Make Hermes the default engine on iOS (#34085)

Summary:
Pull Request resolved: #34085

Hermes is now the default engine on iOS.

Apps can choose to continue using JSC by setting `hermes_enabled` to `false` in their Podfile.

The RNTester app now uses Hermes, as well. Use JSC in RNTester by setting `USE_HERMES=0` when running `pod install`.

Changelog:

[iOS][Changed] Hermes is now the default engine on iOS. This setting is controlled via `flags[:hermes_enabled]` in the Podfile.

Reviewed By: cortinico, cipolleschi

Differential Revision: D37361468

fbshipit-source-id: e6dda6a23eea4a824ad157d1a26f17e181db33cd

packages/rn-tester/Podfile

@@ -21,7 +21,9 @@ def pods(options = {}, use_flipper: false)
   project 'RNTesterPods.xcodeproj'
 
   fabric_enabled = true
-  hermes_enabled = ENV['USE_HERMES'] == '1'
+  # Hermes is now enabled by default.
+  # The following line will only disable Hermes if the USE_HERMES envvar is SET to a value other than 1 (e.g. USE_HERMES=0).
+  hermes_enabled = !ENV.has_key?('USE_HERMES') || ENV['USE_HERMES'] == '1'
   puts "Building RNTester with Fabric #{fabric_enabled ? "enabled" : "disabled"}.#{hermes_enabled ? " Using Hermes engine." : ""}"
 
   if ENV['RCT_NEW_ARCH_ENABLED'] == '1'

packages/rn-tester/README.md

@@ -30,7 +30,7 @@ If you are still having a problem after doing the clean up (which can happen if
 Both macOS and Xcode are required.
 1. `cd packages/rn-tester`
 1. Install [Bundler](https://bundler.io/): `gem install bundler`. We use bundler to install the right version of [CocoaPods](https://cocoapods.org/) locally.
-1. Install Bundler and CocoaPods dependencies: `bundle install && bundle exec pod install` or `yarn setup-ios-jsc`. In order to use Hermes engine instead of JSC, run: `USE_HERMES=1 bundle exec pod install` or `yarn setup-ios-hermes` instead.
+1. Install Bundler and CocoaPods dependencies: `bundle install && bundle exec pod install` or `yarn setup-ios-hermes`. In order to use JSC instead of Hermes engine, run: `USE_HERMES=0 bundle exec pod install` or `yarn setup-ios-jsc` instead.
 1. Open the generated `RNTesterPods.xcworkspace`. This is not checked in, as it is generated by CocoaPods. Do not open `RNTesterPods.xcodeproj` directly.
 
 #### Note for M1 users

packages/rn-tester/package.json

@@ -14,7 +14,7 @@
     "install-android-jsc": "../../gradlew :packages:rn-tester:android:app:installJscDebug",
     "install-android-hermes": "../../gradlew :packages:rn-tester:android:app:installHermesDebug",
     "clean-android": "rm -rf android/app/build",
-    "setup-ios-jsc": "bundle install && bundle exec pod install",
+    "setup-ios-jsc": "bundle install && USE_HERMES=0 bundle exec pod install",
     "setup-ios-hermes": "bundle install && USE_HERMES=1 bundle exec pod install",
     "clean-ios": "rm -rf build/generated/ios && rm -rf Pods && rm Podfile.lock"
   },

scripts/cocoapods/__tests__/utils-test.rb

@@ -17,7 +17,7 @@ def teardown
         SysctlChecker.reset()
         Environment.reset()
         ENV['RCT_NEW_ARCH_ENABLED'] = '0'
-        ENV['USE_HERMES'] = '0'
+        ENV['USE_HERMES'] = '1'
     end
 
     # ======================= #
@@ -75,30 +75,30 @@ def test_warnIfNotOnArm64_whenSysctlReturns1AndRubyNotIncludeArm64_warns
     def test_getDefaultFlag_whenOldArchitecture()
         # Arrange
         ENV['RCT_NEW_ARCH_ENABLED'] = '0'
-        ENV['USE_HERMES'] = '0'
+
         # Act
         flags = ReactNativePodsUtils.get_default_flags()
 
         # Assert
         assert_equal(flags, {
             :fabric_enabled => false,
-            :hermes_enabled => false,
+            :hermes_enabled => true,
             :flipper_configuration => FlipperConfiguration.disabled
         })
     end
 
-    def test_getDefaultFlag_whenOldArchitectureButHermesEnabled()
+    def test_getDefaultFlag_whenOldArchitectureButHermesDisabled()
         # Arrange
         ENV['RCT_NEW_ARCH_ENABLED'] = '0'
-        ENV['USE_HERMES'] = '1'
+        ENV['USE_HERMES'] = '0'
 
         # Act
         flags = ReactNativePodsUtils.get_default_flags()
 
         # Assert
         assert_equal(flags, {
             :fabric_enabled => false,
-            :hermes_enabled => true,
+            :hermes_enabled => false,
             :flipper_configuration => FlipperConfiguration.disabled
         })
     end
@@ -118,6 +118,22 @@ def test_getDefaultFlag_whenNewArchitecture()
         })
     end
 
+    def test_getDefaultFlag_whenNewArchitectureButHermesDisabled()
+        # Arrange
+        ENV['RCT_NEW_ARCH_ENABLED'] = '1'
+        ENV['USE_HERMES'] = '0'
+
+        # Act
+        flags = ReactNativePodsUtils.get_default_flags()
+
+        # Assert
+        assert_equal(flags, {
+            :fabric_enabled => true,
+            :hermes_enabled => false,
+            :flipper_configuration => FlipperConfiguration.disabled
+        })
+    end
+
     # ============== #
     # TEST - has_pod #
     # ============== #

scripts/cocoapods/utils.rb

@@ -19,7 +19,7 @@ def self.warn_if_not_on_arm64
     def self.get_default_flags
         flags = {
             :fabric_enabled => false,
-            :hermes_enabled => false,
+            :hermes_enabled => true,
             :flipper_configuration => FlipperConfiguration.disabled
         }
 
@@ -28,8 +28,8 @@ def self.get_default_flags
             flags[:hermes_enabled] = true
         end
 
-        if ENV['USE_HERMES'] == '1'
-            flags[:hermes_enabled] = true
+        if ENV['USE_HERMES'] == '0'
+            flags[:hermes_enabled] = false
         end
 
         return flags

scripts/react-native-xcode.sh

@@ -78,16 +78,15 @@ fi
 # shellcheck source=/dev/null
 source "$REACT_NATIVE_DIR/scripts/node-binary.sh"
 
-[ -z "$HERMES_CLI_PATH" ] && HERMES_CLI_PATH="$PODS_ROOT/hermes-engine/destroot/bin/hermesc"
-
-if [[ -z "$USE_HERMES" && -f "$HERMES_CLI_PATH" ]]; then
-  echo "Enabling Hermes byte-code compilation. Disable with USE_HERMES=false if needed."
-  USE_HERMES=true
-fi
-
-if [[ $USE_HERMES == true && ! -f "$HERMES_CLI_PATH" ]]; then
-  echo "error: USE_HERMES is set to true but the hermesc binary could not be " \
-       "found at ${HERMES_CLI_PATH}. Perhaps you need to run 'bundle exec pod install' or otherwise " \
+HERMES_ENGINE_PATH="$PODS_ROOT/hermes-engine"
+[ -z "$HERMES_CLI_PATH" ] && HERMES_CLI_PATH="$HERMES_ENGINE_PATH/destroot/bin/hermesc"
+
+# Hermes is enabled in new projects by default, so we cannot assume that USE_HERMES=1 is set as an envvar.
+# If hermes-engine is found in Pods, we can assume Hermes has not been disabled.
+# If hermesc is not available and USE_HERMES is either unset or true, show error.
+if [[  -f "$HERMES_ENGINE_PATH" && ! -f "$HERMES_CLI_PATH" ]]; then
+  echo "error: Hermes is enabled but the hermesc binary could not be found at ${HERMES_CLI_PATH}." \
+       "Perhaps you need to run 'bundle exec pod install' or otherwise " \
        "point the HERMES_CLI_PATH variable to your custom location." >&2
   exit 2
 fi
@@ -179,4 +178,4 @@ if [[ $DEV != true && ! -f "$BUNDLE_FILE" ]]; then
   echo "error: File $BUNDLE_FILE does not exist. This must be a bug with" >&2
   echo "React Native, please report it here: https://github.com/facebook/react-native/issues"
   exit 2
-fi
+fi

scripts/react_native_pods.rb

@@ -36,7 +36,7 @@ def use_react_native! (options={})
   production = options[:production] ||= false
 
   # Include Hermes dependencies
-  hermes_enabled = options[:hermes_enabled] ||= false
+  hermes_enabled = options[:hermes_enabled] ||= true
 
   flipper_configuration = options[:flipper_configuration] ||= FlipperConfiguration.disabled
 

scripts/test-manual-e2e.sh

@@ -91,7 +91,7 @@ test_ios_jsc(){
     success "About to test iOS JSC... "
     success "Installing CocoaPods dependencies..."
     rm -rf packages/rn-tester/Pods
-    (cd packages/rn-tester && bundle exec pod install)
+    (cd packages/rn-tester && USE_HERMES=0 bundle exec pod install)
 
     info "Press any key to open the workspace in Xcode, then build and test manually."
     info ""
@@ -232,4 +232,3 @@ init(){
 }
 
 init
-

template/ios/Podfile

@@ -12,9 +12,10 @@ target 'HelloWorld' do
 
   use_react_native!(
     :path => config[:reactNativePath],
-    # By default, Hermes is disabled on Old Architecture, and enabled on New Architecture.
-    # You can enabled/disable it manually by replacing `flags[:hermes_enabled]` with `true` or `false`.
-    :hermes_enabled => flags[:hermes_enabled],
+    # Hermes is now enabled by default. Disable by setting this flag to false.
+    # Upcoming versions of React Native may rely on get_default_flags(), but
+    # we make it explicit here to aid in the React Native upgrade process.
+    :hermes_enabled => true,
     :fabric_enabled => flags[:fabric_enabled],
     # Enables Flipper.
     #