Rust Bazel Starter

# This is executable Markdown that's tested on CI.
# How is that possible? See https://gist.github.com/bwoods/1c25cb7723a06a076c2152a2781d4d49
set -o errexit -o nounset -o xtrace
alias ~~~=":<<'~~~sh'";:<<'~~~sh'

This repo includes:

• 🧱 Latest version of Bazel and dependencies
• 📦 Curated bazelrc flags via [bazelrc-preset.bzl]
• 🧰 Developer environment setup with [bazel_env.bzl]
• 🎨 rustfmt and clippy using rules_lint
• ✅ Pre-commit hooks for automatic linting and formatting
• 📚 Cargo package manager integration

Note

You can customize languages and features with the interactive wizard in the aspect init command. init is an alternative to this starter repo, which was generated using the 'rust' preset. See https://docs.aspect.build/cli/overview

Setup dev environment

First, we recommend you setup a Bazel-based developer environment with direnv.

1. install https://direnv.net/docs/installation.html
2. run direnv allow and follow the prompts to bazel run //tools:bazel_env

This isn't strictly required, but the commands which follow assume that needed tools are on the PATH, so skipping direnv means you're responsible for installing them yourself.

Try it out

First we create a tiny Rust program with a third-party dependency:

cargo new hello_world
cat >hello_world/src/main.rs <<EOF
use rand::Rng;

fn main() {
    let num = rand::thread_rng().gen_range(1..=3);
    for _ in 0..num {
        println!("Hello from Rust");
    }
}
EOF

Add the dependency to Cargo.toml, and run check to update the Cargo.lock file that Bazel reads:

echo 'rand = "0.8"' >> hello_world/Cargo.toml
cargo check

We don't have any BUILD file generation for Rust yet, so you're forced to create it manually.

touch hello_world/BUILD
buildozer 'new_load @rules_rust//rust:defs.bzl rust_binary' hello_world:__pkg__
buildozer 'new rust_binary hello_world' hello_world:__pkg__
buildozer 'add srcs src/main.rs' hello_world:hello_world
buildozer 'add deps @crates//:rand' hello_world:hello_world

Now you can run the program and assert that it produces the expected output.

output="$(bazel run hello_world | tail -1)"

[ "${output}" = "Hello from Rust" ] || {
    echo >&2 "Wanted output 'Hello from Rust' but got '${output}'"
    exit 1
}

Formatting

We can format the code with rustfmt. Let's create some intentionally poorly formatted code (the indentation is wrong) and also an auto-fixable print_literal warning from Clippy.

cat >hello_world/src/main.rs <<EOF
fn main(){
println!("{}", "Hello from Rust");
}
EOF

Now format it:

format

And run the linter in auto-fix mode:

aspect lint --fix

Let's verify the code was fixed:

cat hello_world/src/main.rs
# -> fn main() {
# ->     println!("Hello from Rust");
# -> }