android build: Prepare to activate Hermes.

See #4131, the issue for activating Hermes.

Part of the RN v0.59 -> v0.60 upgrade [1]. This must happen at or
after the upgrade commit because the use of Hermes is newly
supported.

RN did this in two parts. First, and released in RN v0.60.0, they
started using NPM to manage the JSC version.

This part corresponds to

- facebook/react-native@8e375850d
- facebook/react-native@4bb0b4f20 (a partial reversion)

Then:

- In 0.60.1, facebook/react-native@e857d7066 was released,
  giving Hermes support.
- In 0.60.2, facebook/react-native@0738fe573 was released,
  fixing an error in the template app.

[1]: https://react-native-community.github.io/upgrade-helper/?from=0.59.10&to=0.60.6

android/app/build.gradle

@@ -81,6 +81,7 @@ import com.android.build.OutputFile
 
 project.ext.react = [
     entryFile: "index.js",
+    enableHermes: false, // clean and rebuild if changing
     // quasi-unstable: see commits 8f8a266af and 833d083a9
     jsBundleDirRelease: "$buildDir/intermediates/merged_assets/release/out"
 ]
@@ -120,6 +121,28 @@ def enableSeparateBuildPerCPUArchitecture = false
 def enableProguardInReleaseBuilds = false
 def shrinkResourcesInProguardBuilds = false
 
+/**
+  * The preferred build flavor of JavaScriptCore.
+  *
+  * For example, to use the international variant, you can use:
+  * `def jscFlavor = 'org.webkit:android-jsc-intl:+'`
+  *
+  * The international variant includes ICU i18n library and necessary data
+  * allowing to use e.g. `Date.toLocaleString` and `String.localeCompare` that
+  * give correct results when using with locales other than en-US.  Note that
+  * this variant is about 6MiB larger per architecture than default.
+ */
+def jscFlavor = 'org.webkit:android-jsc:+'
+
+/**
+ * Whether to enable the Hermes VM.
+ *
+ * This should be set on project.ext.react and mirrored here.  If it is not set
+ * on project.ext.react, JavaScript will not be compiled to Hermes Bytecode
+ * and the benefits of using Hermes will therefore be sharply reduced.
+ */
+def enableHermes = project.ext.react.get("enableHermes", false);
+
 android {
     defaultConfig {
         applicationId "com.zulipmobile"
@@ -191,6 +214,15 @@ android {
             }
         }
     }
+
+    packagingOptions {
+        pickFirst '**/armeabi-v7a/libc++_shared.so'
+        pickFirst '**/x86/libc++_shared.so'
+        pickFirst '**/arm64-v8a/libc++_shared.so'
+        pickFirst '**/x86_64/libc++_shared.so'
+        pickFirst '**/x86/libjsc.so'
+        pickFirst '**/armeabi-v7a/libjsc.so'
+    }
 }
 
 repositories {
@@ -217,6 +249,15 @@ dependencies {
     implementation "com.google.firebase:firebase-messaging:17.3.4"
     implementation "me.leolin:ShortcutBadger:1.1.16@aar"
     implementation "com.facebook.react:react-native:+"  // From node_modules
+
+    if (enableHermes) {
+      def hermesPath = "../../node_modules/hermesvm/android/";
+      debugImplementation files(hermesPath + "hermes-debug.aar")
+      releaseImplementation files(hermesPath + "hermes-release.aar")
+    } else {
+      implementation jscFlavor
+    }
+
     implementation 'com.facebook.fresco:animated-gif:1.10.0' // For animated GIF support
     implementation 'androidx.browser:browser:1.0.0'
     addUnimodulesDependencies()

android/app/src/main/java/com/zulipmobile/MainApplication.java

@@ -1,6 +1,10 @@
 package com.zulipmobile;
 
 import android.app.Application;
+import android.util.Log;
+
+import com.facebook.hermes.reactexecutor.HermesExecutorFactory;
+import com.facebook.react.bridge.JavaScriptExecutorFactory;
 import com.RNFetchBlob.RNFetchBlobPackage;
 import com.facebook.react.ReactApplication;
 import com.facebook.react.ReactNativeHost;

android/build.gradle

@@ -38,12 +38,17 @@ buildscript {
 allprojects {
     repositories {
         mavenLocal()
-        google()
-        jcenter()
         maven {
             // All of React Native (JS, Obj-C sources, Android binaries) is installed from npm
             url "$rootDir/../node_modules/react-native/android"
         }
+        maven {
+            // Android JSC is installed from npm
+            url("$rootDir/../node_modules/jsc-android/dist")
+        }
+
+        google()
+        jcenter()
     }
 }