Restore R8 per-function DCE: sync getValueCached + ProGuard rule fix

[kirich1409]

What changed

Restores R8 per-function dead-code elimination for the codegen-emitted is*Enabled() extensions, which was silently degraded by PR #200 (multi-module sample). Two coupled latent bugs are addressed:

1. ConfigValues got a sync read path (getValueCached) so the codegen-emitted is*Enabled() extensions can be non-suspend again. The internal snapshot is a copy-on-write AtomicReference<Map<String, ConfigValue<*>>>, populated via write-through from override / fetch / suspend getValue. Cold reads return ConfigValue(defaultValue, Source.DEFAULT) — forgiving like Firebase Remote Config.
2. ProguardRulesGenerator was targeting the legacy @file:JvmName-derived class name (Featured_FlagExtensionsKt), but PR D removed @file:JvmName so the real Kotlin-compiled class is GeneratedFlagExtensions…Kt. The -assumevalues rules silently no-op'd; R8 couldn't apply per-function DCE in real consumer builds. Rule target now derives from ExtensionFunctionGenerator.fileName(modulePath) — single source of truth for the class name.

ExtensionFunctionGenerator stops emitting suspend and switches the underlying call to getValueCached. The JVM signature returns to plain boolean isXEnabled(ConfigValues) (no Continuation), matching what ProguardRulesGenerator emits. SyntheticBytecodeFactory + R8 elimination tests sync to the new class name so the shrinker-tests suite actually exercises the production rule shape.

ConfigValues.isEnabled extension is no longer suspend — delegates to getValueCached. Breaking change; callers can drop runBlocking { … } / coroutine-scope wrappers. Featured does not keep API compatibility.

resetOverride(param) re-resolves through the provider priority chain synchronously (Phase A review caught a race in the initial background-launch implementation). ConfigValues no longer needs an internal coroutine scope or AutoCloseable lifecycle.

Why

PR #200 (multi-module sample) introduced suspend on the generated extensions because the underlying ConfigValues.getValue was suspend. This was tactical — accepted by the maintainer with the understanding that R8 DCE would be silently degraded until a proper sync path landed. This PR closes that gap.

Scope rationale (Phase 2 was dropped)

Initial design proposed a SnapshotConfigValueProvider bulk warm-up so prod providers (DataStore / NSUserDefaults / Firebase) could pre-fill the snapshot at app start. After discussion, the production direction is per-module ConfigValues — each feature module owns a small ConfigValues instance with only its own params, warmed via observe/getValue naturally. Bulk aggregation matters only for the debug UI, which already iterates GeneratedFeaturedRegistry.all lazily. Per-module ConfigValues architecture itself is filed as a separate follow-up (tracker task #16) — out of scope here.

Artifacts

• swarm-report/proguard-suspend-followup-plan.md — architecture-expert design proposal (accepted with Q4 picked as Option B = re-resolve through priority chain).
• swarm-report/sync-getvaluecached-state.md — phase tracker with user-confirmed decisions baked in.
• Per-phase stage reports sync-getvaluecached-stage-1.md, stage-3.md, stage-4-fix.md, stage-5.md.

How to test

CI matrix runs the full Gradle suite. Verified locally:

• ./gradlew :core:test :core:koverVerify — green, ≥ 90% line coverage
• ./gradlew -p build-logic :featured-gradle-plugin:check — green
• ./gradlew :featured-shrinker-tests:test — green (R8 elimination tests now actually exercise the real class name)
• ./gradlew :sample:android-app:assembleDebug — green
• ./gradlew :sample:desktop:assemble — green
• ./gradlew :sample:shared:linkDebugFrameworkIosSimulatorArm64 — green
• ./gradlew spotlessCheck — green

Manual QA: the sample's runtime path uses observe-bridges (Flow<T> + stateIn), so the existing PR #200 24/24 Pixel 10 + Desktop + iOS Sim runs cover this PR's runtime behavior — no UI surfaces changed.

Release Notes

Added

• ConfigValues.getValueCached(param) — non-suspend cached reader; returns ConfigValue<T> with Source.DEFAULT before any warm-up write. Safe from any thread including Android main.

Changed

• Breaking: ConfigValues.isEnabled(param) extension is no longer suspend. Drop runBlocking { … } / coroutine-scope wrappers; the call site can stay in a @Composable or any sync context.
• Breaking: codegen-emitted is<Name>Enabled() / get<Name>() extensions are no longer suspend. Same migration as above.
• ConfigValues.override / fetch / suspend getValue write through to the in-memory snapshot so subsequent getValueCached reads see the value with the source the provider reported.
• ConfigValues.resetOverride re-resolves through the provider priority chain inline before returning.

Fixed

• R8 per-function DCE for unused flag accessors: -assumevalues rules now target the real Kotlin-compiled class name (GeneratedFlagExtensions…Kt). Previously the rules silently no-op'd after PR Multi-module sample showcasing Featured aggregator plugin #200 removed @file:JvmName. Module paths with hyphens (:feature-checkout) also produced JVM-illegal class names — corrected via the shared ExtensionFunctionGenerator.fileName derivation.

Status

Phase	Outcome
Phase 1 (:core sync API)	done, 651126b
Phase 2 (bulk SnapshotConfigValueProvider)	dropped (per-module is the production pattern)
Phase 3 (codegen non-suspend)	done, 6c1208a
Phase 4 (ProGuard class-name fix)	done, 2a16bc7
Phase 5 (docs / CHANGELOG / sample)	done, 39d7e0c
/finalize Phase A (code-reviewer opus)	WARN → fixed 1bf0cbc
/check (build / lint / tests / shrinker)	PASS

Follow-ups (not blocking)

• Per-module ConfigValues architecture (task feat(gradle-plugin): generate ProGuard/R8 -assumevalues rules for Android/JVM #16) — feature modules will own their own ConfigValues; debug UI remains the only aggregator.

🤖 Generated with Claude Code

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[Copilot]

Pull request overview

This PR restores R8 per-function dead-code elimination for codegen-emitted flag accessors by reintroducing a synchronous cached read path in ConfigValues and fixing the ProGuard rule generator to target the actual Kotlin-compiled extensions class name.

Changes:

• Add ConfigValues.getValueCached() backed by an in-memory AtomicReference snapshot, and switch ConfigValues.isEnabled() to a non-suspend cached read.
• Update ExtensionFunctionGenerator to emit non-suspend is*Enabled() / get*() extensions that delegate to getValueCached().
• Fix ProguardRulesGenerator (and shrinker tests) to derive the correct GeneratedFlagExtensions…Kt JVM class name via ExtensionFunctionGenerator.fileName().

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
sample/CLAUDE.md	Updates sample guidance to use getValueCached for sync reads and reflect non-suspend generated accessors.
featured-shrinker-tests/src/test/kotlin/dev/androidbroadcast/featured/shrinker/r8/R8IntFlagEliminationTest.kt	Updates shrinker test documentation to match the new generated extensions class naming.
featured-shrinker-tests/src/test/kotlin/dev/androidbroadcast/featured/shrinker/r8/R8BooleanFlagEliminationTest.kt	Updates shrinker test documentation to match the new generated extensions class naming.
featured-shrinker-tests/src/test/kotlin/dev/androidbroadcast/featured/shrinker/bytecode/SyntheticBytecodeFactory.kt	Aligns synthetic bytecode internal class names with GeneratedFlagExtensions…Kt output.
core/src/commonTest/kotlin/dev/androidbroadcast/featured/ConfigValuesExtensionsTest.kt	Adjusts tests for isEnabled becoming non-suspend and snapshot-driven.
core/src/commonTest/kotlin/dev/androidbroadcast/featured/ConfigValuesCachedTest.kt	Adds unit tests for getValueCached behavior and snapshot write-through semantics.
core/src/commonMain/kotlin/dev/androidbroadcast/featured/ConfigValuesExtensions.kt	Changes isEnabled extension to be synchronous and snapshot-based with updated KDoc.
core/src/commonMain/kotlin/dev/androidbroadcast/featured/ConfigValues.kt	Implements the snapshot + getValueCached, and wires write-through from getValue/override/resetOverride.
CHANGELOG.md	Documents the new sync API and the restored R8 DCE behavior.
build-logic/featured-gradle-plugin/src/test/kotlin/dev/androidbroadcast/featured/gradle/ProguardRulesGeneratorTest.kt	Updates ProGuard generator tests to expect the new Kotlin file-derived JVM class name.
build-logic/featured-gradle-plugin/src/test/kotlin/dev/androidbroadcast/featured/gradle/FeaturedPluginIntegrationTest.kt	Updates integration test expectations for the new extensions class name.
build-logic/featured-gradle-plugin/src/test/kotlin/dev/androidbroadcast/featured/gradle/ExtensionFunctionGeneratorTest.kt	Updates generator tests for non-suspend extensions and getValueCached usage.
build-logic/featured-gradle-plugin/src/main/kotlin/dev/androidbroadcast/featured/gradle/ProguardRulesGenerator.kt	Fixes -assumevalues rule target class name derivation using fileName() as source of truth.
build-logic/featured-gradle-plugin/src/main/kotlin/dev/androidbroadcast/featured/gradle/ExtensionFunctionGenerator.kt	Emits non-suspend extension functions and removes the legacy jvmFileName path.

Comments suppressed due to low confidence (1)

core/src/commonMain/kotlin/dev/androidbroadcast/featured/ConfigValues.kt:235

• clearOverrides() clears the local provider but intentionally leaves the snapshot unchanged. With the new sync read path (getValueCached / isEnabled), this means previously overridden params may continue to read as Source.LOCAL even after clearing. Consider updating the snapshot here (e.g., dropping entries whose cached source == LOCAL) so cached reads reflect that overrides were cleared.

    /**
     * Removes all locally overridden values, resetting the local provider to an empty state.
     *
     * After this call, every [getValue] call falls back to the remote provider or
     * [ConfigParam.defaultValue]. Has no effect when no local provider is configured.
     *
     * Note: the sync snapshot is **not** cleared here. Individual param slots are updated
     * lazily when [getValue] or [resetOverride] is called for each param. This is consistent
     * with the fact that [ConfigValues] does not maintain a registry of all known params.
     */
    public suspend fun clearOverrides() {
        localProvider?.clear()
    }