TypeScript Transformer

/**
 * Main Parcel transformer instance
 * Exported as default export from the package
 */
const TSTypesTransformer: {
  /**
   * Loads TypeScript configuration for the transformer
   * @param config - Parcel config object with project paths and options
   * @param options - Parcel options including inputFS, outputFS, and project paths
   * @returns Promise resolving to TypeScript compiler options merged with defaults
   */
  loadConfig(config: ParcelConfig, options: ParcelOptions): Promise<CompilerOptions>;
  
  /**
   * Transforms TypeScript source files to declaration files
   * @param asset - Parcel asset object with filePath, getCode(), setCode(), setMap() methods
   * @param config - TypeScript compiler options from loadConfig
   * @param options - Parcel options with inputFS, outputFS, projectRoot, etc.
   * @param logger - Parcel logger with warn(), error(), verbose() methods
   * @returns Promise resolving to array containing the transformed asset
   */
  transform(
    asset: ParcelAsset, 
    config: CompilerOptions, 
    options: ParcelOptions, 
    logger: ParcelLogger
  ): Promise<ParcelAsset[]>;
};

/**
 * Parcel asset interface for transformer input/output
 */
interface ParcelAsset {
  filePath: string;
  type: string;
  getCode(): string;
  setCode(code: string): void;
  setMap(sourceMap: any): void;
  invalidateOnFileChange(filePath: string): void;
}

/**
 * Parcel configuration interface
 */
interface ParcelConfig {
  [key: string]: any;
}

/**
 * Parcel options interface with file system and project information
 */
interface ParcelOptions {
  inputFS: any;
  outputFS: any;
  projectRoot: string;
  [key: string]: any;
}

/**
 * Parcel logger interface for diagnostic output
 */
interface ParcelLogger {
  warn(diagnostic: any): void;
  error(diagnostic: any): void;
  verbose(message: string): void;
}

// This transformer is used internally by Parcel
// Configuration in .parcelrc:
{
  "extends": "@parcel/config-default",
  "transformers": {
    "*.ts": ["@parcel/transformer-typescript-types"]
  }
}

/**
 * TypeScript compiler options used by the transformer
 * These override user tsconfig.json settings for optimal declaration generation
 */
interface CompilerOptions {
  jsx: 'react';                    // Default JSX emit mode (users can override via tsconfig)
  moduleResolution: 'node';        // Node.js module resolution strategy
  noEmit: false;                   // Allow TypeScript to emit files
  noEmitOnError: false;            // Continue emission even with compilation errors
  declaration: true;               // Generate .d.ts declaration files
  declarationMap: true;            // Generate source maps for declaration files
  isolatedModules: false;          // Allow cross-module type analysis for optimization
  emitDeclarationOnly: true;       // Only emit .d.ts files, skip .js generation
  outFile: 'index.d.ts';          // Single output file (overridden by Parcel)
  composite: false;                // Disable TypeScript composite projects
  incremental: false;              // Disable incremental compilation (incompatible with createProgram)
  
  // Additional TypeScript options merged from user configuration
  [option: string]: any;
}