From 1dd21f8d996f233ed0b8aeb8451d16d9df783f39 Mon Sep 17 00:00:00 2001
From: Martin Kustermann <kustermann@google.com>
Date: Fri, 27 Oct 2023 09:51:47 +0200
Subject: [PATCH] Ensure `flutter build apk --release` optimizes+shrinks
 platform code (#136880)

Since the original PR that supposedly enabled proguard, it was using the
android proguard rules that disable optimizations. See initial PR in [0]

This PR changes the flutter gradle plugin to use the
`proguard-android-optimize.txt` (instead of `proguard-android.txt`)
which will enable optimizations/shrinking of platform code (i.e.
java/kotlin).

For a simple flutter hello world this results in a 25% reduction in the
resulting DEX file (`classes.dex` of the APK).

Note for users:

For some users this may result in issues because their java/kotlin code is
now better optimized & tree shaken and thereby symbols may be no longer
available or being obfuscated.

To fix those issues it's best to craft precise proguard rules describing the
extra symbols that are needed by the app (see [1]). But it's also possible to
opt out entirely of optimizations by using the unoptimized proguard rules.

To add custom proguard rules or use the unoptimized android rules, one can
update `android/app/build.gradle`:
```
android {
    ...
    buildTypes {
        release {
            ...
+            proguardFiles(
+                // Not ideal: Disables optimizations by using unoptimized android rules.
+                getDefaultProguardFile("proguard-android.txt"),
+
+                // Better: Have precise keep rules to only keep things that are needed.
+                "custom-rules.pro",
+            )
        }
    }
}
```


[0] f098de1fdedec2232aa740a6413f318166762795
[1] https://developer.android.com/build/shrink-code

Fixes https://github.com/flutter/flutter/issues/136879
---
 packages/flutter_tools/gradle/src/main/groovy/flutter.groovy | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/flutter_tools/gradle/src/main/groovy/flutter.groovy b/packages/flutter_tools/gradle/src/main/groovy/flutter.groovy
index ff5b509896f..7c6b483ed4d 100644
--- a/packages/flutter_tools/gradle/src/main/groovy/flutter.groovy
+++ b/packages/flutter_tools/gradle/src/main/groovy/flutter.groovy
@@ -308,7 +308,7 @@ class FlutterPlugin implements Plugin<Project> {
                     shrinkResources isBuiltAsApp(project)
                     // Fallback to `android/app/proguard-rules.pro`.
                     // This way, custom Proguard rules can be configured as needed.
-                    proguardFiles project.android.getDefaultProguardFile("proguard-android.txt"), flutterProguardRules, "proguard-rules.pro"
+                    proguardFiles project.android.getDefaultProguardFile("proguard-android-optimize.txt"), flutterProguardRules, "proguard-rules.pro"
                 }
             }
         }