Configuring R8 For Compose

# Configuring R8 for Compose — Trust Consumer Rules, Avoid Blanket Keeps

R8 is the only supported shrinker — ProGuard is deprecated. Compose ships consumer ProGuard rules, so most apps need **no** Compose-specific keep rules. The big modern wins come from R8 full mode (default since AGP 8.0): lambda grouping, `sourceInformation()` stripping, constant-folding of composable args, and `ComposerImpl` devirtualization. This skill teaches Claude to set R8 up minimally and refuse over-broad keeps that defeat those wins.

## When to use this skill

- Setting up a new Compose app's release variant for the first time.
- A PR adds `-keep class androidx.compose.** { *; }` or any other Compose-wide keep — push back and apply this skill.
- A release build crashes after enabling minification — the cause is almost always a missing keep on a reflective consumer, not on Compose itself.
- APK size review surfaces a large `classes.dex` and the developer wants to know why.
- The first time `isMinifyEnabled = true` is being flipped on, before any release benchmark is run.
- Cross-link from `../../measurement/testing-compose-in-release-mode/SKILL.md` whenever release measurement is being set up.

## When NOT to use this skill

- The app is not yet ready to ship a release variant — wait until perf and crash budgets are in scope.
- The developer is debugging a code-level bug (logic error, race, wrong state). R8 issues manifest as `ClassNotFoundException`, `NoSuchMethodError`, or empty reflection results — not behavioral bugs.
- The release variant has been measured and is fine — do not pre-emptively add keep rules.
- The perf concern is recomposition, layout phase, or stability — see the relevant `stability/` or `recomposition/` skills.

## Prerequisites

- AGP 8.0+ for R8 full mode default. If on older AGP, full mode must be explicitly enabled in `gradle.properties` with `android.enableR8.fullMode=true`.
- A buildable release variant (debug-signed is fine while iterating — see `../../measurement/testing-compose-in-release-mode/SKILL.md` for measurement signing).
- Kotlin 2.0+ with the `org.jetbrains.kotlin.plugin.compose` plugin so Compose's bundled consumer rules are wired correctly through dependency resolution.
- Familiarity with the difference between `proguard-android.txt` (no R8 optimizations) and `proguard-android-optimize.txt` (R8 optimizations on).

## What R8 actually does for Compose (since AGP 8.0)

Surface these to the developer when they ask "why bother" or push back against minification:

1. **Lambda grouping.** R8 merges many of Compose's generated lambda classes, reducing dex size and method count.
2. **`sourceInformation()` stripping.** Each composable emits a string of source-position metadata. R8 removes it from release builds — smaller APK and less work per recomposition.
3. **Composable arg constant-folding.** Constants that would have been wrapped by Live Literals in debug are now folded back into `if (changed and 1 == 0)` style checks the recomposer can short-circuit.
4. **`ComposerImpl` devirtualization.** R8 devirtualizes hot calls into Compose's runtime, which is a major contributor to the cited frame-render improvement.
5. **Resource shrinking.** Paired with `isShrinkResources = true`, R8 strips unreachable drawables, strings, and layout XML.

Cited measurement: roughly **75 percent startup gain** and **60 percent frame-render gain** debug to release. Source: Ben Trengrove, "Why should you always test Compose performance in release" (Android Developers Medium).

## Workflow

- [ ] **1. Configure the release buildType.** This is the entire happy-path config — no Compose-specific keeps needed:

```kotlin
// app/build.gradle.kts
android {
    buildTypes {
        release {
            isMinifyEnabled = true
            isShrinkResources = true