Code Linter

# Code Linter PRD

## Overview
Build a pluggable JavaScript/TypeScript linter that parses source code into an AST, runs configurable visitor-based lint rules, reports warnings and errors with source locations, and supports auto-fix mode that writes corrected files.

## Requirements
- JavaScript parser that builds an AST with node types: Program, FunctionDeclaration, VariableDeclaration, IfStatement, ForStatement, ReturnStatement, BinaryExpression, CallExpression, MemberExpression, and more
- Rule engine where each rule is a visitor function over specific AST node types
- Built-in rules: no-unused-vars, no-console, no-debugger, eqeqeq (=== instead of ==), no-var (prefer let/const), no-eval, max-line-length, no-empty-function, consistent-return
- Rule severity levels: off, warn, error — configurable per rule
- Auto-fix support where rules can provide fix suggestions as text replacements
- Config file (.linterrc.json) for rule settings, severity, and options
- File and directory globbing to lint multiple files at once
- Ignore patterns via .linterignore file
- Colorized terminal output: file:line:col severity message
- Exit code: 0 for clean, 1 for warnings only, 2 for errors
- Fix mode (--fix flag) that applies auto-fixes and writes corrected files to disk
- Rule documentation generator that outputs help text for each rule
- Handle files up to 10K lines
- Summary report: total files scanned, warnings, errors, auto-fixed count

## Tech Stack
- TypeScript / Node.js
- No external parser or linter libraries — raw AST parser required
- File system for reading source files and config

## Scoring Criteria
- **Functional (40%)**: Parser produces correct AST, rules detect violations, fixes apply cleanly
- **Quality (20%)**: Extensible rule architecture, accurate source locations, helpful messages
- **Fidelity (25%)**: All built-in rules work, config file respected, --fix mode writes correct output
- **Speed (15%)**: Time bonus