Update getDefaultJSExecutorFactory to load Hermes first and fallback …

…to JSC (#41914)

Summary:
Pull Request resolved: #41914

If the user does not specify which engine they're using, we still default to loading JSC first and then attempting to load Hermes.
This has a small performance hit (as we attempt to load an existing library) + it prints an inactionable log for the user every time.

Changelog:
[Android] [Fixed] - Update getDefaultJSExecutorFactory to load Hermes first and fallback to JSC

Reviewed By: luluwu2032

Differential Revision: D52080545

fbshipit-source-id: 95f37304d713da7d7079eabbd2dfdf230d29a1b9

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/ReactInstanceManagerBuilder.java

@@ -373,31 +373,28 @@ public ReactInstanceManager build() {
   private JavaScriptExecutorFactory getDefaultJSExecutorFactory(
       String appName, String deviceName, Context applicationContext) {
 
-    // Relying solely on try catch block and loading jsc even when
-    // project is using hermes can lead to launch-time crashes especially in
-    // monorepo architectures and hybrid apps using both native android
-    // and react native.
-    // So we can use the value of enableHermes received by the constructor
-    // to decide which library to load at launch
-
-    // if nothing is specified, use old loading method
-    // else load the required engine
+    initializeSoLoaderIfNecessary(applicationContext);
+    // Hermes has been enabled by default in OSS since React Native 0.70.
+    // If the user hasn't specified a JSEngineResolutionAlgorithm,
+    // we attempt to load Hermes first, and fallback to JSC if we can't resolve the library.
     if (mJSEngineResolutionAlgorithm == null) {
-      FLog.w(
-          TAG,
-          "You're not setting the JS Engine Resolution Algorithm. "
-              + "We'll try to load JSC first, and if it fails we'll fallback to Hermes");
       try {
-        // If JSC is included, use it as normal
-        initializeSoLoaderIfNecessary(applicationContext);
-        JSCExecutor.loadLibrary();
-        return new JSCExecutorFactory(appName, deviceName);
-      } catch (UnsatisfiedLinkError jscE) {
-        if (jscE.getMessage().contains("__cxa_bad_typeid")) {
-          throw jscE;
-        }
         HermesExecutor.loadLibrary();
         return new HermesExecutorFactory();
+      } catch (UnsatisfiedLinkError ignoredHermesError) {
+        try {
+          JSCExecutor.loadLibrary();
+          return new JSCExecutorFactory(appName, deviceName);
+        } catch (UnsatisfiedLinkError jscError) {
+          FLog.e(
+              TAG,
+              "Unable to load neither the Hermes nor the JSC native library. "
+                  + "Your application is not built correctly and will fail to execute");
+          if (jscError.getMessage().contains("__cxa_bad_typeid")) {
+            throw jscError;
+          }
+          return null;
+        }
       }
     } else if (mJSEngineResolutionAlgorithm == JSEngineResolutionAlgorithm.HERMES) {
       HermesExecutor.loadLibrary();