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Leonardo Maldonado 0016d5cfb2 Add comprehensive Rust best practices skill with 179 rules

Includes rules for:
- Ownership and borrowing patterns
- Error handling with thiserror/anyhow
- Memory management and allocation
- API design following Rust guidelines
- Async/Tokio patterns
- Performance optimization
- Naming conventions
- Type safety
- Testing strategies
- Documentation standards
- Project structure
- Linting configuration
- Common anti-patterns to avoid

2026-01-19 10:23:19 -03:00

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lint-warn-complexity

Enable clippy::complexity for simpler code

Why It Matters

The clippy::complexity lint group identifies unnecessarily complex code that can be simplified. Complex code is harder to read, maintain, and often hides bugs. Clippy suggests cleaner alternatives.

Configuration

// In lib.rs or main.rs
#![warn(clippy::complexity)]

Or in Cargo.toml:

[lints.clippy]
complexity = "warn"

What It Catches

Unnecessary Complexity

// WARN: Overly complex boolean expression
if !(x == 0) { }  // Use: if x != 0 { }

// WARN: Manual implementation of Option::map
match option {
    Some(x) => Some(x + 1),
    None => None,
}  // Use: option.map(|x| x + 1)

// WARN: Unnecessary filter before count
iter.filter(|x| predicate(x)).count()  // Could simplify if only counting

Redundant Operations

// WARN: Redundant allocation
let s = format!("literal");  // Use: "literal".to_string() or just "literal"

// WARN: Unnecessarily complicated match
match result {
    Ok(ok) => Ok(ok),
    Err(err) => Err(err),
}  // Just use: result

// WARN: Box::new in return position
fn make_error() -> Box<dyn Error> {
    Box::new(MyError)  // Could use: MyError.into()
}

Overly Verbose Code

// WARN: bind_instead_of_map
option.and_then(|x| Some(x + 1))  // Use: option.map(|x| x + 1)

// WARN: clone_on_copy
let y = x.clone();  // Where x is Copy type, just use: let y = x;

// WARN: useless_let_if_seq
let result;
if condition {
    result = 1;
} else {
    result = 2;
}
// Use: let result = if condition { 1 } else { 2 };

Notable Lints in This Group

Lint	Simplification
`bind_instead_of_map`	Use `map` instead of `and_then(Some(...))`
`bool_comparison`	`if x == true` → `if x`
`clone_on_copy`	Remove `.clone()` for Copy types
`filter_next`	Use `.find()` instead
`option_map_unit_fn`	Use `if let` instead
`search_is_some`	Use `.any()` or `.contains()`
`unnecessary_cast`	Remove redundant casts
`useless_conversion`	Remove `.into()` when types match

Examples

// Before (complexity warnings)
fn find_positive(nums: &[i32]) -> Option<i32> {
    let filtered: Vec<_> = nums.iter()
        .cloned()
        .filter(|x| *x > 0)
        .collect();
    if filtered.len() == 0 {
        None
    } else {
        Some(filtered[0])
    }
}

// After (simplified)
fn find_positive(nums: &[i32]) -> Option<i32> {
    nums.iter()
        .copied()
        .find(|&x| x > 0)
}

Cognitive Load

Complex code isn't just longer—it's harder to understand:

// High cognitive load
let value = if x.is_some() { x.unwrap() } else { y.unwrap_or(z) };

// Lower cognitive load
let value = x.unwrap_or_else(|| y.unwrap_or(z));

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