If JSC fails to load when starting RN, expose that error to the caller

Summary:
See the comments for more info.

Changelog: [Android] [Changed] - Improve exception message when JSC loading fails

Reviewed By: tmikov

Differential Revision: D19917034

fbshipit-source-id: d846f542c31e9c94edcee240c2935d77d48d1f2a

ReactAndroid/src/main/java/com/facebook/react/ReactInstanceManagerBuilder.java

@@ -297,8 +297,34 @@ public class ReactInstanceManagerBuilder {
       SoLoader.loadLibrary("jscexecutor");
       return new JSCExecutorFactory(appName, deviceName);
     } catch (UnsatisfiedLinkError jscE) {
+      // https://github.com/facebook/hermes/issues/78 shows that
+      // people who aren't trying to use Hermes are having issues.
+      // https://github.com/facebook/react-native/issues/25923#issuecomment-554295179
+      // includes the actual JSC error in at least one case.
+      //
+      // So, if "__cxa_bad_typeid" shows up in the jscE exception
+      // message, then we will assume that's the failure and just
+      // throw now.
+
+      if (jscE.getMessage().contains("__cxa_bad_typeid")) {
+        throw jscE;
+      }
+
       // Otherwise use Hermes
-      return new HermesExecutorFactory();
+      try {
+        return new HermesExecutorFactory();
+      } catch (UnsatisfiedLinkError hermesE) {
+        // If we get here, either this is a JSC build, and of course
+        // Hermes failed (since it's not in the APK), or it's a Hermes
+        // build, and Hermes had a problem.
+
+        // We suspect this is a JSC issue (it's the default), so we
+        // will throw that exception, but we will print hermesE first,
+        // since it could be a Hermes issue and we don't want to
+        // swallow that.
+        hermesE.printStackTrace();
+        throw jscE;
+      }
     }
   }
 }