biome-gritql

# Biome GritQL Custom Lint Rules

Create AST-based custom lint rules using Biome's GritQL plugin system.

## Quick Start

Create a rule file (`rules/no-use-effect-fetch.grit`):

```gritql
`useEffect($callback, $deps)` where {
    $callback <: contains `fetch`,
    register_diagnostic(
        span = $callback,
        message = "Don't fetch inside useEffect. Use TanStack Query instead.",
        severity = "error"
    )
}
```

Add to `biome.json`:

```json
{
  "plugins": ["./rules/no-use-effect-fetch.grit"]
}
```

Run: `bunx biome check` or any equivalent command to run linter in the codebase

## GritQL Syntax

### Basic Pattern Matching

```gritql
`pattern_to_match` where {
    register_diagnostic(
        span = $matched_var,
        message = "Your message here",
        severity = "error"  // hint | info | warn | error
    )
}
```

make sure to read documentation

- [BiomeJS Documentation](https://biomejs.dev/)
- [Blog examples](https://laulau.land/context-window-ate-your-instructions/)
- [BiomeJS GitHub Repository](https://github.com/biomejs/biome)
- [GritQL GitHub Repository](https://github.com/biomejs/gritql)

### Variables

- `$name` - captures any single node
- `$args` - captures arguments
- `$_` - wildcard (match but don't capture)

### Operators

| Operator | Meaning |
|----------|---------|
| `<:` | matches / contains |
| `<: contains` | deep contains |
| `<: r"regex"` | regex match |
| `not` | negation |
| `and` | both conditions |
| `or` | either condition |

## Common Rule Patterns

### Ban a Function Call

```gritql
`console.log($args)` where {
    register_diagnostic(
        span = $args,
        message = "Remove console.log before committing",
        severity = "warn"
    )
}
```

### Ban a Hook (React)

```gritql
`useMemo($args)` where {
    register_diagnostic(
        span = $args,
        message = "useMemo unnecessary with React Compiler. Remove it.",
        severity = "warn"
    )
}
```

### Ban Dynamic Imports

```gritql
`await import($p