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# Code Formatting
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Prettier integration with automatic configuration discovery and file-first configuration precedence for consistent code formatting.
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## Capabilities
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### lb-prettier Command
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Runs Prettier with automatic configuration discovery and sensible defaults.
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```typescript { .api }
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/**
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 * Prettier formatter function with configuration discovery
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 * @param argv - Command line arguments including files and options
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 * @param options - Execution options for dry run and process control
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 * @returns ChildProcess when executed, string when dry run
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 */
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function prettier(argv: string[], options?: RunOptions): ChildProcess | string;
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```
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**CLI Usage:**
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```bash
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# Format files
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lb-prettier "**/*.ts" "**/*.js"
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# Check formatting without changes
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lb-prettier --check "**/*.ts"
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# List files that would be formatted
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lb-prettier --list-different "**/*.ts"
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# Write formatted files
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lb-prettier --write "**/*.ts" "**/*.js"
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# Format specific files
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lb-prettier src/index.ts src/utils.ts
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```
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**Programmatic Usage:**
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```typescript
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import { prettier } from "@loopback/build";
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// Format TypeScript files
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const child = prettier(["--write", "**/*.ts"]);
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// Dry run to see command
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const command = prettier(["--check", "src/"], { dryRun: true });
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console.log(command); // Shows the Prettier command that would be executed
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// Format with custom working directory
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prettier(["--write", "src/"], { cwd: "/path/to/project" });
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```
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### Configuration Discovery
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Automatically discovers Prettier configuration files with file-first precedence.
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**Configuration Search Order:**
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1. Project-specific configuration (if `--config`, `--no-config`, or `--find-config-path` not provided)
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2. `.prettierrc` in project root
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3. Falls back to `@loopback/build/config/.prettierrc`
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**Configuration Precedence:**
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Uses `--config-precedence prefer-file` to prioritize project configuration files over CLI options.
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### Default Configuration
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Provides sensible defaults for LoopBack and TypeScript projects.
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```typescript { .api }
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// @loopback/build/config/.prettierrc contents:
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interface PrettierConfig {
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  bracketSpacing: false;    // {foo} instead of { foo }
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  singleQuote: true;        // 'string' instead of "string"
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  printWidth: 80;           // Line wrap at 80 characters
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  trailingComma: "all";     // Trailing commas everywhere
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  arrowParens: "avoid";     // x => x instead of (x) => x
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}
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```
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### File Pattern Support
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Supports glob patterns and specific file targeting.
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```typescript { .api }
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// Glob patterns for multiple files
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// Specific file paths
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// Supports all file types that Prettier handles
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```
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**Common File Patterns:**
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```bash
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# TypeScript and JavaScript
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lb-prettier "**/*.{ts,js}"
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# All supported formats
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lb-prettier "**/*.{ts,js,json,md,yml,yaml}"
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# Specific directories
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lb-prettier "src/**/*.ts" "test/**/*.ts"
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```
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### Command Line Option Passthrough
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All Prettier command line options are supported and passed through.
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```typescript { .api }
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interface PrettierOptions {
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  "--write": boolean;              // Write formatted files to disk
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  "--check": boolean;              // Check if files are formatted
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  "--list-different": boolean;     // List files that differ from Prettier formatting
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  "--config": string;              // Path to configuration file
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  "--no-config": boolean;          // Do not look for configuration file
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  "--find-config-path": string;    // Find and return path to configuration file
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  "--ignore-path": string;         // Path to ignore file
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  "--no-ignore": boolean;          // Do not look for ignore files
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  "--with-node-modules": boolean;  // Process files in node_modules
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  "--parser": string;              // Parser to use (auto-detected by default)
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  "--print-width": number;         // Line wrap width
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  "--tab-width": number;           // Tab width
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  "--use-tabs": boolean;           // Use tabs instead of spaces
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  "--semi": boolean;               // Print semicolons
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  "--single-quote": boolean;       // Use single quotes
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  "--quote-props": string;         // Quote object properties
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  "--jsx-single-quote": boolean;   // Use single quotes in JSX
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  "--trailing-comma": string;      // Trailing comma policy
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  "--bracket-spacing": boolean;    // Print spaces inside object brackets
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  "--bracket-same-line": boolean;  // Put closing bracket on same line
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  "--arrow-parens": string;        // Arrow function parentheses policy
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  "--range-start": number;         // Format from this character
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  "--range-end": number;           // Format to this character
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  "--stdin-filepath": string;      // File path for stdin input
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  "--end-of-line": string;         // Line ending style
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}
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```
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### Usage Examples
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**Basic Formatting:**
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```typescript
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import { prettier } from "@loopback/build";
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// Format all TypeScript files
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prettier(["--write", "**/*.ts"], { dryRun: false });
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// Check formatting without changes
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prettier(["--check", "src/"], { dryRun: false });
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```
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**Package.json Integration:**
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```json
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{
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  "scripts": {
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    "prettier:cli": "lb-prettier \"**/*.ts\" \"**/*.js\"",
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    "prettier:check": "npm run prettier:cli -- --list-different",
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    "prettier:fix": "npm run prettier:cli -- --write",
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    "format": "npm run prettier:fix"
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  }
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}
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```
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**Custom Configuration:**
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```bash
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# Use custom config file
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lb-prettier --config .prettierrc.custom.json --write "**/*.ts"
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# Ignore configuration files
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lb-prettier --no-config --write --single-quote "**/*.ts"
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# Custom ignore file
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lb-prettier --ignore-path .prettierignore.custom --write "**/*.ts"
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```
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### Integration with Other Tools
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Works seamlessly with ESLint and other development tools.
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**ESLint Integration:**
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- LoopBack ESLint config is compatible with default Prettier settings
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- No conflicting rules between ESLint and Prettier formatting
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**Editor Integration:**
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- Configuration files are automatically detected by editors
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- Supports format-on-save workflows
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- Compatible with VS Code, WebStorm, and other editors
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### Error Handling
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Prettier errors are properly handled and reported.
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```typescript { .api }
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// Syntax errors in files are reported with file location
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// Configuration errors show helpful error messages  
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// Process exits with non-zero code on formatting errors (when using --check)
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// Invalid file patterns are reported clearly
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```