# Kotlin Language Guide
linthis uses **ktlint** for both linting and formatting, with optional **detekt** for additional static analysis.
## Supported File Extensions
- `.kt`
- `.kts`
## Required Tools
### Linter & Formatter: ktlint
```bash
# macOS
brew install ktlint
# Or via curl
curl -sSLO https://github.com/pinterest/ktlint/releases/download/1.0.1/ktlint
chmod a+x ktlint
# Verify installation
ktlint --version
```
### Optional: detekt (additional static analysis)
```bash
# macOS
brew install detekt
# Verify installation
detekt --version
```
## Configuration
### Basic Example
```toml
# .linthis/config.toml
[kotlin]
max_complexity = 15
excludes = ["build/**", "*.generated.kt"]
```
### Disable Specific Rules
```toml
[kotlin.rules]
disable = [
"max-line-length",
"no-wildcard-imports"
]
```
## Custom Rules
```toml
[[rules.custom]]
code = "kotlin/no-println"
pattern = "println\\s*\\("
message = "Use logging framework instead of println()"
severity = "warning"
languages = ["kotlin"]
[[rules.custom]]
code = "kotlin/no-lateinit"
pattern = "lateinit\\s+var"
message = "Consider using lazy or nullable instead of lateinit"
severity = "info"
languages = ["kotlin"]
```
## CLI Usage
```bash
# Check Kotlin files only
linthis -c --lang kotlin
# Format Kotlin files only
linthis -f --lang kotlin
```
## Ktlint Configuration
Create `.editorconfig` for ktlint:
```ini
[*.{kt,kts}]
indent_size = 4
max_line_length = 120
ktlint_code_style = ktlint_official
```
Or use ktlint-specific config file `.ktlint`:
```
disabled_rules=no-wildcard-imports
```
## Detekt Configuration
Create `detekt.yml`:
```yaml
complexity:
LongMethod:
threshold: 60
ComplexMethod:
threshold: 15
style:
MaxLineLength:
maxLineLength: 120
```
## Common Issues
### Ktlint not found
```
Warning: No kotlin linter available for kotlin files
Install: brew install ktlint
```
### Build outputs being checked
Add to excludes:
```toml
[kotlin]
excludes = ["build/**", "out/**", ".gradle/**"]
```
### Generated code
Add generated files to excludes:
```toml
[kotlin]
excludes = ["*.generated.kt", "generated/**"]
```
## Best Practices
1. **Use .editorconfig**: Standard way to configure ktlint
2. **Android projects**: Exclude generated code and build outputs
3. **Coroutines**: Be mindful of complexity in suspend functions
4. **KDoc comments**: Use KDoc for public API documentation