rust-code-review

Rust Code Review

Review Workflow

Follow this sequence to avoid false positives and catch edition-specific issues:

1. Check Cargo.toml — Note the Rust edition (2018, 2021, 2024) and MSRV if set. Edition 2024 introduces breaking changes to unsafe semantics, RPIT lifetime capture, temporary scoping, and ! type fallback. This determines which patterns apply. Check workspace structure if present.
2. Check dependencies — Note key crates (thiserror vs anyhow, tokio features, serde features). These inform which patterns are expected.
3. Scan changed files — Read full functions, not just diffs. Many Rust bugs hide in ownership flow across a function.
4. Check each category — Work through the checklist below, loading references as needed.
5. Verify before reporting — Complete Gates (below), including the verification-protocol gate, before submitting findings.

Gates

These steps are sequenced: do not skip ahead with “mental verification.” Each step has an objective Pass you can satisfy from files on disk and your own read path.

1. Crate context — Before relying on edition-specific checklist rows (Edition 2024, MSRV-sensitive APIs) or dependency assumptions. Pass: You opened the relevant Cargo.toml (package or workspace manifest) and can state edition and rust-version (if set) in one line.
2. Expanded read — Before reporting a Major or Critical finding. Pass: You read the full function, unsafe block, or impl / trait item that contains the cited line (not only a diff hunk).
3. Severity match — Before each finding line in the report. Pass: The Severity label matches Severity Calibration for that issue class, or you use Informational and give a one-line rationale.
4. Verification protocol — Before finalizing the report. Pass: beagle-rust:review-verification-protocol is loaded and every step in it that applies to this review is completed (do not substitute a vague “I checked”).

Output Format

Report findings as:

[FILE:LINE] ISSUE_TITLE
Severity: Critical | Major | Minor | Informational
Description of the issue and why it matters.

Quick Reference

| Issue Type | Reference | |------------|-----------| | Ownership transfers, borrowing, lifetimes, clone traps, iterators | [references/ownership-borrowing.md](references/ownership-borrowing.md) | | Lifetime variance, covariance/invariance, memory regions | [references/lifetime-variance.md](references/lifetime-variance.md) | | Result/Option handling, thiserror, anyhow, opaque vs enumerated errors, deferred-cleanup with ? | [references/error-handling.md](references/error-handling.md) | | Async pitfalls, Send/Sync bounds, poll contract, Pin mechanics, cancellation soundness | [references/async-concurrency.md](references/async-concurrency.md) | | Send/Sync semantics, atomics, memory ordering, lock patterns | [references/concurrency-primitives.md](references/concurrency-primitives.md) | | Memory ordering decision tree, fences, ABA, out-of-thin-air | [references/memory-ordering.md](references/memory-ordering.md) | | Hand-rolled spinlocks, channels, Arc, seqlock, CAS retry patterns | [references/lock-free-patterns.md](references/lock-free-patterns.md) | | Shared-memory vs worker-pool vs actor design, async vs threads, race-condition vs data race | [references/concurrency-models.md](references/concurrency-models.md) | | Type layout, alignment, repr, PhantomData, generics vs dyn Trait, wide pointers, auto-trait leakage | [references/types-layout.md](references/types-layout.md) | | Object safety, ergonomic trait impls, Deref discipline, fallible destructors, hidden contracts, is_normal | [references/interface-design.md](references/interface-design.md) | | Index pointers, drop guards, extension traits, crate preludes | [references/patterns-in-the-wild.md](references/patterns-in-the-wild.md) | | Unsafe code, API design, derive patterns, clippy patterns | [references/common-mistakes.md](references/common-mistakes.md) | | Validity vs safety, drop check, may_dangle, provenance, panic safety in unsafe, MaybeUninit, Miri | [references/unsafe-deep.md](references/unsafe-deep.md) |

For development guidance on performance, pointer types, type state, clippy config, iterators, generics, and documentation, use the beagle-rust:rust-best-practices skill.

Review Checklist

Ownership and Borrowing

• [ ] No unnecessary .clone() to silence the borrow checker (hiding design issues)
• [ ] No .clone() inside loops — prefer .cloned() or .copied() on iterators
• [ ] No cloning to avoid lifetime annotations (take ownership explicitly or restructure)
• [ ] References have appropriate lifetimes (not overly broad 'static when shorter lifetime works)
• [ ] Edition 2024: RPIT (-> impl Trait) captures all in-scope lifetimes by default; use + use<'a> for precise capture control
• [ ] &str preferred over String, &[T] over Vec<T> in function parameters
• [ ] impl AsRef<T> or Into<T> used for flexible API parameters
• [ ] No dangling references or use-after-move
• [ ] Interior mutability (Cell, RefCell, Mutex) used only when shared mutation is genuinely needed
• [ ] Small types (≤24 bytes) derive Copy and are passed by value
• [ ] Cow<'_, T> used when ownership is ambiguous
• [ ] Iterator chains preferred over index-based loops for collection transforms
• [ ] No premature .collect() — pass iterators directly when the consumer accepts them
• [ ] .sum() preferred over .fold() for summation (compiler optimizes better)
• [ ] _or_else variants used when fallbacks involve allocation
• [ ] Edition 2024: if let temporaries drop at end of the if let — code relying on temporaries living through the else branch needs restructuring
• [ ] Edition 2024: Box<[T]> implements IntoIterator — prefer direct iteration over into_vec() first

Error Handling

• [ ] Result<T, E> used for recoverable errors, not panic!/unwrap/expect
• [ ] Error types provide context (thiserror with #[error("...")] or manual Display)
• [ ] ? operator used with proper From implementations or .map_err()
• [ ] unwrap() / expect() only in tests, examples, or provably-safe contexts
• [ ] Error variants are specific enough to be actionable by callers
• [ ] anyhow used in applications, thiserror in libraries (or clear rationale for alternatives)
• [ ] _or_else variants used when fallbacks involve allocation (ok_or_else, unwrap_or_else)
• [ ] let-else used for early returns on failure (let Ok(x) = expr else { return ... })
• [ ] inspect_err used for error logging, map_err for error transformation

Traits and Types

• [ ] Traits are minimal and cohesive (single responsibility)
• [ ] derive macros appropriate for the type (Clone, Debug, PartialEq used correctly)
• [ ] Newtypes used to prevent primitive obsession (e.g., struct UserId(Uuid) not bare Uuid)
• [ ] From/Into implementations are lossless and infallible; TryFrom for fallible conversions
• [ ] Sealed traits used when external implementations shouldn't be allowed
• [ ] Default implementations provided where they make sense
• [ ] Send + Sync bounds verified for types shared across threads
• [ ] #[diagnostic::on_unimplemented] used on public traits to provide clear error messages when users forget to implement them

Interface Design

Detailed guidance: [references/interface-design.md](references/interface-design.md)

• [ ] Methods on dyn-intended traits don't use Self by value, generic params, or associated constants (or are gated where Self: Sized)
• [ ] New traits ship with blanket impls for &T, &mut T, Box<T> so reference and smart-pointer arguments work
• [ ] Iterable types implement IntoIterator for &Self and &mut Self, not just Self
• [ ] Deref only used for transparent forwarding, never as "inheritance" — inherent-method ambiguity is a real bug class
• [