Generate keep.xml to prevent resource shrinking on Android

[jakex7]

Summary:

On Android, when resource shrinking is enabled, all resources added by Metro may be removed as react-native is accessing resources based on strings rather than references, so AGP can't see its usage.

Example output of android/app/build/outputs/mapping/release/resources.txt when shrinkResources is enabled.

@raw/__node_modules_expo_vectoricons_build_vendor_reactnativevectoricons_fonts_materialcommunityicons : reachable=false
@drawable/__common_assets_haptics_icon : reachable=false

It’s a coincidence that most of the resources are currently working, as many file names begin with strings that already exist in the String Pool. For example, node_modules... is flagged as used because 'node' is present in the String Pool, causing it to be whitelisted. However, this does not guarantee that the same will apply to all files - especially in a monorepo setup, where paths are significantly different. For example

• __node_modules_expo_vectoricons_build_vendor_reactnativevectoricons_fonts_materialcommunityicons
• __common_assets_haptics_icon

To prevent that behavior, metro during assets export should create keep.xml listing all resources generated by metro.
https://developer.android.com/build/shrink-code#keep-resources

We have already made a similar change in expo cli: expo/expo#35465

Changelog:

[ANDROID][ADDED] - Generate keep.xml to prevent resource shrinking

Test Plan:

1. Enable resource shrinking in RNTester by adding this to android.buildTypes.release to packages/rn-tester/android/app/build.gradle.kts

isMinifyEnabled = true
isShrinkResources = true

2. Use some resources in playground, for example:

diff --git a/packages/rn-tester/js/examples/Playground/RNTesterPlayground.js b/packages/rn-tester/js/examples/Playground/RNTesterPlayground.js
index 9dbacb99701..9ac9c231f3f 100644
--- a/packages/rn-tester/js/examples/Playground/RNTesterPlayground.js
+++ b/packages/rn-tester/js/examples/Playground/RNTesterPlayground.js
@@ -11,16 +11,14 @@
 
 import type {RNTesterModuleExample} from '../../types/RNTesterTypes';
 
-import RNTesterText from '../../components/RNTesterText';
 import * as React from 'react';
 import {StyleSheet, View} from 'react-native';
+import {Header} from "react-native/Libraries/NewAppScreen";
 
 function Playground() {
   return (
     <View style={styles.container}>
-      <RNTesterText>
-        Edit "RNTesterPlayground.js" to change this file
-      </RNTesterText>
+      <Header />
     </View>
   );
 }

3. Build app using hermesRelease variant
4. See Playground screen

Before	After

5. Inspect packages/rn-tester/android/app/build/outputs/mapping/hermesRelease/resources.txt

Before	After
@drawable/_reactnative_libraries_newappscreen_components_logo : reachable=false	@drawable/_reactnative_libraries_newappscreen_components_logo : reachable=true

[cortinico]

@robhogan @huntie can you take this one? I can help on the Android side of things if needed

[facebook-github-bot]

@huntie has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[facebook-github-bot]

@huntie merged this pull request in 864833f.

[react-native-bot]

This pull request was successfully merged by @jakex7 in 864833f

^{When will my fix make it into a release? | How to file a pick request?}