rust_library

Rust library compiled with rustc.

Description

Compiles a first-party Rust library target. Direct Rust deps are passed through --extern; transitive rlibs are exposed as dependency search paths for downstream Rust targets. The default output is an rlib. Final artifact targets may set crate_type to staticlib, cdylib, or dylib. Static libraries expose Apple linkable provider fields, and Android dynamic libraries expose Android application package native-library provider fields. Use rust_mobile_library when one Rust target should emit both the Apple and Android native outputs. Use rust_test when a Rust crate should run tests through Once.

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 library 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 Native Development Kit 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	[]	Linker flags propagated to native consumers such as Apple app or framework targets
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 Application Binary Interface directory for cdylib or dylib outputs, such as arm64-v8a
android_api	int	no	23	Android platform level used to select the Android Native Development Kit clang wrapper for Android targets
android_ndk	string	no	ANDROID_NDK_HOME	Android Native Development Kit 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
crate_type	string	no	rlib	Rust crate type for the output

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 fail validation.

Dependency Edges

Edge	Accepts	Description
deps	rust_crate, rust_proc_macro, rust_dependency_set	Rust crate dependencies consumed through --extern

Providers

The target emits rust_crate, native_linkable, apple_linkable, and android_native_library. Native provider fields are populated only when the selected crate_type produces a native artifact that the consumer can use.

Provider Record

Field	Type	Meaning
rlib	string	Rlib output when crate_type = "rlib"
staticlib	string	Static library output when crate_type = "staticlib"
dylib	string	Dynamic library output when crate_type = "cdylib" or "dylib"
archive	string	Apple-linkable archive path for staticlib outputs
transitive_archives	list<string>	Archives consumed by Apple link targets
transitive_linkopts	list<string>	Native linker flags propagated to Apple link targets
transitive_data	list<string>	Runtime data from this crate and dependency crates
android_abi	string	Android Application Binary Interface for dynamic library outputs
android_native_libraries	list<record>	Direct Android native libraries with abi and path fields
transitive_android_native_libraries	list<record>	Direct and dependency Android native libraries packaged into Android applications

Capabilities

Capability	Output groups
build	library

Outputs

Output	Location
Rust library	.once/out/<target>/lib<crate_name>-<metadata>.rlib
Static library	.once/out/<target>/lib<crate_name>.a or .lib
Dynamic library	.once/out/<target>/lib<crate_name>.dylib, .so, or .dll

Example

[[target]]
name = "hello"
kind = "rust_library"
srcs = ["src/**/*.rs"]

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

For mobile shared code that needs both Apple and Android artifacts from one label, use rust_mobile_library.