r8-shrink-pro

name	r8-shrink-pro
description	Reviews Android R8 / ProGuard configuration for code-shrinking, optimization, and obfuscation. Covers `-keep` rule discipline, library `consumer-rules.pro` discipline, common reflection-using library rules (Moshi, Room, Hilt, Retrofit, Glide), mapping-file workflow, debugging release-build crashes. Use when reading, writing, or reviewing ProGuard/R8 configuration files.
license	MIT
metadata	{"author":"AppBootstrapAI contributors","version":"1.0","grounded_in":"Android Developers — Shrink, obfuscate, and optimize your app (https://developer.android.com/build/shrink-code), Android Developers — R8 docs"}

Review Android R8 / ProGuard configuration for correctness, minimal-keep discipline, and release-build resilience. R8 is the default code shrinker in AGP 8.x — it's ProGuard-compatible (same -keep rule syntax) but with better optimization and bundled obfuscation. Report only genuine problems; don't add -keep rules speculatively.

Review process:

1. Frame what R8 is doing using references/fundamentals.md — shrinking, optimizing, obfuscating, repackaging; what minifyEnabled = true actually triggers.
2. Validate -keep rule discipline using references/keep-rules.md — when to use -keep vs -keepclassmembers vs -keepnames, and why blanket -keep is wrong.
3. For library modules, check consumer-rules.pro using references/consumer-rules.md — what libraries owe their consumers.
4. Check common reflection-library rules using references/library-keep-rules.md — Moshi, Room, Retrofit, Hilt, Glide, kotlinx-serialization.
5. Validate mapping-file workflow using references/mapping-files.md — keeping mapping.txt, deobfuscating stack traces, Crashlytics integration.
6. Diagnose release-build crashes using references/common-crashes.md — ClassNotFoundException, NoSuchMethodException, native-library symbol mismatches.

If doing a partial review, load only the relevant reference files.

Core Instructions

• R8 is default in AGP 3.4+. The proguardFiles directive uses ProGuard rule syntax; R8 interprets them. There's no separate "use R8" flag — minifyEnabled = true turns it on.
• Default to proguard-android-optimize.txt + your proguard-rules.pro. AGP ships sensible defaults via getDefaultProguardFile("proguard-android-optimize.txt").
• Library modules use consumer-rules.pro, not proguardFiles. Rules in consumer-rules.pro are inherited by every consumer that depends on the library. See consumer-rules.md.
• -keep is the heavy hammer — it prevents shrinking, optimization, AND obfuscation for the matched class. Prefer narrower forms (-keepclassmembers, -keepnames) when only one of those is needed.
• Reflection-using libraries (Moshi, Room, Retrofit, Hilt, Glide, kotlinx-serialization) need keep rules. Most ship their own consumer-rules.pro, but some (or custom uses) require app-level additions.
• Always test release builds with minifyEnabled = true before shipping. Many R8 crashes only surface in release.
• Keep the mapping.txt from every release. Without it, post-release crash reports are unreadable obfuscated stack traces.

Output Format

For ProGuard/R8 reviews, organize findings by file. For each:

1. State the file (proguard-rules.pro, consumer-rules.pro, etc.) and line.
2. Name the rule issue.
3. Show before/after.

Skip files with no issues. End with a prioritized summary.

Example output:

proguard-rules.pro

Line 8: -keep class com.kozinga.** { *; } is too broad — defeats shrinking for the entire app code.

# Before
-keep class com.kozinga.** { *; }

# After — keep only what reflection actually touches:
-keep @com.squareup.moshi.JsonClass class * { <fields>; }
-keepclassmembers class com.kozinga.models.** {
    @com.squareup.moshi.Json *;
}

Line 18: -keepnames on a class that's reflectively constructed — should be -keep.

# Before — preserves the name but allows R8 to remove the class:
-keepnames class com.kozinga.WebViewBridge

# After — preserves the class itself:
-keep class com.kozinga.WebViewBridge { *; }

consumer-rules.pro (missing for :core:network)

Library :core:network exposes Retrofit interfaces but doesn't ship consumer-rules.pro — consumers' R8 strips method signatures that Retrofit needs at runtime.

# consumer-rules.pro for :core:network
-keep,allowobfuscation,allowshrinking interface retrofit2.Call
-keep,allowobfuscation,allowshrinking class kotlin.coroutines.Continuation
-keepattributes Signature, InnerClasses, EnclosingMethod

Summary

1. Over-broad keep (high): com.kozinga.** blanket keep defeats shrinking for the entire app.
2. Missing consumer-rules.pro (high): Library :core:network doesn't ship Retrofit-required rules.
3. Wrong keep variant (low): -keepnames where -keep is needed.

End of example.

References

• references/fundamentals.md — what R8 does (shrink / optimize / obfuscate / repackage), how it differs from old ProGuard, full-mode vs compatibility-mode, what minifyEnabled triggers, shrinkResources for resources.
• references/keep-rules.md — -keep, -keepclassmembers, -keepclasseswithmembers, -keepnames, -keepattributes. Class-spec syntax (@Annotation class * { <fields>; }). The hierarchy from most-specific to least-specific.
• references/consumer-rules.md — consumer-rules.pro contract with library consumers. When to use it vs in-tree proguard-rules.pro. Library authors' responsibility for shipping correct rules.
• references/library-keep-rules.md — concrete rules for Moshi (@JsonClass), Room (@Entity/@Dao), Retrofit (annotation-driven methods), Hilt (generated classes), Glide (modules), kotlinx-serialization (annotated classes), reflection-via-Class.forName.
• references/mapping-files.md — mapping.txt retention, deobfuscating release stack traces (retrace), Crashlytics mapping upload, R8 missing-rules report (-printusage, -printseeds, -printmapping).
• references/common-crashes.md — ClassNotFoundException, NoSuchMethodException, InvocationTargetException from missing reflection rules, native-library symbol mismatches (UnsatisfiedLinkError), Kotlin metadata stripping (KotlinClassNotFoundException).