android: Build RN from source, at our fork, for targetSdkVersion 34

This gets us zulip/react-native@5c36f102f and its fixup commit
zulip/react-native@b7b2f6c22 (on the `0.68.7-zulip` branch), to fix
a build failure with `targetSdkVersion = 34` without having to
upgrade to RN v0.73. (The build failure is in debug builds only, but
we still need to make those to develop fixes in this legacy project
as needed.)

Thanks to Greg for investigating the build failure:
  #5877 (comment)

Since (as part of working on this) the `0.68.7-zulip` branch also
includes the things that were in the patch-package patch, that patch
becomes redundant and we delete it here.

Done by digesting the history of RN's doc on building RN from
source:
  facebook/react-native-website@22da0cc63
and making some simplifications.

The line `ndkVersion = 24…` sets a variable that ReactAndroid reads,
to control the NDK version it builds with. It would otherwise build
with NDK 21, which is old and chosen automatically based on
ReactAndroid's targetSdkVersion of 31. We need it to be at least 24
for Apple Silicon support.

android/app/build.gradle

@@ -240,7 +240,7 @@ dependencies {
 
     implementation fileTree(dir: "libs", include: ["*.jar"])
     //noinspection GradleDynamicVersion
-    implementation "com.facebook.react:react-native:+"  // From node_modules
+    implementation project(':ReactAndroid')
 
     implementation "androidx.swiperefreshlayout:swiperefreshlayout:1.0.0"
 

android/build.gradle

@@ -20,6 +20,9 @@ buildscript {
         // What's the latest?  Consult this list:
         //   https://developer.android.com/studio/releases/platforms
         compileSdkVersion = 34
+
+        // Latest NDK 24, for Apple Silicon compatibility.
+        ndkVersion = "24.0.8215888"
     }
     repositories {
         google()
@@ -61,6 +64,15 @@ allprojects {
         mavenCentral()
         google()
     }
+
+    configurations.all {
+        resolutionStrategy {
+            dependencySubstitution {
+                // Make our dependencies look at our RN fork built from source.
+                substitute module("com.facebook.react:react-native:+") with project(":ReactAndroid")
+            }
+        }
+    }
 }
 
 subprojects {

android/settings.gradle

@@ -1,3 +1,11 @@
+pluginManagement {
+    repositories {
+        gradlePluginPortal()
+        mavenLocal()
+        google()
+    }
+}
+
 rootProject.name = 'ZulipMobile'
 
 apply from: '../node_modules/expo/scripts/autolinking.gradle'
@@ -7,3 +15,11 @@ apply from: file("../node_modules/@react-native-community/cli-platform-android/n
 applyNativeModulesSettingsGradle(settings)
 
 include ':app'
+
+include ':ReactAndroid'
+project(':ReactAndroid').projectDir = new File(
+    rootProject.projectDir, '../node_modules/react-native/ReactAndroid')
+
+// The RN Gradle Plugin is needed to build RN from source.
+// (We do that to make some changes to RN, with our zulip/react-native fork.)
+includeBuild('../node_modules/react-native/packages/react-native-gradle-plugin')

docs/howto/forked-rn.md

@@ -0,0 +1,24 @@
+# Using a `react-native` with cherry-picked or custom changes
+
+Since 2024-09, we use a fork of `react-native` to make changes
+atop 0.68.7. We prefer to avoid upgrading to later `react-native`
+releases because it's laborious and we're eager to retire this
+codebase and transition to `zulip-flutter`.
+
+When there's an issue in React Native that calls for changes in
+React Native:
+
+- Push those changes to our RN fork, `zulip/react-native`,
+  on the `0.68.7-zulip` branch.
+
+- Update the `package.json`:
+
+  ```json
+  "react-native": "zulip/react-native#<commit-id>",
+  ```
+
+- Run `yarn`.
+
+When building for Android, it will take longer the first time because
+React Native is built from source. (`react-native` releases on NPM,
+which we've been using until recently, come with a pre-built binary.)

ios/Podfile.lock

@@ -599,7 +599,7 @@ SPEC CHECKSUMS:
   EXScreenOrientation: e3c072fb0add472a3037482ea43ccbade9b88a25
   EXSQLite: 2b9accd925438293f9f39e0a57a08cca13bdffb2
   FBLazyVector: 63b89dc85804d5817261f56dc4cfb43a9b6d57f5
-  FBReactNativeSpec: 1fa200a9862d9369a53b6fddbbfcdc22bab24062
+  FBReactNativeSpec: de66c1e28c6823a30a53b51dd933560edb24ed3f
   fmt: ff9d55029c625d3757ed641535fd4a75fedc7ce9
   glog: 476ee3e89abb49e07f822b48323c51c57124b572
   RCT-Folly: 4d8508a426467c48885f1151029bc15fa5d7b3b8

package.json

@@ -57,7 +57,7 @@
     "lodash.uniq": "^4.5.0",
     "react": "17.0.2",
     "react-intl": "5.24.6",
-    "react-native": "0.68.7",
+    "react-native": "zulip/react-native#b7b2f6c22",
     "react-native-document-picker": "^8.1.3",
     "react-native-gesture-handler": "^2.8.0",
     "react-native-image-picker": "^5.3.1",