unsafe-checker_skill

Overview

This skill inspects Rust code for unsafe blocks, FFI boundaries, raw pointers, and common undefined-behavior patterns. It highlights missing SAFETY comments, unsafe invariants, and risky uses of transmute, extern, repr(C), MaybeUninit, and static mut. ⚠️ **Unsafe Rust Checker Loaded** * ^ * /◉\_^_/◉
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How this skill works

The checker scans source for tokens and idioms that commonly require manual proofs: unsafe, raw pointers (*mut/*const), extern blocks, transmute, unions, repr(C), and FFI crate usage. It verifies presence and clarity of SAFETY comments, flags likely UB patterns (null deref, use-after-free, invalid bit patterns, alignment issues), and suggests safer replacements or required invariants. It also recommends FFI tooling like bindgen/cbindgen and notes when atomic or Mutex guards should replace static mut.

When to use it

• Code review of unsafe blocks or new FFI bindings.
• When writing or reviewing extern "C" functions and ABI-sensitive types.
• Refactoring low-level abstractions (Vec, Arc, custom allocators).
• Before merging changes that touch raw pointers, transmute, unions, or MaybeUninit.
• Auditing for soundness after performance-driven unsafe optimizations.

Best practices

• Always add a concise // SAFETY: or /// # Safety doc describing caller and callee obligations.
• Prefer MaybeUninit, NonNull, and safe wrappers over raw pointer arithmetic.
• Use #[repr(C)] only with explicit layout tests and documented field guarantees.
• Avoid static mut; prefer Atomics, Mutex, or thread-safe primitives.
• Validate FFI signatures with bindgen/cbindgen and runtime checks for null and alignment.

Example use cases

• Reviewing an unsafe impl for a custom collection that manipulates raw pointers.
• Validating extern "C" bindings generated by bindgen before exposing to C callers.
• Replacing mem::uninitialized() usage with MaybeUninit and documenting invariants.
• Auditing a transmute usage to confirm size and valid bit-pattern assumptions.
• Checking a library exposing FFI for proper CString lifetimes and ownership rules.