How to Tackle Proguard/R8 Code Decay in Android Apps – A Practical Guide

Engineering decay is a subtle yet painful issue that appears during app iteration, affecting development efficiency, product quality, stability, APK size and performance. Unlike a one‑time fix, it requires continuous, sustainable governance.

Basic Knowledge

In Android (Java) development, “code Proguard” refers to using the Proguard tool to shrink, optimize and obfuscate Java code, removing dead code, improving logic and shortening symbols. Google now replaces Proguard with the self‑developed R8 in recent Android Gradle Plugin versions, but the term still denotes the processing steps.

Function Introduction

Shrink : static analysis of code references to delete unused classes, fields, methods and resources, reducing APK size.

Optimize : deep analysis of execution logic to remove dead branches, inline methods, and apply dozens of optimizations, decreasing runtime method execution time.

Obfuscate : shorten class, field and method names to further shrink the APK and raise the difficulty of reverse engineering.

A typical processing flow alternates shrink and optimize, possibly looping multiple times (R8 does not allow configuring loop count).

Configuration Items

Proguard offers powerful configuration options, divided into global configurations and keep configurations. R8 disables many global options for consistency.

Global Configuration

Shrink configuration : e.g., -dontshrink disables shrinking; -whyareyoukeeping explains why a class is kept.

# Example: class TestProguardMethodOnly is kept directly by a keep rule
# Proguard result shows the shortest path
com.example.myapplication.proguard.TestProguardMethodOnly
  is kept by a directive in the configuration.

Keep Configuration

Keep rules specify classes, fields or methods that must not be removed or obfuscated. Types include:

Direct keep: -keep (no shrink, no obfuscate).

Keep names: -keepnames (allow shrinking, no obfuscate).

Keep class members: -keepclassmembers (no shrink, no obfuscate for members).

Conditional keep: -keepclasseswithmembers, -keepclasseswithmembernames, etc.

# Sample keep rule
-keep class com.example.myapplication.proguard.TestProguardFieldOnly { *; }

Tool Selection

Android developers can choose between Proguard and R8. R8 offers faster processing and better results, with two modes:

Normal mode – compatible with Proguard.

Full mode – more aggressive optimizations; enable via android.enableR8.fullMode=true in gradle.properties.

Custom Configuration

Custom rules are added per module. The source of each keep rule can be traced, and tools can detect which modules contribute which rules.

# Project:app:1.0
|-- -keepclasseswithmembers class com.example.myapplication.proguard.** { *; }
|-- -keepclassmembers class com.example.myapplication.proguard.** { *; }
|-- -keep class com.example.libraryaar1.CustomImageView { <init>(...); }

Governance Practice

Two main problems arise over time:

Global configuration changes unintentionally affect stability, size and performance.

Keep rules accumulate, increasing build time and APK size.

Detection tools were built to:

List keep rules per module.

Show which classes are hit by each keep rule.

Identify unused keep rules.

* -keep class com.youku.android.widget.TextSetView { <init>(...); }
|-- com.youku.android:moduleOne:1.21.407.6
    |-- com.youku.android.widget.TextSetView

Analysis, processing and verification steps differ for unused, redundant and over‑retained rules, with verification relying on generated usage.txt, mapping.txt and seeds.txt files.

Governance Panorama

After cleaning 20% of keep rules (758 out of 3812), build time for Proguard decreased by 18%. Future work includes centralizing keep rule management, white‑listing necessary rules, and gradually eliminating redundant and over‑retained rules.

What Else Can Be Done

Further research will target detection of redundant and over‑retained keep rules, and systematic cleanup of legacy keep configurations.

References

Proguard official documentation: https://www.guardsquare.com/manual/configuration/usage

R8 official documentation: https://developer.android.com/studio/build/shrink-code

consumerProguardFiles documentation: https://developer.android.com/studio/projects/android-library.html#Considerations