Michael Lee

This commit **fixes a bug** in the `apple_library` to `cxx_library` swap rollout by restricting its application exclusively to the **`fb_xplat_cxx_library` context**. Previously, the swap was incorrectly applied to all `fb_apple_library` calls, causing build failures for targets like `xplat/third-party/flatbuffers_1_12`. A new `allow_cxx_library_swap` parameter now controls this behavior, defaulting to `False` for direct `fb_apple_library` usage. Additionally, it resolves a **duplicate modulemap creation issue** by ensuring `cxx_library.bzl` skips modulemap generation when invoked from `apple_library`, which handles its own. This **refinement** prevents unintended build breaks and improves the robustness of the **Apple build system**.

This commit performs **maintenance** on the build system by **removing the `# shim` tag** from the `fb_dirsync_cpp_library` target, specifically its `json` alias. This action declassifies the target from an ongoing shim cleanup effort, acknowledging its legacy status and widespread use with approximately 1,900 consumers. The change ensures this critical, long-standing alias is no longer targeted for removal, effectively preserving its current state within the **build configuration**.

This commit performs **maintenance cleanup** by removing several **dead shim redirect targets** from the `xplat/folly/BUCK` build file. These targets were identified as having no external references beyond `deps_remappings.bzl`, indicating they were completely unused. The removal of these obsolete entries helps streamline the **build configuration** for the `folly` library, reducing unnecessary complexity and improving overall build system hygiene.

This commit **fixes a build issue** related to **`Fbcode` suffix redirection** within the **`folly/rust/iobuf`** module's build configuration. It addresses "weird indirection" in target definitions by modifying the `BUCK` file to correctly handle `iobuf-ffi` targets. Specifically, the change removes `FBCODE` from platform definitions, adds `xplat_preexisting_target_flavors`, and creates an alias for `_iobuf-ffiFbcode`. This **maintenance fix** ensures that the build system properly resolves these targets, preventing build failures and maintaining the integrity of cross-platform builds involving `iobuf-ffi`.

This commit introduces a **new capability** to the **`folly_xplat_library` macro** within `folly/defs.bzl`, enabling **constraint-based redirect selection**. It now leverages `dirsync_redirect` to allow targets to dynamically choose between a local implementation and a redirected one based on platform constraints, facilitating more flexible **cross-platform target management**. This mechanism creates an alias target that intelligently selects the appropriate implementation while preserving **SONAME for ABI compatibility**. Furthermore, targets can opt-out of this redirection for specific scenarios, such as portability shims or to prevent build cycles, providing fine-grained control over the build process.

This commit **refactors** the build system configuration for the `fast-crc32` library within `folly/external`. It **converts existing build targets** in `folly/external/fast-crc32/BUCK` from separate `fbcode_target` and `non_fbcode_target` definitions to a unified `fb_dirsync_cpp_library` macro. This change **simplifies the build process** by merging per-cell `compiler_flags` selects into combined selections and leveraging the `dirsync` macro for automatic fbcode/xplat dispatch. The overall impact is a **more streamlined and maintainable build configuration** for the `fast-crc32` component.

This commit performs a significant **refactoring** and **maintenance** effort within the **Folly build system configuration** by **removing all remaining `synchronization_` shim targets**. Specifically, it deletes deprecated build targets from `folly/init/BUCK` and updates references, such as for `hazptr_thread_pool_executor`, to point directly to their true source. This change eliminates an unnecessary layer of indirection in dependency resolution for **Folly's synchronization components**, also cleaning up `folly/somerge_defs.bzl` by removing references to these now-obsolete shims. The overall impact is a simpler and more direct build graph for **Folly's core libraries**.

This commit **refactors the Folly build system** by **removing a shim target** for `synchronization_atomic_struct` from `folly/BUCK`. It updates dependencies, specifically for `indexed_mem_pool`, to directly reference the canonical `fb_dirsync_cpp_library` target at `xplat/folly/synchronization:atomic_struct`. This cleanup also involves removing entries from `deps_remappings.bzl` and updating regexes in `folly/somerge_defs.bzl` and `arvr so_merge_sequence.bzl` to reflect the direct path. The change streamlines the build configuration for **Folly's synchronization primitives**, eliminating unnecessary indirection and simplifying the dependency graph.

This commit **refactors** the **build system configuration** for `folly`'s `fast-crc32` component by **migrating cross-platform build targets**. Specifically, `non_fbcode_target` definitions for `fast-crc32` are relocated from the monolithic `xplat/folly/BUCK` file to a more specific `xplat/folly/external/fast-crc32/BUCK`. This change improves the **organization and maintainability of build definitions** by co-locating targets closer to their respective source code. Consequently, the `xplat/folly/hash/BUCK` file is updated to reflect these new dependency paths, ensuring continued correct resolution of `fast-crc32` implementations without altering functionality.

This commit **extends the public API** of the **Starlark typing system**, making several crucial traits and types available for external use. Specifically, it re-exports `TyCallArgs`, `TyCustomImpl`, `TyCustomFunctionImpl`, and error types from the `starlark::typing` module, alongside `TypeMatcherAlloc` and `StarlarkValueAsTypeStarlarkValue`. New public accessors like `TyCallArgs::pos()` and `TyCustom::as_any()` are introduced, and `TypingOracleCtx::validate_fn_call()` is made public. This **API extension** is a **new capability** that empowers **downstream crates** to implement **custom parameterized types** and functions, thereby significantly enhancing the extensibility of the Starlark interpreter.

This commit introduces **type-level parameterization for `Select`** within the **Starlark type checker**, allowing `Select[str]` and `Select[int]` to be distinct types. This **new capability** enhances type safety by implementing `TySelect` to represent parameterized `Select` types, updating the `select()` built-in's type inference via `SelectFunctionType`, and correctly propagating type parameters through binary operations like `+`. The changes involve significant updates to the `buck2_interpreter_for_build/src/interpreter/selector.rs` module and a **refactoring** of the core `starlark-rust/starlark/src/typing` module to support general type parameterization, providing a more robust and expressive type system for Starlark users.

This commit introduces a comprehensive suite of **integration tests** for the new **`Select[T]` type parameterization**. These tests validate the type checking behavior across a wide range of scenarios, including basic typed selects, nested types, optional parameters, union types, and semantic validation like branch consistency and compatibility. By providing both passing (`_good.bzl`) and failing (`_bad.bzl`) test cases, this work ensures the **correctness and robustness** of the `Select[T]` feature and its type checking rules. This significantly improves the **quality assurance** for this new type system capability, covering expected successes and error conditions.

This commit **adjusts the build configuration** for the **`folly:dynamic` library** by restricting its supported Apple SDKs. Specifically, the `folly/BUCK` file is updated to use `DEFAULT_APPLE_SDKS` instead of `ALL_APPLE_SDKS` for the `folly:dynamic` target. This **maintenance change** addresses an underlying dependency incompatibility that prevented `folly:dynamic` from building correctly with all Apple SDKs. The modification is a **fix for existing build issues** and is not expected to introduce new breakage, as the broader SDK support was already non-functional.

This commit provides a **bug fix** for the **`somerge` merge map generation** process, specifically addressing issues caused by `dirsync redirect` renaming targets with a `_` prefix. It updates `compute_merge_maps.py` to generate more robust regexes that optionally match `_`-prefixed targets within `dirsync redirect` paths like `xplat/folly`, and also makes the `fbsource` cell prefix optional in all generated regexes. Additionally, it **normalizes `_`-prefixed targets** from `buck cquery` results and filters out invalid entries, preventing merge cycles and duplicate entries. This **maintenance** work ensures the correct functioning of `somerge` for projects like **Folly** and **QUIC**, whose `somerge_defs.bzl` files were regenerated.

This commit **improves documentation** by adding comprehensive doc comments to methods within several key **typing traits** in the Starlark Rust implementation. Specifically, it documents the `TyCustomImpl`, `TyCustomFunctionImpl`, and `TypeMatcherAlloc` traits, located in `starlark-rust/starlark/src/typing/custom.rs`, `starlark-rust/starlark/src/typing/function.rs`, and `starlark-rust/starlark/src/values/typing/type_compiled/alloc.rs` respectively. This **maintenance** effort enhances code clarity and developer understanding of how custom types and functions are handled within the **Starlark type system**. The added comments will aid future development and debugging by providing clearer explanations of these critical interfaces.

This commit introduces a **new capability** to the **Starlark type system**, enabling **parameterized type expressions** (e.g., `Select[T]`) for custom types beyond just `list` and `dict`. It achieves this by adding the `TyCustomImpl::parametrize` trait for custom type implementations and integrating this logic into `StarlarkValueAsTypeStarlarkValue::at()` for validation and application. The **Starlark compiler and linting passes** are updated to correctly handle `[]` indexing on types with `eval_type()`. This **API extension** makes several core typing traits and types public, such as `TyCustomImpl` and `TyCallArgs`. Consequently, **downstream crates can now define and implement their own custom parameterized types**, significantly enhancing the expressiveness of the Starlark type system.

This commit **removes an unnecessary build shim target** named `folly:experimental_symbolizer_symbolizer` from the `folly/BUCK` file. It **refactors** the **build system** by updating dependency references to directly point to the actual symbolizer component, rather than through the now-deleted shim. This **cleanup** simplifies the build configuration for the `folly` library's symbolization capabilities, ensuring a more direct and efficient dependency graph. This **maintenance** task streamlines the project's build definitions by eliminating obsolete build configurations.

This commit introduces **new tests** to the **Starlark type system**, specifically verifying the behavior of the `TyBasic::parametrize()` path. It ensures that type parameterization for **`list` and `set` types** correctly resolves annotations like `list[str]` and `set[int]`. Furthermore, these tests confirm that attempting to parametrize with too many type arguments, such as `list[str, int]`, results in a clear and expected error. This **testing** work enhances the **robustness and correctness** of type resolution within the `starlark-rust` project.

This commit performs **maintenance** by **removing obsolete build targets** from the project configuration. These targets were identified as no longer existing or being used, indicating a cleanup of the build system. The change helps to streamline the build process and reduce unnecessary complexity by eliminating dead code references. This is a **cleanup** operation affecting the **build configuration**.

This commit performs a significant **build system cleanup** by **removing 16 redundant `non_fbcode_target` shims** from the `xplat/folly/BUCK` and `xplat/folly/experimental/coro/BUCK` build files. These shims previously served as indirect redirects to canonical target locations, and their removal simplifies the overall build configuration. As part of this **refactoring and maintenance** effort, the `xplat/ems/utils/EMSSchemaStore` module is updated to directly depend on `xplat/folly/io:fs_util`, eliminating its reliance on a now-removed shim. This change improves the clarity and efficiency of the **build dependency graph** across these core libraries.