Upgrade Kotlin to 2.4.20-Beta2 - #237
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Move the main build from Kotlin 2.4.10 to 2.4.20-Beta2 and adapt the compiler extension APIs and test goldens for the new compiler. Metro's IR mode no longer invokes App Platform's FIR declaration generators, while downstream Native and Wasm compilations still need FIR package hints to discover contributions. Generate renderer, robot, and scoped binding containers in IR through Metro's contribution API, retain FIR only for cross-module hints, and order App Platform's compiler plugin before Metro's graph transformation. This keeps Metro class generation in IR enabled on every target. Update the affected generated API snapshots and leave the standalone blueprints unchanged.
Move renderer, robot, and scoped target resolution off FIR metadata when Metro's IR class generation is enabled. This keeps JVM consumers on a pure IR path while retaining FIR contribution hints only for cross-module discovery in KLIB targets. Mirror Metro's generation option into the App Platform compiler plugin so the FIR fallback remains mode-correct, and run the box corpus without FIR hints to cover the IR-only behavior.
Metro 1.4.1 generates FIR contribution hints alongside IR class generation on Kotlin 2.4.20+, including Native and Wasm. Restore App Platform's FIR declaration shells and existing IR body fillers, remove the custom option rewriting and all-IR generation path, and make compiler tests exercise Metro's production FIR/IR configuration.
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Kotlin 2.4.20 deprecates `IrAnnotation.symbol`, and fresh CI builds reject the warning under `-Werror`. Read `classSymbol` directly so the compiler plugin remains compatible with the supported IR API.
Metro 1.4.2 was released on 2026-08-14 and fixes typealias resolution in `KClass` annotation arguments, `@Origin`-chain exclusions and replacements, Kotlin/JS provider-field collisions for inherited member injection, Dagger-interop crashes for deeply nested class names, and incremental regeneration when `GraphExtension` members change. These fixes reduce compiler-plugin risk for App Platform’s generated contributions and graph extensions; current call sites require no compatibility changes. Metro also tests Kotlin 2.4.20-RC, which covers the project’s 2.4.20-Beta2 compiler line. Upgrade `dev.zacsweers.metro:compiler`, `dev.zacsweers.metro:gradle-plugin`, and `dev.zacsweers.metro:runtime` from 1.4.1 to 1.4.2 through `gradle/libs.versions.toml`, and update `CHANGELOG.md`. The compiler remains on Java 21, the runtime still declares Kotlin stdlib 2.3.0, and the Gradle plugin keeps kotlinx-serialization JSON 1.11.0, so platform and transitive dependency floors are unchanged. The standalone `blueprints/` projects remain untouched. No publicly discoverable 1.4.2-specific issue was found in Metro’s GitHub tracker, security advisories, or Google Issue Tracker as of 2026-08-14 UTC. Confidence is limited because this is a same-day release. The repository’s Metro version history is monotonic and contains no prior Metro rollback. Release: https://github.com/ZacSweers/metro/releases/tag/1.4.2 Comparison: ZacSweers/metro@1.4.1...1.4.2 GitHub issues: https://github.com/ZacSweers/metro/issues?q=is%3Aissue+%221.4.2%22 Google Issue Tracker: https://issuetracker.google.com/issues?q=%22dev.zacsweers.metro%22%20%221.4.2%22
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Summary
Issues found
Metro 1.4.0 enables IR class generation with Kotlin 2.4.20-Beta2. App Platform's former FIR declaration generators are therefore not invoked, which removes its generated bindings.
Moving the containers to IR uncovered two additional constraints:
The generated contribution containers are implementation details and no longer appear as source-level declarations or in JVM API snapshots.
Validation
apiCheck, Detekt, Android lint, module-structure checks, generated test runners, and ktfmt passed.sampleandrecipespassed.Upstream references: Kotlin 2.4.20-Beta2, Kotlin EAP configuration, Metro compiler API, Metro issue #2576, and Metro PR #2590.