feat(scanner): extract arrow functions and function expressions

.changeset/arrow-function-extraction.md

@@ -0,0 +1,48 @@
+---
+"@lytics/dev-agent-core": minor
+"@lytics/dev-agent": minor
+---
+
+feat(scanner): Extract arrow functions, function expressions, and exported constants
+
+### New Features
+
+**Arrow Function Extraction**
+- Extract arrow functions assigned to `const`/`let` variables
+- Extract function expressions assigned to variables
+- Detect React hooks automatically (`use*` naming pattern)
+- Detect async arrow functions
+
+**Exported Constant Extraction**
+- Extract exported `const` with object literal initializers (config objects)
+- Extract exported `const` with array literal initializers (static lists)
+- Extract exported `const` with call expression initializers (factories like `createContext()`)
+
+### API Changes
+
+**New DocumentType value:**
+- Added `'variable'` to `DocumentType` union
+
+**New metadata fields:**
+- `isArrowFunction?: boolean` - true for arrow functions (vs function expressions)
+- `isHook?: boolean` - true if name matches `/^use[A-Z]/` (React convention)
+- `isAsync?: boolean` - true for async functions
+- `isConstant?: boolean` - true for exported constants
+- `constantKind?: 'object' | 'array' | 'value'` - kind of constant initializer
+
+### Examples
+
+Now extracts:
+```typescript
+export const useAuth = () => { ... }           // Hook (isHook: true)
+export const fetchData = async (url) => { ... } // Async (isAsync: true)
+const validateEmail = (email: string) => ...   // Utility function
+export const API_CONFIG = { baseUrl: '...' }   // Object constant
+export const LANGUAGES = ['ts', 'js']          // Array constant
+export const AppContext = createContext({})    // Factory constant
+```
+
+### Migration
+
+No breaking changes. The new `'variable'` DocumentType is additive. Existing queries for `'function'`, `'class'`, etc. continue to work unchanged.
+

packages/core/src/scanner/README.md

@@ -56,7 +56,7 @@ Represents a single extracted code element or documentation section:
 interface Document {
   id: string;                // Unique identifier: "file:name:line"
   text: string;              // Text to embed (for vector search)
-  type: DocumentType;        // 'function' | 'class' | 'interface' | 'type' | 'method' | 'documentation'
+  type: DocumentType;        // 'function' | 'class' | 'interface' | 'type' | 'method' | 'documentation' | 'variable'
   language: string;          // 'typescript' | 'javascript' | 'markdown'
 
   metadata: {
@@ -67,6 +67,13 @@ interface Document {
     signature?: string;      // Full signature
     exported: boolean;       // Is it a public API?
     docstring?: string;      // Documentation comment
+
+    // Variable/function metadata (for type: 'variable')
+    isArrowFunction?: boolean;  // True for arrow functions
+    isHook?: boolean;           // True for React hooks (use* pattern)
+    isAsync?: boolean;          // True for async functions
+    isConstant?: boolean;       // True for exported constants
+    constantKind?: 'object' | 'array' | 'value';  // Kind of constant
   };
 }
 ```
@@ -364,8 +371,8 @@ const utilDocs = result.documents.filter(
 
 | Language | Scanner | Extracts | Status |
 |----------|---------|----------|--------|
-| TypeScript | `TypeScriptScanner` | Functions, classes, methods, interfaces, types, JSDoc | ✅ Implemented |
-| JavaScript | `TypeScriptScanner` | Functions, classes, methods, JSDoc | ✅ Implemented (via .ts scanner) |
+| TypeScript | `TypeScriptScanner` | Functions, classes, methods, interfaces, types, arrow functions, exported constants, JSDoc | ✅ Implemented |
+| JavaScript | `TypeScriptScanner` | Functions, classes, methods, arrow functions, exported constants, JSDoc | ✅ Implemented (via .ts scanner) |
 | Markdown | `MarkdownScanner` | Documentation sections, code blocks | ✅ Implemented |
 | Go | - | Functions, structs, interfaces | 🔄 Planned (tree-sitter) |
 | Python | - | Functions, classes, docstrings | 🔄 Planned (tree-sitter) |

packages/core/src/scanner/__tests__/fixtures/arrow-functions.ts

@@ -0,0 +1,109 @@
+/**
+ * Test fixtures for arrow function and function expression extraction.
+ * This file contains various patterns that should be extracted by the scanner.
+ */
+
+// Simple arrow function
+const simpleArrow = () => {
+  return 'hello';
+};
+
+// Arrow function with parameters
+const typedArrow = (name: string, age: number): string => {
+  return `${name} is ${age} years old`;
+};
+
+// Exported arrow function
+export const exportedArrow = (value: number) => value * 2;
+
+// Non-exported (private) helper
+const privateHelper = (x: number) => x + 1;
+
+// React-style hook (name starts with 'use')
+export const useCustomHook = (initialValue: string) => {
+  const value = initialValue;
+  const setValue = (newValue: string) => newValue;
+  return { value, setValue };
+};
+
+// Async arrow function
+export const fetchData = async (url: string) => {
+  const response = await fetch(url);
+  return response.json();
+};
+
+// Function expression (legacy style)
+// biome-ignore lint/complexity/useArrowFunction: Testing function expression extraction
+const legacyFunction = function (a: number, b: number) {
+  return a + b;
+};
+
+// Arrow function that calls other functions (for callee extraction)
+const composedFunction = (input: string) => {
+  const trimmed = input.trim();
+  const upper = trimmed.toUpperCase();
+  return privateHelper(upper.length);
+};
+
+/**
+ * A well-documented arrow function.
+ * This should have its JSDoc extracted.
+ */
+const documentedArrow = (param: string) => {
+  return param.toLowerCase();
+};
+
+// ============================================
+// EXPORTED CONSTANTS - Should be extracted
+// ============================================
+
+/**
+ * API configuration object.
+ * This should be extracted as an exported constant.
+ */
+export const API_CONFIG = {
+  baseUrl: '/api',
+  timeout: 5000,
+  retries: 3,
+};
+
+// Exported array constant
+export const SUPPORTED_LANGUAGES = ['typescript', 'javascript', 'python', 'go'];
+
+// Exported call expression (factory pattern)
+// biome-ignore lint/suspicious/noEmptyBlockStatements: Test fixture
+export const AppContext = (() => ({ value: null }))();
+
+// Typed exported constant
+export const THEME_CONFIG: { dark: boolean; primary: string } = {
+  dark: false,
+  primary: '#007bff',
+};
+
+// ============================================
+// NON-EXPORTED - Should NOT be extracted
+// ============================================
+// biome-ignore lint/correctness/noUnusedVariables: Test fixtures for non-extraction
+
+// Plain constant (primitive) - never extracted
+const plainConstant = 42;
+
+// Non-exported object - not extracted (only exported objects are extracted)
+const configObject = {
+  apiUrl: '/api',
+  timeout: 5000,
+};
+
+// Non-exported array - not extracted
+const colorList = ['red', 'green', 'blue'];
+
+// Suppress unused warnings - these are test fixtures
+void plainConstant;
+void configObject;
+void colorList;
+
+// Exported primitive - NOT extracted (primitives have low semantic value)
+export const API_ENDPOINT = 'https://api.example.com';
+
+// Re-exported for testing
+export { simpleArrow, typedArrow, composedFunction, documentedArrow, legacyFunction };