rust-ext-review-toolkit

A Claude Code plugin for reviewing Python extensions written in Rust with PyO3 — finding soundness bugs in unsafe code, PyO3 API misuse, GIL/lifetime discipline issues,

#[pyclass] trait-bound violations, panic-safety problems, and PyO3 version-migration debt.

Find the soundness bugs in your Rust extension before your users do.

What PyO3 prevents — and what it doesn't

PyO3's type system already eliminates most classic C-extension bug classes, so this toolkit does not scan for them:

• Manual Py_INCREF/Py_DECREF — Py<T> and Bound<'py, T> implement Drop
• Most NULL-pointer dereferences — fallible APIs return PyResult<T> / Option<T>
• Most use-after-free of Python objects — the 'py lifetime ties handles to the

interpreter

• Memory safety in safe Rust — the borrow checker

What PyO3 does not prevent — and what this toolkit is for:

• Soundness bugs inside unsafe (raw pyo3-ffi, transmute, manual buffer

protocol, C-library FFI)

• #[pyclass] trait-bound violations — non-Send/Sync fields without

unsendable

• Panics crossing the extern "C" FFI boundary
• PyResult propagation gaps — .unwrap(), .ok(), let _ =, missing ?,

exception clobbering

• Wrong handle kind — Bound vs Py vs Borrowed; legacy &PyAny
• #[pymethods] protocol mistakes — missing __traverse__/__clear__,

__richcmp__ semantics

• PyO3 version-migration debt and abi3 consistency
• Free-threaded Python (3.13t/3.14t) readiness

Installation

Marketplace install

claude plugin marketplace add clin1234/rust-ext-review-toolkit
claude plugin install rust-ext-review-toolkit@rust-ext-review-toolkit

Try it without installing

git clone https://github.com/clin1234/rust-ext-review-toolkit.git
claude --plugin-dir rust-ext-review-toolkit/plugins/rust-ext-review-toolkit

Prerequisites

• Claude Code installed and running
• Python 3.10+ for the analysis scripts
• tree-sitter and tree-sitter-rust: pip install tree-sitter tree-sitter-rust
• Optional: a Rust toolchain with cargo clippy / cargo miri / cargo expand

for deeper cross-referencing

Quick start

In a PyO3 crate:

/rust-ext-review-toolkit:health      # Quick scored dashboard
/rust-ext-review-toolkit:hotspots    # Worst functions: unsafe + panic + complexity
/rust-ext-review-toolkit:explore     # Full analysis (all agents, phased)
/rust-ext-review-toolkit:migrate     # Bound-API / free-threading / abi3 checklist

Agents

13 agents — 11 script-backed, 1 qualitative, 1 preflight.

Preflight

• rust-codegen-mapper — orientation guide: PyO3 version + features, file

classification, project-specific idioms; runs first so downstream agents triage accurately.

Safety-critical

• unsafe-block-auditor — soundness of every unsafe block; raw pyo3-ffi

calls; transmute; manual buffer protocol (the #1 agent)

• pyresult-propagation-checker — .unwrap()/.ok() on PyResult, missing

?, exception clobbering

• gil-discipline-checker — handles held across detach; nested attach;

foreign-callback GIL acquisition; free-threading declarations

• panic-safety-checker — panic-prone calls reachable from #[pymethods] /

#[pyfunction]

PyO3-specific

• pyclass-traits-checker — #[pyclass] Send/Sync/frozen/unsendable
• pyclass-protocol-checker — #[pymethods] slot signatures,

__traverse__/__clear__, __richcmp__

• module-init-checker — #[pymodule] shape, module-level static state
• lifetime-handle-checker — Bound vs Py vs Borrowed; legacy &PyAny

Compatibility, quality, parity

• pyo3-version-compat-scanner — deprecated/removed APIs by version; abi3

consistency

• rust-complexity-analyzer — complexity scoring (includes unsafe-block

density)

• git-history-analyzer — similar-bug detection, churn-based risk

prioritization

• parity-checker — behavioral divergence between a Rust extension and its

pure-Python fallback

Commands

| Command | Purpose | |---------|---------| | explore | Full analysis, phased agent groups, selectable aspects | | health | Quick scored dashboard, all agents in summary mode | | hotspots | Worst functions first — unsafe + pyresult + panic + complexity | | migrate | Bound-API migration, free-threading readiness, abi3 — checklist output |

How it works

Tree-sitter-rust parsing. Scripts parse .rs source with tree-sitter-rust — style-agnostic and robust against macro-heavy code. Tree-sitter does not expand procedural macros, so #[pyclass]/#[pymethods] analysis is syntactic inference over the attribute + struct + method shape.

Crate discovery. Auto-detects PyO3 crates: Cargo.toml with a pyo3 dependency and a cdylib, pyproject.toml with maturin or setuptools-rust, or

setup.py with setuptools_rust.RustExtension. Resolves the PyO3 version, active features, Python floor, and free-threading intent.

Classification. Every finding is tagged:

| Tag | Meaning | |-----|---------| | FIX | Soundness bug, panic across FFI on a reachable path, error swallowing that surfaces wrong data | | CONSIDER | Likely improvement; PyO3 idiom migration; free-threading readiness gap | | POLICY | Maintainer's design call (adopt abi3? target free-threading? support subinterpreters?) | | ACCEPTABLE | Noted, no action — e.g. an unsafe block with a verified // SAFETY: comment |

External tools (optional). When a Rust toolchain is present, clippy /

miri / cargo-expand / cargo metadata are used opportunistically. Never required — Tree-sitter analysis is the baseline.

Limitations

• Tree-sitter, not a compiler. Cannot expand procedural macros, resolve

trait-bound satisfaction, or do type inference. Scripts emit candidates (~20–40% false positives); agents confirm or dismiss each.

• Macro-generated code is invisible. What #[pyclass] emits is inferred

from the source-level shape, not seen directly.

• PyO3 evolves fast. API knowledge lives in version-keyed data files; the

analysis logic stays stable across PyO3 releases.

Sibling projects

| Project | Target | Parsing | |---------|--------|---------| | code-review-toolkit | Python source | ast | | cpython-review-toolkit | CPython runtime C | Regex | | cext-review-toolkit | C extensions | Tree-sitter-c | | rust-ext-review-toolkit | Rust/PyO3 extensions | Tree-sitter-rust |

Authors

Charlie Lin and Danzin.

License

MIT — see LICENSE.