rust_toolchain.bzl

rust_toolchain

load("@rules_rust//rust:rust_toolchain.bzl", "rust_toolchain")

rust_toolchain(name, allocator_library, binary_ext, cargo, cargo_clippy, channel, clippy_driver,
               debug_info, default_edition, dlltool, dylib_ext, env, exec_triple,
               experimental_use_allocator_libraries_with_mangled_symbols,
               experimental_use_cc_common_link, extra_exec_rustc_flags, extra_rustc_flags,
               extra_rustc_flags_for_crate_types, global_allocator_library, iso_date, link_std_dylib,
               linker, linker_preference, linker_type, llvm_cov, llvm_lib, llvm_profdata, llvm_tools,
               lto, opt_level, per_crate_rustc_flags, require_explicit_unstable_features, rust_doc,
               rust_objcopy, rust_std, rustc, rustc_lib, rustfmt, staticlib_ext, stdlib_linkflags,
               strip_level, target_json, target_triple, version)

Declares a Rust toolchain for use.

This is for declaring a custom toolchain, eg. for configuring a particular version of rust or supporting a new platform.

Example:

Suppose the core rust team has ported the compiler to a new target CPU, called cpuX. This support can be used in Bazel by defining a new toolchain definition and declaration:

load('@rules_rust//rust:toolchain.bzl', 'rust_toolchain')

rust_toolchain(
    name = "rust_cpuX_impl",
    binary_ext = "",
    dylib_ext = ".so",
    exec_triple = "cpuX-unknown-linux-gnu",
    rust_doc = "@rust_cpuX//:rustdoc",
    rust_std = "@rust_cpuX//:rust_std",
    rustc = "@rust_cpuX//:rustc",
    rustc_lib = "@rust_cpuX//:rustc_lib",
    staticlib_ext = ".a",
    stdlib_linkflags = ["-lpthread", "-ldl"],
    target_triple = "cpuX-unknown-linux-gnu",
)

toolchain(
    name = "rust_cpuX",
    exec_compatible_with = [
        "@platforms//cpu:cpuX",
        "@platforms//os:linux",
    ],
    target_compatible_with = [
        "@platforms//cpu:cpuX",
        "@platforms//os:linux",
    ],
    toolchain = ":rust_cpuX_impl",
)

Then, either add the label of the toolchain rule to register_toolchains in the WORKSPACE, or pass it to the "--extra_toolchains" flag for Bazel, and it will be used.

To use a platform-specific linker, you can use a select() in the linker attribute:

rust_toolchain(
    name = "rust_toolchain_impl",
    # ... other attributes ...
    linker = select({
        "@platforms//os:linux": "//tools:rust-lld-linux",
        "@platforms//os:windows": "//tools:rust-lld-windows",
        "//conditions:default": "//tools:rust-lld",
    }),
)

The select() is evaluated against the target platform before the exec transition is applied, allowing platform-specific linker selection while ensuring the selected linker is built for the exec platform.

ATTRIBUTES