---

name: rust-reviewer description: | WHEN: Rust project review, ownership/borrowing, error handling, unsafe code, performance WHAT: Ownership patterns + Lifetime analysis + Error handling (Result/Option) + Unsafe audit + Idiomatic Rust WHEN NOT: Rust API → rust-api-reviewer, Go → go-reviewer

Rust Reviewer Skill

Purpose

Reviews Rust code for ownership, lifetimes, error handling, safety, and idiomatic patterns.

When to Use

• Rust project code review
• Ownership/borrowing review
• Lifetime annotation review
• Unsafe code audit
• Error handling patterns

Project Detection

• Cargo.toml in project root
• .rs files
• src/lib.rs or src/main.rs
• tests/ directory

Workflow

Step 1: Analyze Project

**Rust Edition**: 2021
**Type**: Library / Binary
**Dependencies**: Key crates
**Testing**: cargo test
**Linter**: clippy

Step 2: Select Review Areas

AskUserQuestion:

"Which areas to review?"
Options:
- Full Rust review (recommended)
- Ownership and borrowing
- Lifetimes and references
- Error handling (Result/Option)
- Unsafe code audit
multiSelect: true

Detection Rules

Ownership & Borrowing

Check	Recommendation	Severity
Unnecessary clone()	Borrow instead	MEDIUM
&String parameter	Use &str	MEDIUM
Vec ownership transfer	Consider slice	MEDIUM
Excessive Rc/Arc	Restructure ownership	MEDIUM

// BAD: Unnecessary clone
fn process(data: Vec<String>) {
    for item in data.clone().iter() {  // Clone not needed!
        println!("{}", item);
    }
}

// GOOD: Borrow
fn process(data: &[String]) {
    for item in data {
        println!("{}", item);
    }
}

// BAD: &String parameter
fn greet(name: &String) {
    println!("Hello, {}", name);
}

// GOOD: &str parameter (more flexible)
fn greet(name: &str) {
    println!("Hello, {}", name);
}

// BAD: Taking ownership unnecessarily
fn sum(numbers: Vec<i32>) -> i32 {
    numbers.iter().sum()
}

// GOOD: Borrow slice
fn sum(numbers: &[i32]) -> i32 {
    numbers.iter().sum()
}

Lifetimes

Check	Recommendation	Severity
Missing lifetime annotation	Add explicit lifetime	HIGH
'static overuse	Use specific lifetime	MEDIUM
Lifetime in struct	Consider ownership	MEDIUM
Complex lifetime bounds	Simplify if possible	LOW

// BAD: Missing lifetime
struct Parser {
    input: &str,  // Error: missing lifetime
}

// GOOD: Explicit lifetime
struct Parser<'a> {
    input: &'a str,
}

impl<'a> Parser<'a> {
    fn new(input: &'a str) -> Self {
        Parser { input }
    }

    fn parse(&self) -> Result<Ast<'a>, Error> {
        // ...
    }
}

// BAD: 'static when not needed
fn process(data: &'static str) {
    // Requires static lifetime!
}

// GOOD: Generic lifetime
fn process(data: &str) {
    // Works with any lifetime
}

// Consider: Ownership instead of lifetime
struct Config {
    name: String,  // Owned, no lifetime needed
}

Error Handling

Check	Recommendation	Severity
unwrap() in library	Return Result	HIGH
expect() without message	Add descriptive message	MEDIUM
panic! for recoverable	Return Err	HIGH
No custom error type	Define error enum	MEDIUM

// BAD: unwrap in library code
pub fn parse_config(path: &str) -> Config {
    let content = fs::read_to_string(path).unwrap();  // Will panic!
    serde_json::from_str(&content).unwrap()
}

// GOOD: Return Result
pub fn parse_config(path: &str) -> Result<Config, ConfigError> {
    let content = fs::read_to_string(path)
        .map_err(|e| ConfigError::IoError(e))?;
    serde_json::from_str(&content)
        .map_err(|e| ConfigError::ParseError(e))
}

// GOOD: Custom error type
#[derive(Debug, thiserror::Error)]
pub enum ConfigError {
    #[error("failed to read config file: {0}")]
    IoError(#[from] std::io::Error),

    #[error("failed to parse config: {0}")]
    ParseError(#[from] serde_json::Error),

    #[error("missing required field: {0}")]
    MissingField(String),
}

// BAD: expect without message
let value = map.get("key").expect("failed");

// GOOD: Descriptive expect
let value = map.get("key")
    .expect("config must contain 'key' field");

Option Handling

Check	Recommendation	Severity
if let Some + else	Use map_or/unwrap_or	LOW
Nested Options	Use and_then/flatten	MEDIUM
match for single case	Use if let	LOW

// BAD: Verbose Option handling
let result = match value {
    Some(v) => v.to_string(),
    None => "default".to_string(),
};

// GOOD: Using combinators
let result = value
    .map(|v| v.to_string())
    .unwrap_or_else(|| "default".to_string());

// Or even simpler
let result = value.map_or("default".to_string(), |v| v.to_string());

// BAD: Nested Options
let result: Option<Option<i32>> = Some(Some(42));
let value = match result {
    Some(Some(v)) => v,
    _ => 0,
};

// GOOD: Flatten
let value = result.flatten().unwrap_or(0);

// Using and_then for chaining
let value = get_user(id)
    .and_then(|user| user.profile)
    .and_then(|profile| profile.avatar)
    .map(|avatar| avatar.url);

Unsafe Code

Check	Recommendation	Severity
Unnecessary unsafe	Remove if safe alternative	HIGH
No safety comment	Document invariants	HIGH
Raw pointer dereference	Validate pointer	CRITICAL
Transmute usage	Use safe cast if possible	CRITICAL

// BAD: Unsafe without documentation
unsafe fn get_value(ptr: *const i32) -> i32 {
    *ptr
}

// GOOD: Documented unsafe
/// Gets the value at the given pointer.
///
/// # Safety
///
/// - `ptr` must be valid and properly aligned
/// - `ptr` must point to initialized memory
/// - The memory must not be mutated while this reference exists
unsafe fn get_value(ptr: *const i32) -> i32 {
    debug_assert!(!ptr.is_null(), "ptr must not be null");
    *ptr
}

// BAD: Transmute for casting
let bytes: [u8; 4] = unsafe { std::mem::transmute(value) };

// GOOD: Safe alternative
let bytes = value.to_ne_bytes();

// Encapsulating unsafe in safe API
pub struct Buffer {
    ptr: *mut u8,
    len: usize,
}

impl Buffer {
    /// Creates a new buffer. Safe because we control allocation.
    pub fn new(size: usize) -> Self {
        let ptr = unsafe { alloc(Layout::array::<u8>(size).unwrap()) };
        Self { ptr, len: size }
    }

    /// Safe accessor - bounds checked
    pub fn get(&self, index: usize) -> Option<u8> {
        if index < self.len {
            // SAFETY: index is bounds-checked above
            Some(unsafe { *self.ptr.add(index) })
        } else {
            None
        }
    }
}

Idiomatic Rust

Check	Recommendation	Severity
C-style loop	Use iterators	LOW
Manual index tracking	Use enumerate()	LOW
Return in match	Return match expression	LOW
Redundant type annotation	Use inference	LOW

// BAD: C-style loop
let mut i = 0;
while i < items.len() {
    process(&items[i]);
    i += 1;
}

// GOOD: Iterator
for item in &items {
    process(item);
}

// With index
for (i, item) in items.iter().enumerate() {
    println!("{}: {}", i, item);
}

// BAD: Redundant type
let numbers: Vec<i32> = vec![1, 2, 3];
let sum: i32 = numbers.iter().sum();

// GOOD: Type inference
let numbers = vec![1, 2, 3];
let sum: i32 = numbers.iter().sum();  // Only needed here

// BAD: Return in match arms
fn classify(n: i32) -> &'static str {
    match n {
        0 => { return "zero"; }
        _ if n > 0 => { return "positive"; }
        _ => { return "negative"; }
    }
}

// GOOD: Match as expression
fn classify(n: i32) -> &'static str {
    match n {
        0 => "zero",
        _ if n > 0 => "positive",
        _ => "negative",
    }
}

Response Template

## Rust Code Review Results

**Project**: [name]
**Rust Edition**: 2021 | **Clippy**: Enabled

### Ownership & Borrowing
| Status | File | Issue |
|--------|------|-------|
| MEDIUM | parser.rs:45 | Unnecessary clone() |

### Lifetimes
| Status | File | Issue |
|--------|------|-------|
| HIGH | cache.rs:23 | Missing lifetime on struct field |

### Error Handling
| Status | File | Issue |
|--------|------|-------|
| HIGH | lib.rs:67 | unwrap() in public function |

### Unsafe
| Status | File | Issue |
|--------|------|-------|
| CRITICAL | ffi.rs:12 | Unsafe block without safety comment |

### Recommended Actions
1. [ ] Replace clone() with borrowing
2. [ ] Add lifetime annotations to Cache struct
3. [ ] Return Result instead of panicking
4. [ ] Document all unsafe blocks with safety invariants

Best Practices

1. Ownership: Borrow when possible, clone when needed
2. Lifetimes: Explicit > implicit, owned > referenced
3. Errors: thiserror for libs, anyhow for apps
4. Unsafe: Minimize, document, encapsulate in safe API
5. Clippy: Run with cargo clippy -- -W clippy::pedantic

Integration

• rust-api-reviewer: Web framework patterns
• security-scanner: Rust security audit
• perf-analyzer: Performance profiling