Toolchains

A Rust build in Bazel selects its compiler, standard library, and companion tools through a set of registered Bazel toolchains. rules_rust ships one toolchain type per companion tool so that Rust, rust-analyzer, rustfmt, and cargo can be resolved independently.

Most users register toolchains via the rust module extension (see Bzlmod) rather than declaring these rules directly. The rules below exist for users who need to define custom toolchains — for example, to point at a locally built rustc or to add a target triple that the extension doesn't cover.

Toolchain rules

• rust_toolchain — Declare a Rust compilation toolchain: the rustc binary, standard library, linker, and per-target compilation settings.
• rustfmt_toolchain — Declare a toolchain providing the rustfmt binary used by rustfmt rules.
• rust_analyzer_toolchain — Declare a toolchain providing the rust-analyzer binary and proc-macro server used by the rust_analyzer integration.
• cargo_toolchain — Declare a toolchain providing the cargo binary used by rules which run Cargo, such as cargo_build_script and crates_vendor. The rust module extension declares one in the repository of every rust_toolchain it registers and registers the two together, so Cargo always comes from the same release as rustc; the toolchain carries the same version, iso_date and channel identifiers and cargo_build_script fails when they differ. The cargo attribute of rust_toolchain is deprecated in its favor and is only consulted when no cargo_toolchain is registered.

Data rules

• rust_stdlib_filegroup — Group the files of a Rust standard library archive into a target that can be attached to a rust_toolchain via the rust_std attribute.