cargo-fl

Lightning-fast Rust linter that runs without compilation. Similar to ruff for Python, but for Rust.

fl = fast lint. Because developer time is precious.

Features

• < 1 second on large codebases (100k+ lines)
• Zero compilation - pure AST analysis using syn
• Parallel processing with rayon
• Auto-fix support for common issues
• Configurable rules via .fl.toml
• LSP Server for real-time editor feedback
• VSCode Extension for seamless integration

Installation

cargo install cargo-fl

Usage

Command Line

# Lint current directory
cargo fl check

# Lint specific path
cargo fl check src/

# Auto-fix issues
cargo fl check --fix

# Different output formats
cargo fl check --format json
cargo fl check --format github  # For CI

# Strict mode (exit 1 on issues)
cargo fl check --strict

Configuration

Generate a default config:

cargo fl config --init

This creates .fl.toml:

[rules]
enable_all = true
disable = ["specific_rule"]

[severity]
unused_imports = "warning"
missing_docs = "info"

Editor Integration

VSCode

1. Install the cargo-fl VSCode extension
2. The extension will automatically use the LSP server for real-time feedback

Other Editors

Use the LSP server directly:

cargo-fl-lsp

The LSP server supports:

• Real-time diagnostics
• Code actions (auto-fixes)
• Configuration via .fl.toml

Rules

Core Quality Rules

• unwrap_usage: Detects .unwrap(), .unwrap_unchecked(), and .expect() calls
• todo_macros: Finds todo!(), unimplemented!(), unreachable!(), and panic!() macros
• must_use: Identifies unused results from functions with #[must_use] return types
• anti_patterns: Common Rust anti-patterns and code smells

Style & Structure Rules

• unused_imports: Detects unused import statements
• missing_docs: Missing documentation for public items
• line_length: Lines exceeding configured character limit
• naming_convention: Rust naming convention violations

Complexity Rules

• cyclomatic_complexity: Functions with high cyclomatic complexity
• cognitive_complexity: Functions with high cognitive load
• unsafe_code: Unsafe code block warnings

Import & Organization

• import_order: Incorrect import statement ordering
• syntax_errors: Basic syntax validation

Performance

Typical performance on a 100k line Rust codebase:

• Analysis: < 1 second
• Memory usage: < 100MB
• Parallel processing across CPU cores

Contributing

1. Fork the repository
2. Create a feature branch
3. Make changes with tests
4. Submit a pull request

License

MIT OR Apache-2.0