review-rust

Rust Code Review

Arguments

• --parallel: Spawn specialized subagents per technology area
• Path: Target directory (default: current working directory)

Hard gates

Complete in order before writing Issues in the output (empty scope is allowed; fabricated findings are not).

1. Scope gate: You have an explicit list of .rs paths under review (from Step 1 or the user-provided path). Pass: List printed or "No Rust files in scope" — then stop with no Issues.
2. Compiler/linter gate: Step 3 commands were run from the crate or workspace root (Cargo.toml present); if they cannot run, one line states why (e.g. missing toolchain, no Cargo.toml, sandbox). Pass: You do not report a problem already shown as an error/warning in Step 3 output, and you do not duplicate compiler or clippy diagnostics the author must fix first.
3. Protocol gate: beagle-rust:review-verification-protocol is loaded before Step 7. Pass: Every Critical/Major finding satisfies Step 8 (and the protocol); if there are zero findings, say "Protocol applied; no issues" in the Review Summary.
4. Evidence gate (Critical/Major): For each Critical or Major item, you re-read the file at FILE:LINE with full surrounding context (not only the diff hunk). Pass: The Issue description matches observable code at that location.

Step 1: Identify Changed Files

git diff --name-only $(git merge-base HEAD main)..HEAD | grep -E '\.rs$'

Step 2: Check Rust Edition and MSRV

# Check Cargo.toml for edition and rust-version
grep -E 'edition|rust-version' Cargo.toml

# Check workspace members if workspace
grep -A 20 '\[workspace\]' Cargo.toml

Edition 2024 awareness (requires MSRV 1.85+):

If edition = "2024" is detected, the following behavioral changes apply throughout the review:

• unsafe_op_in_unsafe_fn is deny by default — unsafe operations inside unsafe fn MUST use explicit unsafe {} blocks
• extern "C" {} blocks must be unsafe extern "C" {}
• #[no_mangle] and #[export_name] must be #[unsafe(no_mangle)] and #[unsafe(export_name)]
• -> impl Trait captures ALL in-scope lifetimes by default (RPIT lifetime capture change); use + use<'a> for precise capture
• gen is a reserved keyword — code using it as an identifier must use r#gen
• ! (never type) falls back to ! instead of () — may change behavior of inferred types
• Temporaries in if let conditions and tail expressions are dropped earlier than in edition 2021
• Box<[T]> now implements IntoIterator

Record the detected edition — it affects severity calibration in Steps 3, 8, and the verification protocol.

Step 3: Verify Linter Status

CRITICAL: Run clippy and check BEFORE flagging style or correctness issues. Do NOT flag issues that clippy or the compiler already catches.

cargo clippy --all-targets --all-features -- -D warnings 2>&1 | head -50
cargo clippy -- -D clippy::perf 2>&1 | head -20
cargo check --all-targets 2>&1 | head -50

Edition 2024 note: Edition 2024 promotes several previously-warn lints to deny (notably unsafe_op_in_unsafe_fn). If clippy or cargo check already reports edition-related errors, do not duplicate those as review findings — instead note that the author must fix compiler errors first.

Step 4: Detect Technologies

# Detect tokio async runtime
grep -r "tokio" --include="Cargo.toml" -l | head -3

# Detect axum web framework
grep -r "axum" --include="Cargo.toml" -l | head -3

# Detect sqlx database
grep -r "sqlx" --include="Cargo.toml" -l | head -3

# Detect serde serialization
grep -r "serde" --include="Cargo.toml" -l | head -3

# Detect thiserror / anyhow
grep -r "thiserror\|anyhow" --include="Cargo.toml" -l | head -3

# Detect tracing
grep -r "tracing" --include="Cargo.toml" -l | head -3

# Check for test files in diff
git diff --name-only $(git merge-base HEAD main)..HEAD | grep -E '((^|/)(test|tests)/.*\.rs$)|(_test\.rs$)'

# Check for unsafe code in diff
git diff $(git merge-base HEAD main)..HEAD -- '*.rs' | grep -c 'unsafe'

# Detect async fn in traits (no async-trait crate needed since Rust 1.75)
grep -r "async-trait" --include="Cargo.toml" -l | head -3

# Detect LazyLock/LazyCell usage (replaces once_cell/lazy_static since 1.80)
grep -r "once_cell\|lazy_static" --include="Cargo.toml" -l | head -3

# Detect #[expect] lint attribute usage (stable since 1.81)
git diff $(git merge-base HEAD main)..HEAD -- '*.rs' | grep -c '#\[expect('

# Detect macro definitions in diff
git diff $(git merge-base HEAD main)..HEAD -- '*.rs' | grep -cE 'macro_rules!|#\[proc_macro|#\[derive\('

# Detect FFI code in diff
git diff $(git merge-base HEAD main)..HEAD -- '*.rs' | grep -cE 'extern "C"|#\[no_mangle\]|#\[repr\(C\)\]|bindgen|#\[unsafe\(no_mangle\)\]'

# Detect concurrency primitives (atomics, lock-free, hand-rolled sync)
git diff $(git merge-base HEAD main)..HEAD -- '*.rs' | grep -cE 'std::sync::atomic|Atomic(Bool|U?size|U?(8|16|32|64)|Ptr)|compare_exchange|fetch_(add|sub|or|and|xor|update)|UnsafeCell|unsafe impl (Send|Sync)|Ordering::(Relaxed|Acquire|Release|AcqRel|SeqCst)|atomic::fence'

# Detect concurrency test tooling
grep -rE 'loom|^miri$' --include='Cargo.toml' -l | head -3
git diff $(git merge-base HEAD main)..HEAD -- '*.rs' | grep -cE 'loom::|#\[cfg\(loom\)\]|cfg_attr\(miri'

# Detect concurrency crates
grep -rE '^crossbeam|^arc-swap|^parking_lot|^dashmap|^flurry|^haphazard|^seize|^atomic_wait' --include='Cargo.toml' -l | head -3

# Detect criterion benchmarks
grep -rE '^criterion' --include='Cargo.toml' -l | head -3
ls -d benches 2>/dev/null

# Detect proc-macro crate or trybuild
grep -rE 'proc-macro\s*=\s*true|^trybuild' --include='Cargo.toml' -l | head -3

# Detect public-surface changes (interface-design.md routing)
git diff $(git merge-base HEAD main)..HEAD -- '*.rs' | grep -cE '^\+\s*pub (trait|fn|struct|enum|mod|use)|^\+\s*impl[<\s].*Drop for'

# Detect ecosystem patterns (patterns-in-the-wild.md routing)
grep -rE '^slotmap|^petgraph|^scopeguard|^indexmap' --include='Cargo.toml' -l | head -3
git diff $(git merge-base HEAD main)..HEAD -- '*.rs' | grep -cE 'mem::replace|swap_remove|prelude'

Modern Rust detection notes:

• If async-trait is a dependency but the project uses edition 2024 or MSRV >= 1.75, flag as Informational — native async fn in traits is available and async-trait can likely be removed.
• If once_cell or lazy_static is a dependency but MSRV >= 1.80, flag as Informational — std::sync::LazyLock and std::cell::LazyCell are stable replacements.
• If #[allow(...)] is used where #[expect(...)] would be better (MSRV >= 1.81), note as Minor — #[expect] warns when the suppressed lint no longer fires, keeping suppressions clean.

Concurrency detection notes:

• If atomics (std::sync::atomic, compare_exchange, fetch_*), UnsafeCell, unsafe impl Send/Sync, or crossbeam / arc-swap / parking_lot are present in the diff, load beagle-rust:rust-code-review and consult references/concurrency-primitives.md, references/memory-ordering.md, and references/lock-free-patterns.md.
• If the diff introduces or restructures concurrency (worker pools, actor-style channels, tokio::spawn patterns, threads-vs-async choices), also consult references/concurrency-models.md for design-level review questions.
• If hand-rolled atomics / lock-free types appear with no loom dependency or no cargo +nightly miri test in CI, load beagle-rust:rust-testing-code-review and consult references/concurrency-testing.md.

Interface design / API surface detection:

• If the diff introduces or changes pub trait, pub fn, pub struct, derive impls on public types, impl Drop on owning types, or re-exports of foreign types, load beagle-rust:rust-code-review and consult references/interface-design.md for object-safety, ergonomic-impl, fallible-destructor, and hidden-contract review checks.
• If the diff uses index-pointer graphs (`Vec