Extract R8 DCE verification into featured-shrinker-tests module

.gitignore

@@ -1,3 +1,4 @@
+swarm-report/
 *.iml
 .kotlin
 .gradle

docs/guides/r8-verification.md

@@ -0,0 +1,78 @@
+# R8 Dead-Code Elimination Verification
+
+## Why it matters
+
+Featured's core guarantee for local flags is that when a flag value is fixed at build time,
+the code reachable only through the disabled branch is completely removed from the final APK.
+This relies on R8 honouring the `-assumevalues` ProGuard rules generated by
+`ProguardRulesGenerator`.
+
+A rule that is syntactically correct but semantically wrong would silently fail to eliminate
+dead code. The `featured-shrinker-tests` module gives automated, deterministic verification
+that the exact rule format produced by the plugin is sufficient for R8 to perform DCE.
+
+## How it works
+
+The tests use a three-step synthetic pipeline:
+
+1. **Bytecode generation (ASM)** — `SyntheticBytecodeFactory` builds `.class` files in
+   memory that mirror the structure the plugin generates at build time: a `ConfigValues`
+   holder, an extensions class that reads from it, branch-target classes (`IfBranchCode`,
+   `ElseBranchCode`, `PositiveCountCode`), and a caller entry point.
+
+2. **Rules generation** — `ProguardRulesWriter` writes `.pro` files in the exact format
+   `ProguardRulesGenerator` produces, optionally including the `-assumevalues` block.
+
+3. **R8 invocation** — `R8TestHarness.runR8()` calls R8 programmatically via
+   `R8Command.builder()`, producing an output JAR with DCE applied.
+
+After each run, `JarAssertions` inspects the output JAR and asserts which classes are
+present or absent, proving that the rule caused (or did not cause) elimination.
+
+## Test scenarios
+
+### Boolean flags (`R8BooleanFlagEliminationTest`)
+
+| Test | Rule | Expected |
+|------|------|----------|
+| `if-branch class is eliminated when boolean flag returns false` | `-assumevalues … return false` | `IfBranchCode` absent; `ElseBranchCode` present |
+| `else-branch class is eliminated when boolean flag returns true` | `-assumevalues … return true` | `ElseBranchCode` absent; `IfBranchCode` present |
+| `both branch classes survive when no boolean assumevalues rule is present` | No `-assumevalues` | Both classes present |
+
+The third test is a control: it proves that elimination is caused by the rule, not by R8's
+own constant-folding.
+
+### Int flags (`R8IntFlagEliminationTest`)
+
+| Test | Rule | Expected |
+|------|------|----------|
+| `guarded class is eliminated when int flag is assumed to return zero` | `-assumevalues … return 0` | `PositiveCountCode` absent; `IntCaller` present |
+| `guarded class survives when int flag has no assumevalues rule` | No `-assumevalues` | Both classes present |
+
+With `-assumevalues return 0`, R8 constant-folds `0 > 0` to `false` and eliminates the
+guarded block entirely.
+
+## Running the tests
+
+```bash
+./gradlew :featured-shrinker-tests:test
+```
+
+To run only one test class:
+
+```bash
+./gradlew :featured-shrinker-tests:test --tests "dev.androidbroadcast.featured.shrinker.r8.R8BooleanFlagEliminationTest"
+```
+
+## Adding new scenarios
+
+1. **New flag type** — add bytecode generators in `SyntheticBytecodeFactory.kt`, JAR
+   assembler functions in `JarAssembler.kt`, rule writers in `ProguardRulesWriter.kt`, and
+   a new test class in `r8/` that extends `R8TestHarness`.
+
+2. **New rule variant** — add a `write*Rules()` function in `ProguardRulesWriter.kt` and a
+   corresponding `@Test` method in the relevant test class.
+
+3. **Verifying a rule format change** — update the `write*Rules()` function to match the
+   new format produced by `ProguardRulesGenerator`, then run the tests to confirm DCE still
+   works.

featured-gradle-plugin/build.gradle.kts

@@ -57,6 +57,4 @@ mavenPublishing {
 dependencies {
     testImplementation(gradleTestKit())
     testImplementation(libs.kotlin.testJunit)
-    testImplementation(libs.r8)
-    testImplementation(libs.asm)
 }