Rust Support

Turnkey provides Rust support with automatic dependency management.

Setup

Add to toolchain.toml:

[toolchains]
rust = {}
cargo = {}
rustdeps-gen = {}

Enable Rust dependencies in flake.nix:

turnkey.toolchains.buck2.rust = {
  enable = true;
  depsFile = ./rust-deps.toml;
};

Project Structure

my-project/
├── Cargo.toml
├── Cargo.lock
├── rust-deps.toml        # Generated by tk sync, from cargo
└── rust/
    └── mycrate/
        ├── src/
        │   └── lib.rs
        └── rules.star

Build Rules

In rules.star:

load("@prelude//rust:rust.bzl", "rust_library", "rust_binary")

rust_library(
    name = "mycrate",
    srcs = glob(["src/**/*.rs"]),
    deps = ["rustdeps//serde:serde"],
)

External Dependencies

Reference crates via the rustdeps cell:

deps = [
    "rustdeps//serde:serde",
    "rustdeps//tokio:tokio",
]

Features and Dependencies

Each vendored crate is built with the features and dependencies cargo resolves for it. tk sync records, for every crate, its package slice in rust-deps.toml: the features cargo tree reports for cargo test --workspace, and its normal dependencies resolved to exact versions, each with the platforms it applies on (one cargo tree run per platform the project builds for). Each crate's own rules.star is generated from its slice alone, so a change to one crate rebuilds only that crate and its dependents.

Declare what you need in Cargo.toml as you would for Cargo; there is nothing to repeat for Buck2, and no way to override Cargo's result: ask for a feature in the member's Cargo.toml.

• tk sync runs cargo with --locked, so Cargo.lock must match Cargo.toml. After editing a manifest by hand, run a cargo command (or tw cargo …) that updates the lock. The first run downloads the crates into ~/.cargo/registry.
• Every workspace member's Cargo.toml is a source of rust-deps.toml, so a features-only edit in a member regenerates it.
• A crate no configured platform builds (Windows-only, wasm, a build dependency) has an empty slice: its rules.star has no features or dependencies, and nothing configures it.

The rustdeps cell is a real directory, .turnkey/rustdeps, kept in line with the Nix-built cell index by tk materialize; see Managing Dependencies.

Auto-Sync

The cargo command is wrapped to auto-sync:

cargo add serde  # Triggers sync