`rust_proc_macro`

Rust procedural macro compiled with rustc.

Description#

Compiles a Rust procedural macro for the execution host. Downstream Rust targets consume the output through --extern as a procedural-macro dependency instead of a normal target dependency.

Attributes#

Attribute	Type	Required	Default	Description
`crate_name`	string	no	target name	Rust crate name passed to `rustc`; `-` and `.` are rewritten as `_` when omitted
`crate_root`	string	no	`src/lib.rs`	Package-relative macro root
`edition`	string	no	`2021`	Rust edition passed to `rustc`
`features`	list<string>	no	`[]`	Cargo feature names lowered to `--cfg=feature=...` flags
`crate_features`	list<string>	no	`[]`	Bazel-compatible alias for `features`
`target`	string	no	host target	Rust target triple passed to `rustc --target`
`env`	map<string, string>	no	`{}`	Environment variables for rustc, matching Buck2's `env` attribute
`rustc_env`	map<string, string>	no	`{}`	Bazel-compatible rustc environment variables
`rustc_env_files`	list<string>	no	`[]`	Files with `NAME=value` entries merged into the rustc environment before `env` and `rustc_env`
`rustc_flags`	list<string>	no	`[]`	Additional `rustc` flags appended after Once-managed flags
`cap_lints`	string	no	empty	Optional rustc lint cap passed as `--cap-lints`; generated Cargo dependencies use `allow`
`linker`	string	no	empty	Optional linker path passed as `-C linker=...`; defaults to `cc` for host Unix binary-like targets and to the Android NDK clang wrapper for Android targets when available
`linker_flags`	list<string>	no	`[]`	Additional linker flags lowered to `-C link-arg=...`
`native_linkopts`	list<string>	no	`[]`	Shared Rust compatibility attribute for native-producing Rust target kinds
`exported_linker_flags`	list<string>	no	`[]`	Buck-compatible alias for native linker flags propagated to downstream native consumers
`exported_post_linker_flags`	list<string>	no	`[]`	Buck-compatible propagated linker flags appended after normal exported linker flags
`linker_script`	string	no	empty	Package-relative linker script passed to the linker and included in the compile action inputs
`android_abi`	string	no	inferred	Android ABI directory for dynamic library outputs, such as `arm64-v8a`
`android_api`	int	no	`23`	Android API level used to select the NDK clang wrapper for Android targets
`android_ndk`	string	no	`ANDROID_NDK_HOME`	Android NDK root used to find clang wrapper linkers
`data`	list<string>	no	`[]`	Runtime data file globs propagated to downstream Rust binaries and tests
`compile_data`	list<string>	no	`[]`	Bazel-compatible compile-time data file globs included in the rustc action inputs
`crate_aliases`	map<string, string>	no	`{}`	Map dependency label, package name, or crate name to the local extern crate name
`aliases`	map<string, string>	no	`{}`	Bazel-compatible alias map from dependency label or crate name to local extern crate name
`named_deps`	map<string, string>	no	`{}`	Buck-compatible alias map from local extern crate name to dependency label or crate name
`cargo_package`	string	no	empty	Cargo package name used to select direct external deps from a `cargo_dependencies` dependency set. Defaults to `CARGO_PKG_NAME` when present
`build_script`	string	no	empty	Package-relative Cargo build script path run before `rustc`; common `cargo:rustc-*` stdout directives are consumed, dependency `cargo:rustc-link-search` outputs are replayed downstream, and direct dependency `links` metadata is consumed
`_build_script_inputs`	list<string>	resolver-owned	`[]`	Generated package source inputs made available to its Cargo build script
`package_name`	string	no	target name	Original Cargo package name when lowered from Cargo metadata
`version`	string	no	empty	Resolved Cargo package version when lowered from Cargo metadata
`source`	string	no	empty	Cargo source identifier
`checksum`	string	no	empty	Cargo.lock checksum for registry packages

Accepted but unsupported attributes: default_deps, doc_deps, doc_env, doc_link_style, doc_linker_flags, doc_named_deps, link_deps, link_style, mapped_srcs, proc_macro_deps, rpath, runtime_dependency_handling, and rustdoc_flags. Non-empty values under [target.attrs] fail validation. Use the dependency roles with the same names under [target.dependencies].

Dependency Edges#

Edge	Accepts	Description
`deps`	`rust_crate`, `rust_proc_macro`, `rust_dependency_set`, `c_provider`	Rust crate dependencies consumed by the procedural macro and C providers linked into the host plugin
`build_deps`	`rust_crate`, `rust_proc_macro`, `rust_dependency_set`, `c_provider`	Dependencies compiled for this package's Cargo build script
`proc_macro_deps`	`rust_proc_macro`	Procedural macros compiled for the execution host and passed to `rustc` through `--extern`
`link_deps`	`c_provider`	Native libraries and linker options consumed by the host plug-in

Sources#

Cargo metadata defines procedural macro targets and the host dependency information lowered into generated rust_proc_macro targets.
The Cargo lockfile defines the resolved package versions and checksums attached to those targets.
Bazel rules for Rust, Crate Universe documents the upstream pattern of generating build targets from Cargo while separating procedural macro dependencies from normal crate dependencies.

Providers#

The target emits rust_proc_macro.

Capabilities#

Capability	Output groups
`build`	`proc_macro`

Outputs#

Output	Location
Procedural macro library	`.once/out/<target>/lib<crate_name>.dylib`, `.so`, or `.dll`

Example#

toml

[[target]]
name = "identity"
kind = "rust_proc_macro"
srcs = ["src/**/*.rs"]

[target.attrs]
crate_name = "identity"
edition = "2021"