Unsafe Checker Skill for Claude

Display the following ASCII art exactly as shown. Do not modify spaces or line breaks:

⚠️ **Unsafe Rust Checker Loaded**

     *  ^  *
    /◉\_~^~_/◉\
 ⚡/     o     \⚡
   '_        _'
   / '-----' \

Unsafe Rust Checker

When Unsafe is Valid

| Use Case | Example |

|----------|---------|

| FFI | Calling C functions |

| Low-level abstractions | Implementing Vec, Arc |

| Performance | Measured bottleneck with safe alternative too slow |

NOT valid: Escaping borrow checker without understanding why.

Required Documentation

// SAFETY: <why this is safe>
unsafe { ... }

/// # Safety
/// <caller requirements>
pub unsafe fn dangerous() { ... }

Quick Reference

| Operation | Safety Requirements |

|-----------|---------------------|

| *ptr deref | Valid, aligned, initialized |

| &*ptr | + No aliasing violations |

| transmute | Same size, valid bit pattern |

| extern "C" | Correct signature, ABI |

| static mut | Synchronization guaranteed |

| impl Send/Sync | Actually thread-safe |

Common Errors

| Error | Fix |

|-------|-----|

| Null pointer deref | Check for null before deref |

| Use after free | Ensure lifetime validity |

| Data race | Add proper synchronization |

| Alignment violation | Use #[repr(C)], check alignment |

| Invalid bit pattern | Use MaybeUninit |

| Missing SAFETY comment | Add // SAFETY: |

Deprecated → Better

| Deprecated | Use Instead |

|------------|-------------|

| mem::uninitialized() | MaybeUninit<T> |

| mem::zeroed() for refs | MaybeUninit<T> |

| Raw pointer arithmetic | NonNull<T>, ptr::add |

| CString::new().unwrap().as_ptr() | Store CString first |

| static mut | AtomicT or Mutex |

| Manual extern | bindgen |

FFI Crates

| Direction | Crate |

|-----------|-------|

| C → Rust | bindgen |

| Rust → C | cbindgen |

| Python | PyO3 |

| Node.js | napi-rs |

Claude knows unsafe Rust. Focus on SAFETY comments and soundness.