React Native 0.64 won't build iOS app after updating Xcode to 12.5 and iOS to 14.5

There's a solution I found here.

Add this to your post_install in your Podfile:

post_install do |installer|  flipper_post_install(installer)  ## Fix for Flipper-Folly on iOS 14.5  find_and_replace("Pods/Flipper-Folly/folly/synchronization/DistributedMutex-inl.h",    "atomic_notify_one(state)", "folly::atomic_notify_one(state)")  find_and_replace("Pods/Flipper-Folly/folly/synchronization/DistributedMutex-inl.h",    "atomic_wait_until(&state, previous | data, deadline)", "folly::atomic_wait_until(&state, previous | data, deadline)")end

You'll also need to add the function def for this find_and_replace function (you can put this function anywhere in the podfile):

def find_and_replace(dir, findstr, replacestr)  Dir[dir].each do |name|      text = File.read(name)      replace = text.gsub(findstr,replacestr)      if text != replace          puts "Fix: " + name          File.open(name, "w") { |file| file.puts replace }          STDOUT.flush      end  end  Dir[dir + '*/'].each(&method(:find_and_replace))end

Run pod install again and it should work. If you get an error relating to permissions while accessing the DistributedMutex-inl.h file, delete your /pods folder and run pod install again

You should see text print out that says Fix: Pods/Flipper-Folly/folly/synchronization/DistributedMutex-inl.h, etc. If you don't, double check the path in the find_and_replace call.

There is an open RN issue here: https://github.com/facebook/react-native/issues/31179

For me commenting out Flipper in the Podfile, pod install, and rebuild worked as a temp solution.

  # Enables Flipper.  #  # Note that if you have use_frameworks! enabled, Flipper will not work and  # you should disable these next few lines.  # use_flipper!  # post_install do |installer|  #   flipper_post_install(installer)  # end

Solution without losing Flipper functionality:

Define the upgraded dependencies for Flipper in the Podfile

React Native 62

def add_flipper_pods!(versions = {})  versions['Flipper'] ||= '~> 0.87.0' 👈  versions['DoubleConversion'] ||= '1.1.7'  versions['Flipper-Folly'] ||= '~> 2.5.3' 👈  versions['Flipper-Glog'] ||= '0.3.6'  versions['Flipper-PeerTalk'] ||= '~> 0.0.4'  versions['Flipper-RSocket'] ||= '~> 1.3.1' 👈

React Native 63

# Enables Flipper.  #  # Note that if you have use_frameworks! enabled, Flipper will not work and  # you should disable these next few lines.  use_flipper!({'Flipper' => '0.87.0' 👈, 'Flipper-Folly' => '2.5.3' 👈, 'Flipper-RSocket' => '1.3.1' 👈})  post_install do |installer|    flipper_post_install(installer)  end

cd ios && pod install and you should be good to go

React Native 64

Bump the version to 0.64.1 in the package.json

yarn install && pod install --repo-update && react-native run-ios

https://github.com/facebook/react-native/releases/tag/v0.64.1