Flutter release builds (via flutter build apk --release) aren't optimized #136879
Description
It seems flutter release builds result in APKs that have dex in them (from java/kotlin) that wasn't optimized.
This can be seen as follows:
% flutter create hello && cd hello
### Build the APK
hello % flutter build apk --release
### Examine the R8/Proguard rules used for tree shaking
hello % cat build/app/outputs/mapping/release/configuration.txt
...
# Optimization is turned off by default. ...
-dontoptimize
...
### Examine size of resulting DEX bytecode
hello % unzip -l build/app/outputs/flutter-apk/app-release.apk | grep classes.dex
689484 1981-01-01 01:01 classes.dex
The root cause is that flutter's gradle file explicitly tells the R8 to use unoptimized android proguard rules.
If we fix this via:
diff --git a/packages/flutter_tools/gradle/src/main/groovy/flutter.groovy b/packages/flutter_tools/gradle/src/main/groovy/flutter.groovy
index f3c1a4145c..f5950024e2 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"
}
}
}and rebuild we get the following:
hello % flutter build apk --release
hello % unzip -l build/app/outputs/flutter-apk/app-release.apk | grep classes.dex
512376 1981-01-01 01:01 classes.dex
=> The classes.dex file shrinks by 25% (689484 -> 512376).
=> Bigger apps that use various java/kotlin plugins may benefit quite significantly (compared with the hello world)
/cc @reidbaker