Prevent adding duplicate files to the system prompt

src/core/prompts/sections/__tests__/custom-instructions.spec.ts

@@ -1605,3 +1605,120 @@ describe("Rules directory reading", () => {
 		expect(result).toBe("\n# Rules from .roorules:\nfallback content\n")
 	})
 })
+
+describe("File deduplication", () => {
+	beforeEach(() => {
+		vi.clearAllMocks()
+	})
+
+	test("should skip files with duplicate content (same content hash)", async () => {
+		// Mock directory structure with different files having identical content
+		const mockEntries = [
+			{
+				name: "file1.md",
+				isFile: () => true,
+				isSymbolicLink: () => false,
+				isDirectory: () => false,
+				parentPath: "/fake/path/.roo/rules",
+			},
+			{
+				name: "file2.md",
+				isFile: () => true,
+				isSymbolicLink: () => false,
+				isDirectory: () => false,
+				parentPath: "/fake/path/.roo/rules",
+			},
+			{
+				name: "file3.md",
+				isFile: () => true,
+				isSymbolicLink: () => false,
+				isDirectory: () => false,
+				parentPath: "/fake/path/.roo/rules",
+			},
+		]
+
+		// Mock fs operations
+		statMock.mockResolvedValueOnce({ isDirectory: () => true }) // .roo/rules exists
+		readdirMock.mockResolvedValueOnce(mockEntries)
+
+		// Mock file stats for each file
+		statMock.mockResolvedValueOnce({ isFile: () => true }) // file1.md
+		statMock.mockResolvedValueOnce({ isFile: () => true }) // file2.md
+		statMock.mockResolvedValueOnce({ isFile: () => true }) // file3.md
+
+		// Mock file content reading - file2 and file3 have identical content
+		readFileMock.mockResolvedValueOnce("unique content") // file1.md
+		readFileMock.mockResolvedValueOnce("duplicate content") // file2.md
+		readFileMock.mockResolvedValueOnce("duplicate content") // file3.md (should be skipped due to duplicate hash)
+
+		const result = await loadRuleFiles("/fake/path")
+
+		// Should include both unique contents, but duplicate content only once
+		expect(result).toContain("unique content")
+		expect(result).toContain("duplicate content")
+
+		// Count occurrences of "duplicate content" - should only appear once
+		const duplicateContentMatches = (result.match(/duplicate content/g) || []).length
+		expect(duplicateContentMatches).toBe(1)
+	})
+
+	test("should skip files with duplicate resolved paths via symlinks", async () => {
+		// Mock directory structure with symlinks pointing to the same file
+		const mockEntries = [
+			{
+				name: "original.md",
+				isFile: () => true,
+				isSymbolicLink: () => false,
+				isDirectory: () => false,
+				parentPath: "/fake/path/.roo/rules",
+			},
+			{
+				name: "symlink1.md",
+				isFile: () => false,
+				isSymbolicLink: () => true,
+				isDirectory: () => false,
+				parentPath: "/fake/path/.roo/rules",
+			},
+			{
+				name: "symlink2.md",
+				isFile: () => false,
+				isSymbolicLink: () => true,
+				isDirectory: () => false,
+				parentPath: "/fake/path/.roo/rules",
+			},
+		]
+
+		// Mock fs operations
+		statMock.mockResolvedValueOnce({ isDirectory: () => true }) // .roo/rules exists
+		readdirMock.mockResolvedValueOnce(mockEntries)
+
+		// Mock file stats
+		statMock.mockResolvedValueOnce({ isFile: () => true }) // original.md
+
+		// Mock symlink resolution - both symlinks point to original.md
+		readlinkMock.mockResolvedValueOnce("original.md") // symlink1 -> original.md
+		statMock.mockResolvedValueOnce({ isFile: () => true }) // symlink1 target
+
+		readlinkMock.mockResolvedValueOnce("original.md") // symlink2 -> original.md
+		statMock.mockResolvedValueOnce({ isFile: () => true }) // symlink2 target
+
+		// Mock file content reading
+		readFileMock.mockResolvedValueOnce("original content") // original.md
+		readFileMock.mockResolvedValueOnce("original content") // symlink1 target (should be skipped - same resolved path)
+		readFileMock.mockResolvedValueOnce("original content") // symlink2 target (should be skipped - same resolved path)
+
+		const result = await loadRuleFiles("/fake/path")
+
+		// Should only include original content once
+		expect(result).toContain("original content")
+
+		// Count occurrences of "original content" - should only appear once
+		const originalContentMatches = (result.match(/original content/g) || []).length
+		expect(originalContentMatches).toBe(1)
+	})
+
+	// Note: The deduplication functionality is tested by the two tests above.
+	// Additional integration testing would require more complex mock setup
+	// that may be brittle. The core functionality is verified by the
+	// content hash and resolved path deduplication tests.
+})

src/core/prompts/sections/custom-instructions.ts

@@ -10,6 +10,49 @@ import type { SystemPromptSettings } from "../types"
 import { LANGUAGES } from "../../../shared/language"
 import { getRooDirectoriesForCwd, getGlobalRooDirectory } from "../../../services/roo-config"
 
+/**
+ * File tracking system to prevent duplicate inclusions
+ */
+interface FileTracker {
+	resolvedPaths: Set<string>
+	contentHashes: Set<string>
+}
+
+/**
+ * Create content hash using FNV-1a algorithm (non-cryptographic, fast, cross-platform)
+ */
+function createContentHash(content: string): string {
+	let hash = 2166136261 // FNV offset basis (32-bit)
+
+	for (let i = 0; i < content.length; i++) {
+		hash ^= content.charCodeAt(i)
+		hash = Math.imul(hash, 16777619) // FNV prime (32-bit)
+	}
+
+	return (hash >>> 0).toString(16) // Convert to unsigned 32-bit hex
+}
+
+/**
+ * Check if a file should be included based on resolved path and content hash
+ */
+function shouldIncludeFile(resolvedPath: string, content: string, tracker: FileTracker): boolean {
+	// Skip if we've already included this resolved path
+	if (tracker.resolvedPaths.has(resolvedPath)) {
+		return false
+	}
+
+	// Skip if we've already included content with this hash
+	const contentHash = createContentHash(content)
+	if (tracker.contentHashes.has(contentHash)) {
+		return false
+	}
+
+	// Add to tracking sets
+	tracker.resolvedPaths.add(resolvedPath)
+	tracker.contentHashes.add(contentHash)
+	return true
+}
+
 /**
  * Safely read a file and return its trimmed content
  */
@@ -108,7 +151,10 @@ async function resolveSymLink(
 /**
  * Read all text files from a directory in alphabetical order
  */
-async function readTextFilesFromDirectory(dirPath: string): Promise<Array<{ filename: string; content: string }>> {
+async function readTextFilesFromDirectory(
+	dirPath: string,
+	tracker: FileTracker,
+): Promise<Array<{ filename: string; content: string }>> {
 	try {
 		const entries = await fs.readdir(dirPath, { withFileTypes: true, recursive: true })
 
@@ -136,6 +182,12 @@ async function readTextFilesFromDirectory(dirPath: string): Promise<Array<{ file
 							return null
 						}
 						const content = await safeReadFile(resolvedPath)
+
+						// Skip if file was already included or content is duplicate
+						if (!shouldIncludeFile(resolvedPath, content, tracker)) {
+							return null
+						}
+
 						// Use resolvedPath for display to maintain existing behavior
 						return { filename: resolvedPath, content, sortKey: originalPath }
 					}
@@ -182,15 +234,21 @@ function formatDirectoryContent(dirPath: string, files: Array<{ filename: string
  * Load rule files from global and project-local directories
  * Global rules are loaded first, then project-local rules which can override global ones
  */
-export async function loadRuleFiles(cwd: string): Promise<string> {
+export async function loadRuleFiles(cwd: string, tracker?: FileTracker): Promise<string> {
+	// Create a default tracker if none provided (for backward compatibility with tests)
+	const fileTracker = tracker || {
+		resolvedPaths: new Set<string>(),
+		contentHashes: new Set<string>(),
+	}
+
 	const rules: string[] = []
 	const rooDirectories = getRooDirectoriesForCwd(cwd)
 
 	// Check for .roo/rules/ directories in order (global first, then project-local)
 	for (const rooDir of rooDirectories) {
 		const rulesDir = path.join(rooDir, "rules")
 		if (await directoryExists(rulesDir)) {
-			const files = await readTextFilesFromDirectory(rulesDir)
+			const files = await readTextFilesFromDirectory(rulesDir, fileTracker)
 			if (files.length > 0) {
 				const content = formatDirectoryContent(rulesDir, files)
 				rules.push(content)
@@ -207,8 +265,9 @@ export async function loadRuleFiles(cwd: string): Promise<string> {
 	const ruleFiles = [".roorules", ".clinerules"]
 
 	for (const file of ruleFiles) {
-		const content = await safeReadFile(path.join(cwd, file))
-		if (content) {
+		const filePath = path.join(cwd, file)
+		const content = await safeReadFile(filePath)
+		if (content && shouldIncludeFile(filePath, content, fileTracker)) {
 			return `\n# Rules from ${file}:\n${content}\n`
 		}
 	}
@@ -220,7 +279,7 @@ export async function loadRuleFiles(cwd: string): Promise<string> {
  * Load AGENTS.md or AGENT.md file from the project root if it exists
  * Checks for both AGENTS.md (standard) and AGENT.md (alternative) for compatibility
  */
-async function loadAgentRulesFile(cwd: string): Promise<string> {
+async function loadAgentRulesFile(cwd: string, tracker: FileTracker): Promise<string> {
 	// Try both filenames - AGENTS.md (standard) first, then AGENT.md (alternative)
 	const filenames = ["AGENTS.md", "AGENT.md"]
 
@@ -251,7 +310,7 @@ async function loadAgentRulesFile(cwd: string): Promise<string> {
 
 			// Read the content from the resolved path
 			const content = await safeReadFile(resolvedPath)
-			if (content) {
+			if (content && shouldIncludeFile(resolvedPath, content, tracker)) {
 				return `# Agent Rules Standard (${filename}):\n${content}`
 			}
 		} catch (err) {
@@ -274,6 +333,12 @@ export async function addCustomInstructions(
 ): Promise<string> {
 	const sections = []
 
+	// Create file tracker to prevent duplicates
+	const fileTracker: FileTracker = {
+		resolvedPaths: new Set<string>(),
+		contentHashes: new Set<string>(),
+	}
+
 	// Load mode-specific rules if mode is provided
 	let modeRuleContent = ""
 	let usedRuleFile = ""
@@ -286,7 +351,7 @@ export async function addCustomInstructions(
 		for (const rooDir of rooDirectories) {
 			const modeRulesDir = path.join(rooDir, `rules-${mode}`)
 			if (await directoryExists(modeRulesDir)) {
-				const files = await readTextFilesFromDirectory(modeRulesDir)
+				const files = await readTextFilesFromDirectory(modeRulesDir, fileTracker)
 				if (files.length > 0) {
 					const content = formatDirectoryContent(modeRulesDir, files)
 					modeRules.push(content)
@@ -301,13 +366,17 @@ export async function addCustomInstructions(
 		} else {
 			// Fall back to existing behavior for legacy files
 			const rooModeRuleFile = `.roorules-${mode}`
-			modeRuleContent = await safeReadFile(path.join(cwd, rooModeRuleFile))
-			if (modeRuleContent) {
+			const rooModeRuleFilePath = path.join(cwd, rooModeRuleFile)
+			const rooModeContent = await safeReadFile(rooModeRuleFilePath)
+			if (rooModeContent && shouldIncludeFile(rooModeRuleFilePath, rooModeContent, fileTracker)) {
+				modeRuleContent = rooModeContent
 				usedRuleFile = rooModeRuleFile
 			} else {
 				const clineModeRuleFile = `.clinerules-${mode}`
-				modeRuleContent = await safeReadFile(path.join(cwd, clineModeRuleFile))
-				if (modeRuleContent) {
+				const clineModeRuleFilePath = path.join(cwd, clineModeRuleFile)
+				const clineModeContent = await safeReadFile(clineModeRuleFilePath)
+				if (clineModeContent && shouldIncludeFile(clineModeRuleFilePath, clineModeContent, fileTracker)) {
+					modeRuleContent = clineModeContent
 					usedRuleFile = clineModeRuleFile
 				}
 			}
@@ -350,14 +419,14 @@ export async function addCustomInstructions(
 
 	// Add AGENTS.md content if enabled (default: true)
 	if (options.settings?.useAgentRules !== false) {
-		const agentRulesContent = await loadAgentRulesFile(cwd)
+		const agentRulesContent = await loadAgentRulesFile(cwd, fileTracker)
 		if (agentRulesContent && agentRulesContent.trim()) {
 			rules.push(agentRulesContent.trim())
 		}
 	}
 
 	// Add generic rules
-	const genericRuleContent = await loadRuleFiles(cwd)
+	const genericRuleContent = await loadRuleFiles(cwd, fileTracker)
 	if (genericRuleContent && genericRuleContent.trim()) {
 		rules.push(genericRuleContent.trim())
 	}