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# Configuration Management
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AutoRest Core provides a hierarchical configuration system that supports multiple configuration sources, view-based access patterns, and comprehensive options for customizing the code generation process. The system handles loading configurations from files, merging multiple sources, and provides a unified view for the generation pipeline.
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## Capabilities
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### Configuration View
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The primary interface for accessing resolved configuration values from multiple sources.
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```typescript { .api }
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/**
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 * Configuration view providing access to resolved configuration values
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 */
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class ConfigurationView {
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  /**
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   * Message emitter for configuration-related events
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   */
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  messageEmitter: MessageEmitter;
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  // Configuration access methods (implementation details vary)
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  // Provides unified access to all merged configuration sources
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}
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```
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### Configuration Structure
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Complete configuration interface defining all available AutoRest options.
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```typescript { .api }
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/**
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 * Complete AutoRest configuration structure
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 */
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interface AutoRestConfigurationImpl {
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  // Core input/output options
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  /** Input OpenAPI specification file(s) */
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  "input-file"?: string | string[];
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  /** Output folder for generated code */
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  "output-folder"?: string;
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  /** Base folder for resolving relative paths */
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  "base-folder"?: string;
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  // Processing control options  
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  /** Enable debug mode with verbose logging */
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  "debug"?: boolean;
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  /** Enable verbose output */
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  "verbose"?: boolean;
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  /** Format for log messages */
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  "message-format"?: string;
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  /** Clear output folder before generation */
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  "clear-output-folder"?: boolean;
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  // Plugin and extension options
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  /** Extensions to use during generation */
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  "use-extension"?: string | string[];
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  /** Additional modules to require */
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  "require"?: string | string[];
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  /** Processing directives for customization */
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  "directive"?: any[];
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  // Language-specific options
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  /** Namespace for generated code */
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  "namespace"?: string;
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  /** Package name for generated code */
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  "package-name"?: string;
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  /** Client name for generated classes */
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  "client-name"?: string;
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  /** Client-side validation options */
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  "client-side-validation"?: boolean;
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  // Advanced processing options
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  /** Override information section */
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  "override-info"?: {
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    title?: string;
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    description?: string;
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    version?: string;
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  };
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  /** License header for generated files */
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  "license-header"?: string;
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  /** Add credentials to generated client */
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  "add-credentials"?: boolean;
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  /** Payload flattening threshold */
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  "payload-flattening-threshold"?: number;
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  // Pipeline customization
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  /** Custom pipeline stages */
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  "pipeline"?: { [stage: string]: any };
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  /** Pass additional properties to generators */
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  "pass-thru"?: { [key: string]: any };
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}
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```
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**Usage Examples:**
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```typescript
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import { AutoRest } from "@microsoft.azure/autorest-core";
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const autorest = new AutoRest();
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// Basic configuration
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autorest.AddConfiguration({
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  "input-file": "petstore.json",
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  "output-folder": "./generated",
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  "namespace": "PetStore",
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  "client-name": "PetStoreClient"
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});
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// Advanced configuration with multiple inputs
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autorest.AddConfiguration({
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  "input-file": [
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    "swagger/pets.json",
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    "swagger/users.json", 
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    "swagger/orders.json"
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  ],
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  "output-folder": "./src/generated",
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  "base-folder": "./specs",
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  "clear-output-folder": true,
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  "debug": true,
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  "verbose": true,
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  "client-side-validation": true,
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  "payload-flattening-threshold": 2
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});
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// Language-specific configuration
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autorest.AddConfiguration({
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  "package-name": "my-api-client",
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  "license-header": "Copyright (c) 2023 My Company. All rights reserved.",
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  "add-credentials": true,
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  "override-info": {
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    title: "My API Client",
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    description: "Generated client for My API",
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    version: "1.0.0"
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  }
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});
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```
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### Configuration Merging
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Utility function for merging multiple configuration objects.
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```typescript { .api }
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/**
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 * Merges multiple configuration objects into a single configuration
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 * @param configs - Configuration objects to merge (later configs override earlier ones)
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 * @returns Merged configuration object
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 */
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function MergeConfigurations(...configs: AutoRestConfigurationImpl[]): AutoRestConfigurationImpl;
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```
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**Usage Examples:**
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```typescript
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import { MergeConfigurations } from "@microsoft.azure/autorest-core";
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// Base configuration
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const baseConfig = {
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  "output-folder": "./generated",
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  "clear-output-folder": true,
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  "debug": false
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};
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// Environment-specific overrides
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const devConfig = {
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  "debug": true,
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  "verbose": true,
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  "output-folder": "./dev-generated"
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};
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// Project-specific settings
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const projectConfig = {
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  "namespace": "MyProject",
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  "client-name": "MyProjectClient"
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};
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// Merge configurations (later configs override earlier ones)
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const finalConfig = MergeConfigurations(baseConfig, devConfig, projectConfig);
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console.log(finalConfig);
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// Result: {
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//   "output-folder": "./dev-generated",  // overridden by devConfig
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//   "clear-output-folder": true,         // from baseConfig
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//   "debug": true,                       // overridden by devConfig  
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//   "verbose": true,                     // from devConfig
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//   "namespace": "MyProject",            // from projectConfig
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//   "client-name": "MyProjectClient"     // from projectConfig
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// }
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```
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## Configuration Loading
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AutoRest supports loading configuration from multiple sources with a well-defined precedence order:
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### Configuration Sources (in precedence order, highest to lowest)
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1. **Programmatic Configuration**: Added via `AddConfiguration()` method
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2. **Command Line Arguments**: Specified via CLI flags
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3. **Configuration Files**: Loaded from specified config file or folder
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4. **Default Configuration**: Built-in default values
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### Configuration File Formats
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**JSON Configuration** (`.autorest.json`):
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```json
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{
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  "input-file": "swagger.json",
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  "output-folder": "./generated",
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  "namespace": "MyClient",
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  "debug": true
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}
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```
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**YAML Configuration** (`.autorest.yaml`):
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```yaml
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input-file: swagger.json
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output-folder: ./generated  
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namespace: MyClient
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debug: true
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```
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**Literate Configuration** (`.autorest.md` or `README.md`):
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````markdown
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# AutoRest Configuration
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> Input specification
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input-file: swagger.json
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> Output settings
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output-folder: ./generated
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namespace: MyClient
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> Processing options  
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debug: true
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verbose: false
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````
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### Configuration File Discovery
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AutoRest automatically discovers configuration files using this search order:
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1. **Explicit File**: If `configFileOrFolderUri` parameter specifies a file
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2. **Folder Search**: If parameter specifies a folder, search for:
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   - `.autorest.json`
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   - `.autorest.yaml` 
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   - `.autorest.md`
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   - `README.md` (with AutoRest configuration)
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3. **Parent Directory Search**: Recursively search parent directories
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4. **Home Directory**: Check user home directory for global configuration
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### Advanced Configuration Features
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**Environment Variable Expansion**:
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```json
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{
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  "output-folder": "${OUTPUT_DIR}/generated",
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  "namespace": "${PROJECT_NAME}Client"
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}
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```
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**Conditional Configuration**:
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```json
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{
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  "input-file": "swagger.json",
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  "output-folder": "./generated",
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  "directive": [
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    {
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      "where": "$.paths[*][*]",
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      "transform": "$.operationId = $.operationId + 'Async'"
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    }
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  ]
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}
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```
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**Multi-Language Configuration**:
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```json  
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{
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  "input-file": "swagger.json",
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  "csharp": {
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    "output-folder": "./generated/csharp",
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    "namespace": "MyCompany.Api"
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  },
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  "typescript": {
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    "output-folder": "./generated/typescript", 
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    "package-name": "my-api-client"
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  }
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}
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```