[0.73] Make Hermes the default JS engine

.ado/jobs/cli-init.yml

@@ -51,32 +51,32 @@ parameters:
             platform: x86
             projectType: lib
             additionalRunArguments: --no-autolink --no-deploy
-          - Name: X86DebugCppHermes
+          - Name: X86DebugCppChakra
             language: cpp
             configuration: Debug
             platform: x86
             projectType: app
-            additionalInitArguments: --useHermes
-          - Name: X64ReleaseCsHermes
+            useChakra: true
+          - Name: X64ReleaseCsChakra
             language: cs
             configuration: Release
             platform: x64
             projectType: app
-            additionalInitArguments: --useHermes
+            useChakra: true
             runWack: true
-          - Name: Arm64ReleaseCsHermes
+          - Name: Arm64ReleaseCsChakra
             language: cs
             configuration: Release
             platform: ARM64
             projectType: app
-            additionalInitArguments: --useHermes
+            useChakra: true
             additionalRunArguments: --no-deploy
-          - Name: X64ReleaseCppHermes
+          - Name: X64ReleaseCppChakra
             language: cpp
             configuration: Release
             platform: x64
             projectType: app
-            additionalInitArguments: --useHermes
+            useChakra: true
             runWack: true
           - Name: X86DebugCppNuget
             language: cpp
@@ -224,32 +224,32 @@ parameters:
             platform: x86
             projectType: lib
             additionalRunArguments: --no-autolink --no-deploy
-          - Name: X86DebugCppHermes
+          - Name: X86DebugCppChakra
             language: cpp
             configuration: Debug
             platform: x86
             projectType: app
-            additionalInitArguments: --useHermes
-          - Name: X64ReleaseCsHermes
+            useChakra: true
+          - Name: X64ReleaseCsChakra
             language: cs
             configuration: Release
             platform: x64
             projectType: app
-            additionalInitArguments: --useHermes
+            useChakra: true
             runWack: true
-          - Name: Arm64ReleaseCsHermes
+          - Name: Arm64ReleaseCsChakra
             language: cs
             configuration: Release
             platform: ARM64
             projectType: app
-            additionalInitArguments: --useHermes
+            useChakra: true
             additionalRunArguments: --no-deploy
-          - Name: X64ReleaseCppHermes
+          - Name: X64ReleaseCppChakra
             language: cpp
             configuration: Release
             platform: x64
             projectType: app
-            additionalInitArguments: --useHermes
+            useChakra: true
             runWack: true
           - Name: X86DebugCppNuget
             language: cpp
@@ -410,4 +410,5 @@ jobs:
                   additionalRunArguments: ${{ matrix.additionalRunArguments }}
                   runWack: ${{ coalesce(matrix.runWack, false) }}
                   buildEnvironment: ${{ parameters.buildEnvironment }}
+                  useChakra: ${{ coalesce(matrix.useChakra, false) }} 
                   useNuGet: ${{ coalesce(matrix.useNuGet, false) }}

.ado/jobs/e2e-test.yml

@@ -15,30 +15,30 @@ parameters:
         Matrix:
           - Name: X64Chakra
             BuildPlatform: x64
-            UseHermes: false
+            UseChakra: true
           - Name: X64Hermes
             BuildPlatform: x64
-            UseHermes: true
+            UseChakra: false
           - Name: X86Chakra
             BuildPlatform: x86
-            UseHermes: false
+            UseChakra: true
           - Name: X86Hermes
             BuildPlatform: x86
-            UseHermes: true
+            UseChakra: false
       - BuildEnvironment: Continuous
         Matrix:
           - Name: X64Chakra
             BuildPlatform: x64
-            UseHermes: false
+            UseChakra: true
           - Name: X64Hermes
             BuildPlatform: x64
-            UseHermes: true
+            UseChakra: false
           - Name: X86Chakra
             BuildPlatform: x86
-            UseHermes: false
+            UseChakra: true
           - Name: X86Hermes
             BuildPlatform: x86
-            UseHermes: true
+            UseChakra: false
 
 jobs:
   - ${{ each config in parameters.buildMatrix }}:
@@ -77,7 +77,7 @@ jobs:
               parameters:
                 package: packages/e2e-test-app
                 feature: UseHermes
-                value: ${{ matrix.UseHermes }}
+                value: ${{ not(coalesce(matrix.UseChakra, false)) }}
 
             - template: ../templates/run-windows-with-certificates.yml
               parameters:
@@ -157,7 +157,7 @@ jobs:
   - ${{ each config in parameters.buildMatrix }}:
     - ${{ if eq(config.BuildEnvironment, parameters.buildEnvironment) }}:
       - ${{ each matrix in config.Matrix }}:
-        - ${{ if eq(matrix.UseHermes, true) }}:
+        - ${{ if eq(matrix.UseChakra, false) }}:
           - job: E2ETestFabric${{ matrix.Name }}
             displayName: E2E Test App Fabric ${{ matrix.Name }}
 

.ado/jobs/integration-test.yml

@@ -16,54 +16,64 @@ parameters:
             BuildPlatform: ARM64
             BuildConfiguration: Debug
             DeployOptions: --no-deploy # We don't have Arm agents
-            UseHermes: false
           - Name: X64WebDebug
             BuildPlatform: x64
             BuildConfiguration: Debug
             DeployOptions:
-            UseHermes: false
-          - Name: X64ReleaseHermes
+          - Name: X86WebDebug
+            BuildPlatform: x86
+            BuildConfiguration: Debug
+            DeployOptions:
+          - Name: X64Release
             BuildPlatform: x64
             BuildConfiguration: Release
             DeployOptions:
-            UseHermes: true
-          - Name: X86WebDebug
+          - Name: X86Release
             BuildPlatform: x86
-            BuildConfiguration: Debug
+            BuildConfiguration: Release
+            DeployOptions:
+          - Name: X64ReleaseChakra
+            BuildPlatform: x64
+            BuildConfiguration: Release
             DeployOptions:
-            UseHermes: false
-          - Name: X86ReleaseHermes
+            UseChakra: true
+          - Name: X86ReleaseChakra
             BuildPlatform: x86
             BuildConfiguration: Release
             DeployOptions:
-            UseHermes: true
+            UseChakra: true
       - BuildEnvironment: Continuous
         Matrix:
           - Name: Arm64Debug
             BuildPlatform: ARM64
             BuildConfiguration: Debug
             DeployOptions: --no-deploy # We don't have Arm agents
-            UseHermes: false
           - Name: X64WebDebug
             BuildPlatform: x64
             BuildConfiguration: Debug
             DeployOptions:
-            UseHermes: false
-          - Name: X64ReleaseHermes
+          - Name: X86WebDebug
+            BuildPlatform: x86
+            BuildConfiguration: Debug
+            DeployOptions:
+          - Name: X64Release
             BuildPlatform: x64
             BuildConfiguration: Release
             DeployOptions:
-            UseHermes: true
-          - Name: X86WebDebug
+          - Name: X86Release
             BuildPlatform: x86
-            BuildConfiguration: Debug
+            BuildConfiguration: Release
+            DeployOptions:
+          - Name: X64ReleaseChakra
+            BuildPlatform: x64
+            BuildConfiguration: Release
             DeployOptions:
-            UseHermes: false
-          - Name: X86ReleaseHermes
+            UseChakra: true
+          - Name: X86ReleaseChakra
             BuildPlatform: x86
             BuildConfiguration: Release
             DeployOptions:
-            UseHermes: true
+            UseChakra: true
 
 jobs:
   - ${{ each config in parameters.buildMatrix }}:
@@ -101,7 +111,7 @@ jobs:
               parameters:
                 package: packages/integration-test-app
                 feature: UseHermes
-                value: ${{ matrix.UseHermes }}
+                value: ${{ not(coalesce(matrix.UseChakra, false))}}
 
             - ${{ if eq(matrix.BuildConfiguration, 'Debug') }}:
               # The build is more likely to crash after we've started other bits that

.ado/templates/react-native-init.yml

@@ -24,6 +24,9 @@ parameters:
   - name: additionalRunArguments
     type: string
     default: ''
+  - name: useChakra
+    type: boolean
+    default: false
   - name: useNuGet
     type: boolean
     default: false
@@ -102,6 +105,12 @@ steps:
       workingDirectory: $(Agent.BuildDirectory)\testcli
       env:
         npm_config_registry: http://localhost:4873
+
+  - template:  set-experimental-feature.yml
+    parameters:
+      package: ..\testcli
+      feature: UseHermes
+      value: ${{ not(parameters.UseChakra) }}
 
   - ${{ if eq(parameters.projectType, 'app') }}:
     - powershell: |

change/@react-native-windows-cli-b478dee5-f5a0-4257-96b1-c3cd1ce241f0.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "[0.73] Make Hermes the default JS engine",
+  "packageName": "@react-native-windows/cli",
+  "email": "jthysell@microsoft.com",
+  "dependentChangeType": "patch"
+}

change/react-native-windows-199ec877-3e4a-4205-bdf0-60a698957050.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "[0.73] Make Hermes the default JS engine",
+  "packageName": "react-native-windows",
+  "email": "jthysell@microsoft.com",
+  "dependentChangeType": "patch"
+}

packages/@react-native-windows/cli/src/commands/config/configUtils.ts

@@ -300,6 +300,28 @@ export function tryFindPropertyValue(
   return null;
 }
 
+/**
+ * Search for the given property in the project contents and return its value.
+ * @param projectContents The XML project contents.
+ * @param propertyName The property to look for.
+ * @return The value of the tag if it exists.
+ */
+export function tryFindPropertyValueAsBoolean(
+  projectContents: Node,
+  propertyName: string,
+): boolean | null {
+  const rawValue = tryFindPropertyValue(projectContents, propertyName);
+
+  switch (rawValue) {
+    case 'true':
+      return true;
+    case 'false':
+      return false;
+    default:
+      return null;
+  }
+}
+
 export function findPropertyValue(
   projectContents: Node,
   propertyName: string,

packages/@react-native-windows/cli/src/generator-windows/index.ts

@@ -16,6 +16,7 @@ import findUp from 'find-up';
 import {
   readProjectFile,
   findPropertyValue,
+  tryFindPropertyValueAsBoolean,
 } from '../commands/config/configUtils';
 
 import {
@@ -130,6 +131,27 @@ export async function copyProjectTemplateAndReplace(
     console.log('Using experimental NuGet dependency.');
   }
 
+  const experimentalPropsPath = path.join(
+    destPath,
+    windowsDir,
+    'ExperimentalFeatures.props',
+  );
+
+  let existingUseHermes: boolean | null = null;
+  if (fs.existsSync(experimentalPropsPath)) {
+    existingUseHermes = tryFindPropertyValueAsBoolean(
+      readProjectFile(experimentalPropsPath),
+      'UseHermes',
+    );
+  }
+
+  if (existingUseHermes === false) {
+    console.warn(
+      'Hermes is now the default JS engine and will be enabled for this project. Support for Chakra will be deprecated in the future. To disable Hermes and keep using Chakra for now, see https://microsoft.github.io/react-native-windows/docs/hermes#disabling-hermes.',
+    );
+  }
+  options.useHermes = true;
+
   if (options.useWinUI3) {
     throw new CodedError(
       'IncompatibleOptions',

packages/e2e-test-app/windows/ExperimentalFeatures.props

@@ -2,7 +2,7 @@
 <Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
 
   <PropertyGroup Label="Microsoft.ReactNative Experimental Features">
-    <UseHermes>false</UseHermes>
+    <UseHermes>true</UseHermes>
     <EnableSourceLink>true</EnableSourceLink>
     <ReactExperimentalFeaturesSet>true</ReactExperimentalFeaturesSet>
   </PropertyGroup>

packages/integration-test-app/windows/ExperimentalFeatures.props

@@ -2,7 +2,7 @@
 <Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
 
   <PropertyGroup Label="Microsoft.ReactNative Experimental Features">
-    <UseHermes>false</UseHermes>
+    <UseHermes>true</UseHermes>
     <EnableSourceLink>true</EnableSourceLink>
     <ReactExperimentalFeaturesSet>true</ReactExperimentalFeaturesSet>
   </PropertyGroup>

vnext/Microsoft.ReactNative.IntegrationTests/JsiSimpleTurboModuleTests.js

@@ -6,6 +6,10 @@
  * @format
  */
 
+// Make sure that we import something from react-native so that we build a complete bundle
+// eslint-disable-next-line no-unused-vars
+import {View} from 'react-native';
+
 import {default as myTrivialTurboModule} from './NativeMyTrivialTurboModule';
 
 myTrivialTurboModule.startFromJS();

vnext/Microsoft.ReactNative.IntegrationTests/JsiTurboModuleTests.js

@@ -6,6 +6,10 @@
  * @format
  */
 
+// Make sure that we import something from react-native so that we build a complete bundle
+// eslint-disable-next-line no-unused-vars
+import {View} from 'react-native';
+
 import {default as mySimpleTurboModule} from './NativeMySimpleTurboModuleCxx';
 
 // The logging of the TurboModule functions is verified against the test action sequence.