check and the compile time check, we should be good right? Wrong! As it turns out, this bit of code still caused crashes on iOS 15 devices (See this [Apple Forum Thread](https://forums.developer.apple.com/forums/thread/749534)). To address this, https://github.com/facebook/react-native/pull/44185 was added which added a new compiler guard (`__OSX_AVAILABLE_STARTING(MAC_NA, IPHONE_16_4)` was added. Unfortunately, this guard is incorrect: It is basically checking if our minimum iOS deployment target is 16.4 (It's not, as of writing it is iOS 13.4), which effectively means this code is never compiled and one can never direct debug with JSC on iOS 16.4+ 😨! So what went wrong, and why were the first two guards not good enough? Three main reasons.. Firstly, this is a device only crash, and not reproducible on simulator. This is probably why the crash was not caught earlier. Secondly, It's because system frameworks (like JavascriptCore) are _dynamically_ linked: the linker doesn't look for the symbol till runtime (and crashes when doing so). Thirdly, It's because we are _strongly_ linking the framework, so every symbol must be present and the macros / guard Apple provides with `AvailabilityMacros.h` don't work. What we want to do is link JavascriptCore as a `weak_framework`, more info here: https://developer.apple.com/library/archive/documentation/MacOSX/Conceptual/BPFrameworks/Concepts/WeakLinking.html From that link: > One challenge faced by developers is that of taking advantage of new features introduced in new versions of OS X while still supporting older versions of the system. Normally, if an application uses a new feature in a framework, it is unable to run on earlier versions of the framework that do not support that feature. Such applications would either fail to launch or crash when an attempt to use the feature was made. Apple has solved this problem by adding support for weakly-linked symbols. >When a symbol in a framework is defined as weakly linked, the symbol does not have to be present at runtime for a process to continue running. The static linker identifies a weakly linked symbol as such in any code module that references the symbol. The dynamic linker uses this same information at runtime to determine whether a process can continue running. If a weakly linked symbol is not present in the framework, the code module can continue to run as long as it does not reference the symbol. However, if the symbol is present, the code can use it normally. This seems to be exactly what we want, and the Apple provided method for using new APIs in system frameworks! Let's update our podspecs so we link JavascriptCore weakly. As a bonus (and admittedly, the original purpose of this PR) let's add macOS support to the `JSC_HAS_INSPECTABLE` macro (This file `JSCRuntime.cpp` used to have more explicit macOS support in it's macros, but I had removed it with https://github.com/facebook/react-native/commit/fb30fcaa2f526cc1f7c2d4189ec9c57f9cf9b3c5). ## Changelog: [IOS] [FIXED] - Fix Direct Debugging with JSC Pull Request resolved: https://github.com/facebook/react-native/pull/39549 Test Plan: Tested that RNTester doesn't crash on boot running on an iPad Air 2 running iOS 15.8., and that an iOS 17.2 simulator is debuggable. Built RN-Tester and RN-Tester-macOS and verified both show up in Safari Web Inspectors' debug menu: <img width="1316" alt="Screenshot 2023-09-19 at 10 48 43 PM" src="https://github.com/facebook/react-native/assets/6722175/c642e6e0-36af-4c9f-845a-7e491489f419"> macOS screenshot small bc I got some internal stuff I gotta crop 😅 <img width="347" alt="Screenshot 2023-09-19 at 10 53 46 PM" src="https://github.com/facebook/react-native/assets/6722175/1e802c88-02b8-49e1-8fd2-d91726ca1e93"> Reviewed By: huntie Differential Revision: D67338150 Pulled By: cipolleschi fbshipit-source-id: 620c3b3cc1e37e54de7fa4dc9956a02c8f3c09f8
React Native
Learn once, write anywhere:
Build mobile apps with React.
Getting Started · Learn the Basics · Showcase · Contribute · Community · Support
React Native brings React's declarative UI framework to iOS and Android. With React Native, you use native UI controls and have full access to the native platform.
- Declarative. React makes it painless to create interactive UIs. Declarative views make your code more predictable and easier to debug.
- Component-Based. Build encapsulated components that manage their state, then compose them to make complex UIs.
- Developer Velocity. See local changes in seconds. Changes to JavaScript code can be live reloaded without rebuilding the native app.
- Portability. Reuse code across iOS, Android, and other platforms.
React Native is developed and supported by many companies and individual core contributors. Find out more in our ecosystem overview.
Contents
- Requirements
- Building your first React Native app
- Documentation
- Upgrading
- How to Contribute
- Code of Conduct
- License
📋 Requirements
React Native apps may target iOS 15.1 and Android 7.0 (API 24) or newer. You may use Windows, macOS, or Linux as your development operating system, though building and running iOS apps is limited to macOS. Tools like Expo can be used to work around this.
🎉 Building your first React Native app
Follow the Getting Started guide. The recommended way to install React Native depends on your project. Here you can find short guides for the most common scenarios:
📖 Documentation
The full documentation for React Native can be found on our website.
The React Native documentation discusses components, APIs, and topics that are specific to React Native. For further documentation on the React API that is shared between React Native and React DOM, refer to the React documentation.
The source for the React Native documentation and website is hosted on a separate repository, @facebook/react-native-website.
🚀 Upgrading
Upgrading to new versions of React Native may give you access to more APIs, views, developer tools, and other goodies. See the Upgrading Guide for instructions.
React Native releases are discussed in this discussion repo.
👏 How to Contribute
The main purpose of this repository is to continue evolving React Native core. We want to make contributing to this project as easy and transparent as possible, and we are grateful to the community for contributing bug fixes and improvements. Read below to learn how you can take part in improving React Native.
Code of Conduct
Facebook has adopted a Code of Conduct that we expect project participants to adhere to. Please read the full text so that you can understand what actions will and will not be tolerated.
Contributing Guide
Read our Contributing Guide to learn about our development process, how to propose bugfixes and improvements, and how to build and test your changes to React Native.
Open Source Roadmap
You can learn more about our vision for React Native in the Roadmap.
Good First Issues
We have a list of good first issues that contain bugs which have a relatively limited scope. This is a great place to get started, gain experience, and get familiar with our contribution process.
Discussions
Larger discussions and proposals are discussed in @react-native-community/discussions-and-proposals.
📄 License
React Native is MIT licensed, as found in the LICENSE file.
React Native documentation is Creative Commons licensed, as found in the LICENSE-docs file.