Cameron Pickett

This commit **improves the developer experience** for Rust compilation on `aarch64` platforms by **suppressing persistent warnings** related to unstable target features such as `v8.1a` and `crypto`. It introduces a **new custom Rust target definition** (`aarch64-unknown-linux-gnu-unstable.json`) within the **Rust build system**, which explicitly declares these features to bypass the compiler's warning mechanism. This **maintenance change** effectively cleans up noisy build logs for developers using ARM64 as their primary environment. Additionally, it includes **documentation** (`README.md`) explaining the purpose and generation of custom targets.

This commit **adds a new capability** to the **Rust toolchain** by introducing a `restricted_rustc_flags` attribute in `prelude/rust/rust_toolchain.bzl`. This **enhancement** allows toolchain definitions to specify `rustc_flags` (e.g., `-Ctarget-feature`) that are disallowed in individual `rust_library`, `rust_binary`, and `rust_unittest` targets. A new **analysis-time validation** (`_check_restricted_rustc_flags` in `prelude/rust/build.bzl`) will now `fail()` builds if restricted flags are detected, ensuring **policy enforcement** across Rust targets. Targets that genuinely require a restricted flag can explicitly opt out using the new `uses_restricted_rustc_flags` attribute, which is added to common Rust rule definitions in `prelude/decls/rust_rules.bzl`. This **improves build integrity and security** by preventing unintended or malicious flag usage.

This commit **fixes an incidental breakage in the Windows Rust build** by adjusting how Rust-related providers are handled. It modifies the `_remove_rust_providers_impl` function in `prelude/rust/linkable_symbol.bzl` to explicitly filter `RustSources` providers, which was causing build failures. Additionally, `prelude/native.bzl` is updated to expose `RustSources` through an internal mechanism, enabling this fix. This **bug fix** ensures the **Rust build system** functions correctly on **Windows platforms** by preventing incorrect provider removal.

This commit introduces a **new capability** to the **Rust toolchain configuration** by adding an optional `sanitizer` attribute to the `RustToolchainInfo` provider. Defined in `prelude/rust/rust_toolchain.bzl`, this attribute allows specifying a Rust sanitizer, defaulting to `None` to maintain existing behavior. The build logic in `prelude/rust/build.bzl` is updated to incorporate the corresponding `-Zsanitizer=<value>` flag into `rustc` arguments via `_compute_common_args` when a sanitizer is configured through the toolchain. This enhancement provides the foundation for future per-platform configuration of Rust sanitizers, enabling more granular control over build flags through `select()`.

This commit introduces a **bug fix** to resolve **non-deterministic Rust crate hashes (SVH)** that occurred between local and remote builds due to recent `rustc` changes in source remapping. It enhances the **Rust compilation infrastructure** by **materializing transitive Rust sources** for remote actions, ensuring consistent source availability across environments. Modifications to `prelude/rust/build.bzl`, `prelude/rust/context.bzl`, `prelude/rust/rust_library.bzl`, and `prelude/rust/sources.bzl` now correctly collect and pass all necessary dependency sources. This ensures `rustc` consistently handles literal desugaring, thereby guaranteeing **deterministic Buck builds** for Rust projects and preventing compilation inconsistencies.

This commit performs a **refactoring** of the **Rust build prelude** by extracting the `CrateName` record and the `crate_name_as_cmd_arg` function into a new, dedicated file, `prelude/rust/crate_name.bzl`. This change specifically **breaks a potential load cycle** within the build system's dependency graph, which would otherwise be introduced by an upcoming change. Files such as `prelude/rust/context.bzl`, `prelude/rust/extern.bzl`, `prelude/rust/build.bzl`, `prelude/rust/link_info.bzl`, and `prelude/rust/rust-analyzer/provider.bzl` have been updated to reflect the new import paths. This **maintenance** effort improves the modularity and robustness of the **Rust build system**, ensuring its stability for future developments without altering external behavior.

This commit performs a **refactoring** within the **Rust build prelude** by **extracting the `DepCollectionContext` definition** from `prelude/rust/context.bzl` into a new, dedicated file, `prelude/rust/dep_context.bzl`. This strategic move is a **preparatory step** designed to **break a potential load cycle** in the build system's dependency graph, which would otherwise arise from future changes. Consequently, all modules that utilize this context, including `build.bzl`, `cargo_buildscript.bzl`, and `rust_library.bzl`, have been updated to import `DepCollectionContext` from its new location. This ensures the stability and correctness of the dependency resolution for Rust targets.

This commit **reverts** a prior change (D96685477) that aimed to address **OSS CI test failures** related to null `remap_paths_to` arguments. The original change was a **refactoring** within the **Rust build prelude** (`prelude/rust/build.bzl`), specifically altering the construction of the `--remap-paths-to` argument in `generate_rustdoc_test` and `_rustc_invoke` to utilize `cmd_args` directly. This revert undoes that refactoring, effectively restoring the previous logic and potentially reintroducing the CI test issues that the original commit sought to resolve.

This commit **reverts** a previous change that added `remap_paths_to` arguments to the `rustdoc` and `rustc` command invocations within the **Rust build rules**. It specifically undoes modifications to the `generate_rustdoc_test`, `rust_compile`, and `_rustc_invoke` functions in `prelude/rust/build.bzl`. This **revert** removes the logic for handling `/buck_remapped/` prefixes and diagnostic stripping, likely addressing an issue introduced by the original "fix" related to Rust build diagnostics or path handling.

This commit **fixes a bug** in the **Rust build rules** within `prelude/rust/build.bzl` that caused **OSS CI tests** to fail when `remap_paths_to` was not explicitly set. It modifies the `generate_rustdoc_test` and `_rustc_invoke` functions to conditionally include the `--remap-paths-to` argument for `rustdoc` and `rustc` invocations. This ensures the argument is only passed when `toolchain_info.remap_paths_to` is present, preventing errors from null or unset values. This **bug fix** improves the robustness of the **Rust build system** for projects in open-source environments by correctly handling toolchain configurations.

This commit **fixes non-deterministic Source Version Hashes (SVH)** in Rust builds on remote execution workers, stemming from Rust 1.94.0's altered source map lookup logic. It resolves this by modifying the **Rust build system** to prepend a non-existent `/buck_remapped/` prefix to `--remap-path-prefix` arguments, ensuring `rustc` consistently fails to find remapped source files. The **Rust toolchain configuration** (`prelude/rust/rust_toolchain.bzl`) is updated to support this new remapping strategy. Crucially, the `rustc` action script (`prelude/rust/tools/rustc_action.py`) is enhanced to **strip this prefix from all diagnostic output**, maintaining clean paths for users. This **bug fix** ensures **consistent Rust crate SVH** across local and remote builds, preventing unexpected desugaring differences and improving overall build reliability.

This commit introduces a new boolean attribute, `use_content_based_paths`, to the **common Rust build rule attributes** defined in `prelude/decls/rust_rules.bzl`. This is a **preparatory change** that adds the necessary wiring to the **Rust build system** for a future feature. It enables an **incremental roll-out and roll-back mechanism** for "content-based paths" within the Rust prelude, allowing for controlled adoption of this new behavior in subsequent changes. The attribute is currently inactive by default and does not alter existing build logic, serving purely as infrastructure for future development.

This commit **fixes** an issue where `compiler-builtins` was not correctly detecting `f16_enabled` and `f128_enabled` configurations during **sysroot compilation**. It introduces an `enable_nightly_cfgs` attribute to the `get_rustc_cfg` rule in `prelude/rust/tools/tool_rules.bzl`, which now explicitly sets `RUSTC_BOOTSTRAP=1` in the environment when querying `rustc --print=cfg`. This **maintenance** change ensures that the **Rust toolchain's fundamental `compiler-builtins` library** correctly identifies and enables support for half-precision and quad-precision floating-point types, preventing potential compilation failures or incorrect feature availability.

This commit introduces a **new capability** by plumbing `libclang` through the **C++ toolchain infrastructure**. It adds a `libclang` attribute to the `cxx_toolchain` definition in `cxx_toolchain.bzl` and defines a corresponding field within the `CxxToolchainInfo` provider in `cxx_toolchain_types.bzl`. This **infrastructure enhancement** allows `libclang` to be specified and accessed via the C++ toolchain override mechanism. The change is foundational, enabling subsequent **`bindgen` builds** to reference and utilize `libclang` effectively.

This commit **removes the logic for inferring and passing xplat platforms** within the **`integrations/rust-project/src/buck.rs`** module, specifically impacting how **Buck commands are constructed and executed**. This **fix** and **simplification** addresses issues where the previous "guessing" mechanism for cross-platform configurations was causing problems, as detailed in internal discussions. By eliminating this unnecessary complexity, the change aims to improve the reliability of **cross-platform support** for Rust projects and streamline **Buck command invocation**.

This commit introduces a **new feature** to the **`rust_library`** rule by adding support for a `[stripped]` nested subtarget within its default providers. This enhancement simplifies the process of obtaining stripped artifacts, such as `cdylib`s, directly from the build system. By exposing this subtarget, developers can more easily manage the size and distribution of their Rust-generated binaries. The change primarily affects the `_default_providers` logic within `prelude/rust/rust_library.bzl`, providing a more streamlined way to access stripped outputs.

This commit introduces a **new capability** to correctly parse and expand "atfiles" within `rustc_flags` during **rust-project generation**, ensuring `rust-analyzer` receives all necessary compiler flags. It adds an `expand_atfile` function and integrates this logic into the `cfgs` module in `integrations/rust-project/src/target.rs`. Concurrently, the **`RustAnalyzerInfo` provider** in `prelude/rust/rust-analyzer/provider.bzl` is **refactored** to directly expose `edition`, `features`, and `rustc_flags`. These fields are then consumed by `_process_target_config` in `prelude/rust/rust-analyzer/resolve_deps.bxl`, streamlining flag propagation. This change significantly improves the **IDE experience** for projects where build scripts dynamically generate `rustc_flags`.

This commit **fixes build failures** for the **`folly/rust/iobuf`** module on certain Apple platforms, specifically WatchOS. It **updates the `BUCK` file** (`folly/rust/iobuf/BUCK`) to explicitly scope down the `iobuf` forwarding aliases, ensuring they only target **iOS and macOS SDKs**. This **build configuration fix** prevents unsupported underlying targets from being included in builds for platforms like WatchOS, thereby resolving existing failures and improving the overall reliability of the build system for Apple targets.

This commit **refactors** the **Rust library build rules** within `prelude/rust/rust_library.bzl` to enhance control over output styles. It introduces logic to filter the generated library artifacts, ensuring that **shared libraries** are only produced when the `preferred_linkage` configuration explicitly allows for them. This **maintenance fix** addresses previous feedback by preventing the unnecessary creation of shared libraries, thereby improving the correctness and efficiency of the **Rust build process** by aligning output with specified linkage preferences.

This commit performs a **maintenance refactoring** by **updating the build configuration** for the **`app/buck2_resource_control`** module. It specifically **removes usage of deprecated Rust build macros**, changing the `rust_library` macro load path from `fbcode_macros` to the current `fbsource` definition within its `BUCK` file. This ensures the module adheres to the latest **Buck2 build system** standards and avoids reliance on obsolete macro definitions. The change is part of a broader effort to eliminate all usages of the old `fbcode_macros//build_defs:rust_(library|binary|unittest).bzl` paths.