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rust-best-practices

Rust best practices. Use when reading or editing any .rs file, designing a crate's public API, choosing an error type, splitting a workspace, or writing async code on tokio. Triggers - "rust best practices", "is this idiomatic", "should this be a newtype", "anyhow or thiserror", "why does the borrow checker", "review this Rust".

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kromatv/kroma
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  • references/patterns.md8.1 KB

SKILL.md (original)

Review the instructions the agent will receive before you install.

Rust best practices

One idea underneath every rule: a wrong program should not compile. Where a project also writes TypeScript, the same table lives one language over in typescript-best-practices. Rust hands you more of that for free, so the failures move: unwrap(), a clone() that silences the borrow checker, a stringly typed API, a blocking call on the async runtime.

RuleSummary
Enums with dataModel variants as an enum carrying each variant's payload. A struct of Option fields plus a bool admits states that cannot happen.
NewtypesWrap primitives that mean something: struct UserId(Uuid), struct Seconds(u32). Two String parameters in a row swap silently; two newtypes do not.
Parse at the edgeUntrusted bytes become a typed value once, at the boundary, with serde plus validation. Inside, trust the type. Bound the body before parsing.
Errors by layerA library returns its own enum error (thiserror), a binary composes with anyhow. Never Box<dyn Error> in a public signature you own.
No unwrap in library code? propagates, let ... else returns early. expect only for an invariant, with a message naming what was violated. Tests and main may panic.
Context, not stringly errorsAdd context as you propagate (.context("reading manifest")), keep the source chain. Formatting an error into a String early throws the cause away.
Borrow in, own outTake &str, &[T], impl IntoIterator. Return the owned type. A clone() added to end a borrow argument is a design smell; restructure the scope.
Deliberate visibilitypub(crate) by default. pub is an API promise. #[non_exhaustive] on a public enum or struct that will grow.
Conversions via traitsFrom/TryFrom rather than to_thing() helpers, so ? and generic code pick them up.
Don't block the runtimeNo file, SQLite, or CPU work on an async thread: spawn_blocking. Never hold a std::sync::Mutex guard across .await.
Cancellation safetyAnything inside select! may be dropped at any await point. Long work takes a cancellation token and honours it.
Iterators over index loopsExpress the transformation. Avoid collect() into a Vec you immediately iterate.
SAFETY on unsafeEvery unsafe block carries a // SAFETY: comment stating the invariant that makes it sound. No exceptions.
Secrets never in DebugA type holding a token, key or password gets a hand-written Debug that redacts. Derived Debug leaks into every log line.
Clippy is the floorcargo clippy --workspace --all-targets clean, warnings denied in CI. A lint you disagree with is suppressed at the line, with the reason.
Real testsUnit tests beside the code, integration tests in tests/. No sleep for synchronisation. Property tests where the invariant is stateable.

Examples: references/patterns.md.

Read the project's Cargo.toml lints table and its clippy configuration before deciding a rule here does not apply.

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