| name | chainsafe-rust-developer |
| description | Idiomatic Rust development at ChainSafe — implementation-level guidance for writing Rust in Forest, Mina-rs, ChainBridge Substrate, and other Rust projects. Use this skill whenever the user is writing Rust, asking how to do something in Rust, debugging Rust, picking between Rust patterns, dealing with errors via thiserror/anyhow, async/Tokio patterns, handling unwrap discipline, writing unsafe with SAFETY comments, testing with proptest or miri, or setting up Rust tooling. EVEN IF the user does not explicitly say "Rust" but the file is .rs. Triggers on "write a Rust function", "implement in Rust", "fix this Rust", "how do I X in Rust", "Tokio async", "Result and ?", "thiserror enum", "anyhow context", "unwrap or expect", "Arc<Mutex>", "spawn_blocking vs spawn", "miri test", "proptest", "cargo clippy", "rustfmt", "cargo.toml". Do NOT use for Rust architectural design (use chainsafe-rust-architect) or Rust PR review (use chainsafe-rust-reviewer). |
| metadata | {"type":"role-workflow","language":"rust","role":"developer","source":"languages/rust/developer.md","authored-via":"anthropic-skills:skill-creator (2026-05-27)"} |
Rust Developer
Idiomatic Rust at ChainSafe. Full reference: languages/rust/developer.md.
Tooling baselines
CI gates that must pass:
cargo fmt --all --check
cargo clippy --all-targets -- -D warnings
cargo build --workspace --all-targets
cargo test --workspace
cargo doc --no-deps
cargo audit
For unsafe-heavy crates: also cargo miri test.
Toolchain
Pin with rust-toolchain.toml:
[toolchain]
channel = "1.79.0"
components = ["rustfmt", "clippy"]
Dependencies
Cargo.lock committed for binaries; not for libraries published to crates.io.cargo audit in CI.cargo deny for license/source/version policy.- Workspace-level dependency declarations to keep versions consistent.
- Feature-gating. Keep
default = [] lean — heavy deps (tracing subscribers, DB drivers, codecs, dev utilities) go behind optional features. Put mocks/test vectors behind test-utils or mock gates; never leak test deps into production builds. Features must be additive (Cargo unifies them across the workspace) — a gate may add behavior, never swap it.
Error handling
use anyhow::{Context, Result};
use thiserror::Error;
#[derive(Error, Debug)]
pub enum StoreError {
#[error("key not found: {0}")]
NotFound(String),
#[error("backend failure")]
Backend(#[from] BackendError),
}
pub fn fetch(key: &str) -> Result<Data> {
let raw = read_backend(key).with_context(|| format!("reading {key}"))?;
parse(&raw).context("parsing value")
}
- Library crates: typed
thiserror errors.
- Binary crates:
anyhow::Result<T>.
? propagation. Match only when transforming.
unwrap and expect
- In tests: fine.
- In production code: require a
// SAFETY: ... comment justifying the invariant.
expect("...") over unwrap() when you do use it — message helps debugging.
Async
#[tokio::main] only in binaries.async fn in trait is stable as of 1.75; older crates use async-trait..await propagates cancellation — hold no critical invariant across an .await.spawn for async; spawn_blocking for CPU-bound. Mixing them up starves the runtime.Send + Sync + 'static bounds on spawned tasks.- Every external
.await (network, DB, cross-subsystem channel read) gets an explicit deadline via tokio::time::timeout. Bounded concurrency caps how many; this caps how long — an .await with no timeout hangs forever.
Unsafe
Every unsafe block:
// SAFETY: ... comment immediately above, explaining soundness.- Justification for choosing
unsafe over safe alternatives.
miri test where possible.
Forest's AI_POLICY.md treats unsafe as security-relevant. Expect HARD-FAIL-tier review scrutiny on PRs introducing it.
Testing
- Unit tests in
#[cfg(test)] mod tests { ... }.
- Integration tests in
tests/.
#[tokio::test] for async tests; flavor = "multi_thread" for parallel.proptest for parsers, serializers, math, crypto.cargo nextest for faster CI runs.miri for unsafe code.
Patterns
- Type-state when the protocol allows it. Encode "must call A before B" in the type system.
- Newtypes for domain types.
pub struct UserId(u64).
From / TryFrom for conversions over inherent to_* methods.Deref only for smart pointers — don't fake inheritance.- API & storage isolation. Keep
#[derive(Serialize, Deserialize)] and storage-schema concerns off domain types. Define serde/wire and DB DTOs at the boundary and map them explicitly to domain models. External edges only — not between internal modules.
Anti-patterns
unwrap() in production paths without // SAFETY: ....Box<dyn Error> returns when you could be specific.async fn that doesn't .await anything.Arc<Mutex<T>> reached for reflexively when a channel would model the problem better.unsafe without a soundness comment.- Public API leaking tokio types without a feature flag.
Related
