February 2026 monthly summary focusing on K2/JVM ABI generation and source-only ABI improvements across facebook/buck2-prelude and facebook/buck2. Highlights include enhancements to Kotlin module generation, Parcelize integration for CREATOR fields, extensive ABI/stub hygiene, and robust annotation handling. The work improves build stability, reduces runtime classpath surprises, and strengthens Java/Kotlin interop for downstream consumers. Key achievements for the month: - Implemented robust .kotlin_module generation for K2 across files containing only objects/classes and for @file:JvmName annotated files, enabling generation in source-only ABI builds and eliminating the need for source_only_abi_deps. - Enabled and hardened Parcelize integration in K2 ABI generation by running Parcelize IR extensions during ABI generation and constraining extensions to Parcelize to reduce risk, ensuring CREATOR fields are emitted consistently. - Strengthened K2 ABI generation around stubs and dependencies: improved detection and stubbing of missing transitive dependencies, enhanced file facade detection, added support for type aliases, and preserved necessary private/internal types to maintain ABI/metadata consistency. - Fixed critical FIR-to-IR and annotation handling issues: resolved crashes caused by unresolved annotation arguments, consolidated comprehensive @Throws handling across FIR/IR/bytecode paths, and refined removal/retention logic for error-type annotations to maintain correct ABI surface. - Improved metadata and visibility hygiene: strip or preserve private supertypes and declarations where appropriate, and post-process metadata to reflect intended visibility, improving downstream DI/annotation processing compatibility. - Performance and build hygiene improvements: eliminated exponential recursion in error-expression checks, introduced used-classes depfiles for K2 source-only ABI, and tightened plugin gating to avoid unnecessary failures in non-source-only builds. Overall impact: These changes deliver a more reliable, efficient, and interoperable ABI generation workflow for K2 in source-only mode, reduce downstream integration issues for Kotlin/Java interop, and accelerate incremental builds through depfile hygiene and targeted IR extensions. Technologies/skills demonstrated: Kotlin/K2 compiler pipelines (FIR/IR), Kotlin metadata and protobuf handling, IR generation extensions (Parcelize), Java interop, Kotlin bytecode post-processing (ASM, kotlinx-metadata), and build tooling/workflow improvements (depfiles, gating, and test stability).

December 2025 monthly summary focusing on stability, reliability, and business value across Buck2 and Buck2-prelude. Key work centered on code generation robustness, Android SDK integration in ABI builds, and import-resolution improvements, enabling Kosabi rollout and reducing build failures.

2025-11 Buck2 monthly summary: Delivered stability and observability improvements across buck2-prelude and buck2. Key outcomes: (1) Kotlin ABI generation robustness: fixed unresolved constants in annotation parameters and tightened import logic so only SDK types are auto-imported; (2) Structured logging: introduced machine-readable compilation logs via KOTLINCD_INVOCATION and KOTLINCD_ARG to replace brittle regex parsing; (3) Import/stub reliability: ensured non-SDK types on classpath are stubbed appropriately to avoid unresolved references; These changes reduce ABI failures, improve build reliability, and enhance CI telemetry. Technologies demonstrated: Kotlin, Java, Buck2 internals, annotation processing, structured logging.

October 2025 monthly summary focused on stabilizing the K2 ABI generator within the facebook/buck2-prelude repository. Key work centered on ensuring build accuracy and ABI reliability, addressing test failures, and improving artifact packaging.

September 2025: Delivered Kotlin compiler plugin improvements and new Kosabi stub tooling for Buck2 Prelude. Implemented selective abi-gen for K2 targets, fixed SKIP_BODIES propagation in K2JvmAbiFirAnalysisHandlerExtension to ensure IR generation extensions run when bodies are skipped, and opened source stubsgen toolchain for broader tooling support. These changes improve cross-target compatibility, reliability of code generation, and pave the way for Kotlin stub tooling and plugin-based enhancements.

Month 2025-08 summary focusing on delivering Kosabi JVM ABI Gen with K2 support for the Buck2 Prelude repo. Implemented Kotlin K2-based JVM ABI generation with testing attribute, plugin path support, Buck rules integration, and a dedicated compiler plugin. This aligns with open-source ABI-gen 2.0 and strengthens Kotlin tooling in Buck2, laying groundwork for faster ABI generation and improved cross-language interop.

In May 2025, delivered a feature in the Buck2 prelude to default to the Kotlin K2 compiler for Kotlin libraries, aligning library builds with the current toolchain and previous fb_android_library changes. Implemented safeguard logic to set K2 as the default when the language version is unset or below 2.0, and the current Kotlin release is older than 2.0, ensuring consistency across Kotlin library configurations and smoother migrations.

In March 2025, delivered Kotlin-focused enhancements to Buck2 Prelude (facebook/buck2-prelude) with a focus on language version handling and build system modernization. Centralized Kotlin language version control, modernized Kotlin-related build code, and introduced a LanguageVersion helper to validate and manage Kotlin language versions. This enables robust support for language-version flags and K2 compilation within the Buck Kotlin builds and lays groundwork for future Kotlin tooling improvements.

February 2025 – Buck2 Prelude (facebook/buck2-prelude). Focused on delivering Kotlin library build system improvements, centralizing language version handling as a direct parameter, and introducing an option to retain synthetic methods in the Kotlin ABI during API-stubber/ABI generation. These changes standardize Kotlin build configuration, reduce per-target drift, and improve ABI/API-stubber fidelity for Kotlin libraries. No explicit bugs were logged for this repo this month; the work emphasized build stability, reproducibility, and maintainability. Business value includes faster onboarding for Kotlin library builds, easier maintenance, and more robust API surface compatibility across Buck2 prebule. Key achievements for February 2025: - Consolidated Kotlin library build configuration by parameterizing language version (commit: c59bf7f68f8240552c8cb97776606b8fb7f38de6). - Introduced option keep_synthetics_in_class_abi for targets using api-stubber to retain synthetic methods in the Kotlin ABI (commit: ac5df045f263c4b9cd6355f01ebe8893b4aa9c94). - Improved maintainability and consistency of Kotlin build settings across the prelude module, reducing manual per-target adjustments.