fix: Ensure filename is available for diff rendering in write-file

This commit resolves a bug where the `write-file` operation could fail to render content due to a missing filename.

The fix involves:
- Ensuring `fileName` is consistently passed to `DiffRenderer.tsx` through `ToolConfirmationMessage.tsx`, `ToolMessage.tsx`, and `useGeminiStream.ts`.
- Modifying `edit.ts` and `write-file.ts` to include `fileName` in the `FileDiff` object.
- Expanding the `FileDiff` interface in `tools.ts` to include `fileName`.

Additionally, this commit enhances the diff rendering by:
- Adding syntax highlighting based on file extension in `DiffRenderer.tsx`.
- Adding more language mappings to `getLanguageFromExtension` in `DiffRenderer.tsx`.
- Added lots of tests for all the above.

Fixes https://b.corp.google.com/issues/418125982

.github/workflows/ci.yml

@@ -38,12 +38,12 @@ jobs:
       - name: Run linter
         run: npm run lint
 
-      - name: Run type check
-        run: npm run typecheck
-
       - name: Build project
         run: npm run build
 
+      - name: Run type check
+        run: npm run typecheck
+
       - name: Upload build artifacts
         uses: actions/upload-artifact@v4
         with:

package-lock.json

@@ -4477,6 +4477,24 @@
         "react": ">=18.0.0"
       }
     },
+    "node_modules/ink-testing-library": {
+      "version": "4.0.0",
+      "resolved": "https://registry.npmjs.org/ink-testing-library/-/ink-testing-library-4.0.0.tgz",
+      "integrity": "sha512-yF92kj3pmBvk7oKbSq5vEALO//o7Z9Ck/OaLNlkzXNeYdwfpxMQkSowGTFUCS5MSu9bWfSZMewGpp7bFc66D7Q==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">=18"
+      },
+      "peerDependencies": {
+        "@types/react": ">=18.0.0"
+      },
+      "peerDependenciesMeta": {
+        "@types/react": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/ink-text-input": {
       "version": "6.0.0",
       "resolved": "https://registry.npmjs.org/ink-text-input/-/ink-text-input-6.0.0.tgz",
@@ -8156,6 +8174,7 @@
         "@types/react": "^18.3.1",
         "@types/shell-quote": "^1.7.5",
         "@types/yargs": "^17.0.32",
+        "ink-testing-library": "^4.0.0",
         "jsdom": "^26.1.0",
         "typescript": "^5.3.3",
         "vitest": "^3.1.1"

package.json

@@ -16,7 +16,7 @@
     "debug": "NODE_ENV=development DEBUG=1 scripts/start.sh",
     "lint:fix": "eslint . --fix",
     "lint": "eslint . --ext .ts,.tsx",
-    "typecheck": "tsc --noEmit --jsx react-jsx",
+    "typecheck": "npm run typecheck --workspaces --if-present",
     "format": "prettier --write .",
     "preflight": "npm run format --workspaces --if-present && npm run lint && npm run test --workspaces --if-present",
     "auth:npm": "npx google-artifactregistry-auth",

packages/cli/package.json

@@ -19,6 +19,7 @@
     "format": "prettier --write .",
     "test": "vitest run",
     "test:ci": "vitest run --reporter=junit --outputFile=junit.xml",
+    "typecheck": "tsc --noEmit",
     "prerelease:version": "node ../../scripts/bind_package_version.js",
     "prerelease:deps": "node ../../scripts/bind_package_dependencies.js",
     "prepublishOnly": "npm publish --workspace=@gemini-code/server",
@@ -52,6 +53,7 @@
     "@types/react": "^18.3.1",
     "@types/shell-quote": "^1.7.5",
     "@types/yargs": "^17.0.32",
+    "ink-testing-library": "^4.0.0",
     "jsdom": "^26.1.0",
     "typescript": "^5.3.3",
     "vitest": "^3.1.1"

packages/cli/src/ui/components/messages/DiffRenderer.test.tsx

@@ -0,0 +1,117 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { render } from 'ink-testing-library';
+import { DiffRenderer } from './DiffRenderer.js';
+import * as CodeColorizer from '../../utils/CodeColorizer.js';
+import { vi } from 'vitest';
+
+describe('<DiffRenderer />', () => {
+  const mockColorizeCode = vi.spyOn(CodeColorizer, 'colorizeCode');
+
+  beforeEach(() => {
+    mockColorizeCode.mockClear();
+  });
+
+  it('should call colorizeCode with correct language for new file with known extension', () => {
+    const newFileDiffContent = `
+diff --git a/test.py b/test.py
+new file mode 100644
+index 0000000..e69de29
+--- /dev/null
++++ b/test.py
+@@ -0,0 +1 @@
++print("hello world")
+`;
+    render(
+      <DiffRenderer diffContent={newFileDiffContent} filename="test.py" />,
+    );
+    expect(mockColorizeCode).toHaveBeenCalledWith(
+      'print("hello world")',
+      'python',
+    );
+  });
+
+  it('should call colorizeCode with null language for new file with unknown extension', () => {
+    const newFileDiffContent = `
+diff --git a/test.unknown b/test.unknown
+new file mode 100644
+index 0000000..e69de29
+--- /dev/null
++++ b/test.unknown
+@@ -0,0 +1 @@
++some content
+`;
+    render(
+      <DiffRenderer diffContent={newFileDiffContent} filename="test.unknown" />,
+    );
+    expect(mockColorizeCode).toHaveBeenCalledWith('some content', null);
+  });
+
+  it('should call colorizeCode with null language for new file if no filename is provided', () => {
+    const newFileDiffContent = `
+diff --git a/test.txt b/test.txt
+new file mode 100644
+index 0000000..e69de29
+--- /dev/null
++++ b/test.txt
+@@ -0,0 +1 @@
++some text content
+`;
+    render(<DiffRenderer diffContent={newFileDiffContent} />);
+    expect(mockColorizeCode).toHaveBeenCalledWith('some text content', null);
+  });
+
+  it('should render diff content for existing file (not calling colorizeCode directly for the whole block)', () => {
+    const existingFileDiffContent = `
+diff --git a/test.txt b/test.txt
+index 0000001..0000002 100644
+--- a/test.txt
++++ b/test.txt
+@@ -1 +1 @@
+-old line
++new line
+`;
+    const { lastFrame } = render(
+      <DiffRenderer
+        diffContent={existingFileDiffContent}
+        filename="test.txt"
+      />,
+    );
+    // colorizeCode is used internally by the line-by-line rendering, not for the whole block
+    expect(mockColorizeCode).not.toHaveBeenCalledWith(
+      expect.stringContaining('old line'),
+      expect.anything(),
+    );
+    expect(mockColorizeCode).not.toHaveBeenCalledWith(
+      expect.stringContaining('new line'),
+      expect.anything(),
+    );
+    const output = lastFrame();
+    const lines = output!.split('\n');
+    expect(lines[0]).toBe('1 - old line');
+    expect(lines[1]).toBe('1 + new line');
+  });
+
+  it('should handle diff with only header and no changes', () => {
+    const noChangeDiff = `diff --git a/file.txt b/file.txt
+index 1234567..1234567 100644
+--- a/file.txt
++++ b/file.txt
+`;
+    const { lastFrame } = render(
+      <DiffRenderer diffContent={noChangeDiff} filename="file.txt" />,
+    );
+    expect(lastFrame()).toContain('No changes detected');
+    expect(mockColorizeCode).not.toHaveBeenCalled();
+  });
+
+  it('should handle empty diff content', () => {
+    const { lastFrame } = render(<DiffRenderer diffContent="" />);
+    expect(lastFrame()).toContain('No diff content');
+    expect(mockColorizeCode).not.toHaveBeenCalled();
+  });
+});

packages/cli/src/ui/components/messages/DiffRenderer.tsx

@@ -105,6 +105,14 @@ export const DiffRenderer: React.FC<DiffRendererProps> = ({
 
   const parsedLines = parseDiffWithLineNumbers(diffContent);
 
+  if (parsedLines.length === 0) {
+    return (
+      <Box borderStyle="round" borderColor={Colors.SubtleComment} padding={1}>
+        <Text dimColor>No changes detected.</Text>
+      </Box>
+    );
+  }
+
   // Check if the diff represents a new file (only additions and header lines)
   const isNewFile = parsedLines.every(
     (line) =>
@@ -233,16 +241,21 @@ const renderDiffContent = (
 
 const getLanguageFromExtension = (extension: string): string | null => {
   const languageMap: { [key: string]: string } = {
-    '.js': 'javascript',
+    js: 'javascript',
-    '.ts': 'typescript',
+    ts: 'typescript',
-    '.py': 'python',
+    py: 'python',
-    '.json': 'json',
+    json: 'json',
-    '.css': 'css',
+    css: 'css',
-    '.html': 'html',
+    html: 'html',
-    '.sh': 'bash',
+    sh: 'bash',
-    '.md': 'markdown',
+    md: 'markdown',
-    '.yaml': 'yaml',
+    yaml: 'yaml',
-    '.yml': 'yaml',
+    yml: 'yaml',
+    txt: 'plaintext',
+    java: 'java',
+    c: 'c',
+    cpp: 'cpp',
+    rb: 'ruby',
   };
   return languageMap[extension] || null; // Return null if extension not found
 };

packages/cli/src/ui/components/messages/ToolConfirmationMessage.tsx

@@ -52,7 +52,12 @@ export const ToolConfirmationMessage: React.FC<
   if (isEditDetails(confirmationDetails)) {
     // Body content is now the DiffRenderer, passing filename to it
     // The bordered box is removed from here and handled within DiffRenderer
-    bodyContent = <DiffRenderer diffContent={confirmationDetails.fileDiff} />;
+    bodyContent = (
+      <DiffRenderer
+        diffContent={confirmationDetails.fileDiff}
+        filename={confirmationDetails.fileName}
+      />
+    );
 
     question = `Apply this change?`;
     options.push(

packages/cli/src/ui/components/messages/ToolMessage.tsx

@@ -90,7 +90,10 @@ export const ToolMessage: React.FC<ToolMessageProps> = ({
               </Box>
             )}
             {typeof displayableResult === 'object' && (
-              <DiffRenderer diffContent={displayableResult.fileDiff} />
+              <DiffRenderer
+                diffContent={displayableResult.fileDiff}
+                filename={displayableResult.fileName}
+              />
             )}
             {hiddenLines > 0 && (
               <Box>

packages/cli/src/ui/hooks/atCommandProcessor.ts

@@ -154,7 +154,9 @@ export async function handleAtCommand({
     if (isNodeError(error) && error.code === 'ENOENT') {
       onDebugMessage(`Path not found, proceeding with original: ${pathSpec}`);
     } else {
-      console.error(`Error stating path ${pathPart}:`, error);
+      console.error(
+        `Error stating path ${pathPart}: ${getErrorMessage(error)}`,
+      );
       onDebugMessage(
         `Error stating path, proceeding with original: ${pathSpec}`,
       );
@@ -200,7 +202,7 @@ export async function handleAtCommand({
     );
 
     return { processedQuery, shouldProceed: true };
-  } catch (error) {
+  } catch (error: unknown) {
     // Handle errors during tool execution
     toolCallDisplay = {
       callId: `client-read-${userMessageTimestamp}`,

packages/cli/src/ui/hooks/useCompletion.ts

@@ -7,7 +7,12 @@
 import { useState, useEffect, useCallback } from 'react';
 import * as fs from 'fs/promises';
 import * as path from 'path';
-import { isNodeError, escapePath, unescapePath } from '@gemini-code/server';
+import {
+  isNodeError,
+  escapePath,
+  unescapePath,
+  getErrorMessage,
+} from '@gemini-code/server';
 import {
   MAX_SUGGESTIONS_TO_SHOW,
   Suggestion,
@@ -202,7 +207,7 @@ export function useCompletion(
           setActiveSuggestionIndex(filteredSuggestions.length > 0 ? 0 : -1);
           setVisibleStartIndex(0);
         }
-      } catch (error) {
+      } catch (error: unknown) {
         if (isNodeError(error) && error.code === 'ENOENT') {
           // Directory doesn't exist, likely mid-typing, clear suggestions
           if (isMounted) {
@@ -211,8 +216,7 @@ export function useCompletion(
           }
         } else {
           console.error(
-            `Error fetching completion suggestions for ${baseDirAbsolute}:`,
+            `Error fetching completion suggestions for ${baseDirAbsolute}: ${getErrorMessage(error)}`,
-            error,
           );
           if (isMounted) {
             resetCompletionState();

packages/cli/src/ui/hooks/useGeminiStream.ts

@@ -326,6 +326,7 @@ export const useGeminiStream = (
       if ('fileDiff' in originalDetails) {
         resultDisplay = {
           fileDiff: (originalDetails as ToolEditConfirmationDetails).fileDiff,
+          fileName: (originalDetails as ToolEditConfirmationDetails).fileName,
         };
       } else {
         resultDisplay = `~~${(originalDetails as ToolExecuteConfirmationDetails).command}~~`;
@@ -590,7 +591,7 @@ export const useGeminiStream = (
           addItem(
             {
               type: MessageType.ERROR,
-              text: `[Stream Error: ${getErrorMessage(error)}]`,
+              text: `[Stream Error: ${getErrorMessage(error) || 'Unknown error'}]`,
             },
             userMessageTimestamp,
           );

packages/server/package.json

@@ -12,6 +12,7 @@
     "format": "prettier --write .",
     "test": "vitest run",
     "test:ci": "vitest run --reporter=junit --outputFile=junit.xml",
+    "typecheck": "tsc --noEmit",
     "prerelease:version": "node ../../scripts/bind_package_version.js",
     "prerelease:deps": "node ../../scripts/bind_package_dependencies.js",
     "prepack": "npm run build"

packages/server/src/tools/edit.test.ts

@@ -0,0 +1,306 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/* eslint-disable @typescript-eslint/no-explicit-any */
+
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import { EditTool, EditToolParams } from './edit.js';
+import { FileDiff } from './tools.js';
+import path from 'path';
+import fs from 'fs';
+import os from 'os';
+import { Config } from '../config/config.js';
+
+// Mock GeminiClient
+const mockEnsureCorrectEdit = vi.fn();
+vi.mock('../core/client.js', () => ({
+  GeminiClient: vi.fn().mockImplementation(() => ({
+    // This is the method called by EditTool
+    ensureCorrectEdit: mockEnsureCorrectEdit,
+  })),
+}));
+
+describe('EditTool', () => {
+  let tool: EditTool;
+  let tempDir: string;
+  let rootDir: string;
+  let mockConfig: Config;
+
+  beforeEach(() => {
+    tempDir = fs.mkdtempSync(path.join(os.tmpdir(), 'edit-tool-test-'));
+    rootDir = path.join(tempDir, 'root');
+    fs.mkdirSync(rootDir);
+
+    mockConfig = {
+      getTargetDir: () => rootDir,
+      getGeminiConfig: () => ({ apiKey: 'test-api-key' }),
+      // Add other properties/methods of Config if EditTool uses them
+    } as unknown as Config;
+
+    // Reset mocks and set default implementation for ensureCorrectEdit
+    mockEnsureCorrectEdit.mockReset();
+    mockEnsureCorrectEdit.mockImplementation(async (currentContent, params) => {
+      let occurrences = 0;
+      if (params.old_string && currentContent) {
+        // Simple string counting for the mock
+        let index = currentContent.indexOf(params.old_string);
+        while (index !== -1) {
+          occurrences++;
+          index = currentContent.indexOf(params.old_string, index + 1);
+        }
+      } else if (params.old_string === '') {
+        occurrences = 0; // Creating a new file
+      }
+      return Promise.resolve({ params, occurrences });
+    });
+
+    tool = new EditTool(mockConfig); // GeminiClient is mocked via vi.mock
+  });
+
+  afterEach(() => {
+    fs.rmSync(tempDir, { recursive: true, force: true });
+    // vi.clearAllMocks(); // This might be too broad if other tests need persistent mocks
+  });
+
+  describe('validateParams', () => {
+    it('should return null for valid params', () => {
+      const params: EditToolParams = {
+        file_path: path.join(rootDir, 'test.txt'),
+        old_string: 'old',
+        new_string: 'new',
+      };
+      expect(tool.validateParams(params)).toBeNull();
+    });
+
+    it('should return error for relative path', () => {
+      const params: EditToolParams = {
+        file_path: 'test.txt',
+        old_string: 'old',
+        new_string: 'new',
+      };
+      expect(tool.validateParams(params)).toMatch(/File path must be absolute/);
+    });
+
+    it('should return error for path outside root', () => {
+      const params: EditToolParams = {
+        file_path: path.join(tempDir, 'outside-root.txt'),
+        old_string: 'old',
+        new_string: 'new',
+      };
+      expect(tool.validateParams(params)).toMatch(
+        /File path must be within the root directory/,
+      );
+    });
+  });
+
+  describe('shouldConfirmExecute', () => {
+    const testFile = 'edit_me.txt';
+    let filePath: string;
+
+    beforeEach(() => {
+      filePath = path.join(rootDir, testFile);
+    });
+
+    it('should return false if params are invalid', async () => {
+      const params: EditToolParams = {
+        file_path: 'relative.txt',
+        old_string: 'old',
+        new_string: 'new',
+      };
+      expect(await tool.shouldConfirmExecute(params)).toBe(false);
+    });
+
+    it('should request confirmation for valid edit', async () => {
+      fs.writeFileSync(filePath, 'some old content here');
+      const params: EditToolParams = {
+        file_path: filePath,
+        old_string: 'old',
+        new_string: 'new',
+      };
+      // ensureCorrectEdit will be called by shouldConfirmExecute
+      mockEnsureCorrectEdit.mockResolvedValueOnce({ params, occurrences: 1 });
+      const confirmation = await tool.shouldConfirmExecute(params);
+      expect(confirmation).toEqual(
+        expect.objectContaining({
+          title: `Confirm Edit: ${testFile}`,
+          fileName: testFile,
+          fileDiff: expect.any(String),
+        }),
+      );
+    });
+
+    it('should return false if old_string is not found (ensureCorrectEdit returns 0)', async () => {
+      fs.writeFileSync(filePath, 'some content here');
+      const params: EditToolParams = {
+        file_path: filePath,
+        old_string: 'not_found',
+        new_string: 'new',
+      };
+      mockEnsureCorrectEdit.mockResolvedValueOnce({ params, occurrences: 0 });
+      expect(await tool.shouldConfirmExecute(params)).toBe(false);
+    });
+
+    it('should return false if multiple occurrences of old_string are found (ensureCorrectEdit returns > 1)', async () => {
+      fs.writeFileSync(filePath, 'old old content here');
+      const params: EditToolParams = {
+        file_path: filePath,
+        old_string: 'old',
+        new_string: 'new',
+      };
+      mockEnsureCorrectEdit.mockResolvedValueOnce({ params, occurrences: 2 });
+      expect(await tool.shouldConfirmExecute(params)).toBe(false);
+    });
+
+    it('should request confirmation for creating a new file (empty old_string)', async () => {
+      const newFileName = 'new_file.txt';
+      const newFilePath = path.join(rootDir, newFileName);
+      const params: EditToolParams = {
+        file_path: newFilePath,
+        old_string: '',
+        new_string: 'new file content',
+      };
+      // ensureCorrectEdit might not be called if old_string is empty,
+      // as shouldConfirmExecute handles this for diff generation.
+      // If it is called, it should return 0 occurrences for a new file.
+      mockEnsureCorrectEdit.mockResolvedValueOnce({ params, occurrences: 0 });
+      const confirmation = await tool.shouldConfirmExecute(params);
+      expect(confirmation).toEqual(
+        expect.objectContaining({
+          title: `Confirm Edit: ${newFileName}`,
+          fileName: newFileName,
+          fileDiff: expect.any(String),
+        }),
+      );
+    });
+  });
+
+  describe('execute', () => {
+    const testFile = 'execute_me.txt';
+    let filePath: string;
+
+    beforeEach(() => {
+      filePath = path.join(rootDir, testFile);
+      // Default for execute tests, can be overridden
+      mockEnsureCorrectEdit.mockImplementation(async (content, params) => {
+        let occurrences = 0;
+        if (params.old_string && content) {
+          let index = content.indexOf(params.old_string);
+          while (index !== -1) {
+            occurrences++;
+            index = content.indexOf(params.old_string, index + 1);
+          }
+        } else if (params.old_string === '') {
+          occurrences = 0;
+        }
+        return { params, occurrences };
+      });
+    });
+
+    it('should return error if params are invalid', async () => {
+      const params: EditToolParams = {
+        file_path: 'relative.txt',
+        old_string: 'old',
+        new_string: 'new',
+      };
+      const result = await tool.execute(params, new AbortController().signal);
+      expect(result.llmContent).toMatch(/Error: Invalid parameters provided/);
+      expect(result.returnDisplay).toMatch(/Error: File path must be absolute/);
+    });
+
+    it('should edit an existing file and return diff with fileName', async () => {
+      const initialContent = 'This is some old text.';
+      const newContent = 'This is some new text.'; // old -> new
+      fs.writeFileSync(filePath, initialContent, 'utf8');
+      const params: EditToolParams = {
+        file_path: filePath,
+        old_string: 'old',
+        new_string: 'new',
+      };
+
+      // Specific mock for this test's execution path in calculateEdit
+      // ensureCorrectEdit is NOT called by calculateEdit, only by shouldConfirmExecute
+      // So, the default mockEnsureCorrectEdit should correctly return 1 occurrence for 'old' in initialContent
+
+      // Simulate confirmation by setting shouldAlwaysEdit
+      (tool as any).shouldAlwaysEdit = true;
+
+      const result = await tool.execute(params, new AbortController().signal);
+
+      (tool as any).shouldAlwaysEdit = false; // Reset for other tests
+
+      expect(result.llmContent).toMatch(/Successfully modified file/);
+      expect(fs.readFileSync(filePath, 'utf8')).toBe(newContent);
+      const display = result.returnDisplay as FileDiff;
+      expect(display.fileDiff).toMatch(initialContent);
+      expect(display.fileDiff).toMatch(newContent);
+      expect(display.fileName).toBe(testFile);
+    });
+
+    it('should create a new file if old_string is empty and file does not exist, and return created message', async () => {
+      const newFileName = 'brand_new_file.txt';
+      const newFilePath = path.join(rootDir, newFileName);
+      const fileContent = 'Content for the new file.';
+      const params: EditToolParams = {
+        file_path: newFilePath,
+        old_string: '',
+        new_string: fileContent,
+      };
+
+      (tool as any).shouldAlwaysEdit = true;
+      const result = await tool.execute(params, new AbortController().signal);
+      (tool as any).shouldAlwaysEdit = false;
+
+      expect(result.llmContent).toMatch(/Created new file/);
+      expect(fs.existsSync(newFilePath)).toBe(true);
+      expect(fs.readFileSync(newFilePath, 'utf8')).toBe(fileContent);
+      expect(result.returnDisplay).toBe(`Created ${newFileName}`);
+    });
+
+    it('should return error if old_string is not found in file', async () => {
+      fs.writeFileSync(filePath, 'Some content.', 'utf8');
+      const params: EditToolParams = {
+        file_path: filePath,
+        old_string: 'nonexistent',
+        new_string: 'replacement',
+      };
+      // The default mockEnsureCorrectEdit will return 0 occurrences for 'nonexistent'
+      const result = await tool.execute(params, new AbortController().signal);
+      expect(result.llmContent).toMatch(/0 occurrences found/);
+      expect(result.returnDisplay).toMatch(
+        /Failed to edit, could not find the string to replace/,
+      );
+    });
+
+    it('should return error if multiple occurrences of old_string are found', async () => {
+      fs.writeFileSync(filePath, 'multiple old old strings', 'utf8');
+      const params: EditToolParams = {
+        file_path: filePath,
+        old_string: 'old',
+        new_string: 'new',
+      };
+      // The default mockEnsureCorrectEdit will return 2 occurrences for 'old'
+      const result = await tool.execute(params, new AbortController().signal);
+      expect(result.llmContent).toMatch(/Expected 1 occurrences but found 2/);
+      expect(result.returnDisplay).toMatch(
+        /Failed to edit, expected 1 occurrence\(s\) but found 2/,
+      );
+    });
+
+    it('should return error if trying to create a file that already exists (empty old_string)', async () => {
+      fs.writeFileSync(filePath, 'Existing content', 'utf8');
+      const params: EditToolParams = {
+        file_path: filePath,
+        old_string: '',
+        new_string: 'new content',
+      };
+      const result = await tool.execute(params, new AbortController().signal);
+      expect(result.llmContent).toMatch(/File already exists, cannot create/);
+      expect(result.returnDisplay).toMatch(
+        /Attempted to create a file that already exists/,
+      );
+    });
+  });
+});

packages/server/src/tools/edit.ts

@@ -372,7 +372,7 @@ Expectation for parameters:
           'Proposed',
           { context: 3 },
         );
-        displayResult = { fileDiff };
+        displayResult = { fileDiff, fileName };
       }
 
       const llmSuccessMessage = editData.isNewFile

packages/server/src/tools/tools.ts

@@ -168,6 +168,7 @@ export type ToolResultDisplay = string | FileDiff;
 
 export interface FileDiff {
   fileDiff: string;
+  fileName: string;
 }
 
 export interface ToolCallConfirmationDetails {

packages/server/src/tools/write-file.test.ts

@@ -6,7 +6,7 @@
 
 import { describe, it, expect, beforeEach, afterEach } from 'vitest';
 import { WriteFileTool } from './write-file.js';
-import { ToolConfirmationOutcome } from './tools.js';
+import { FileDiff, ToolConfirmationOutcome } from './tools.js';
 import path from 'path';
 import fs from 'fs';
 import os from 'os';
@@ -152,7 +152,8 @@ describe('WriteFileTool', () => {
       );
       expect(fs.existsSync(filePath)).toBe(true);
       expect(fs.readFileSync(filePath, 'utf8')).toBe(content);
-      const display = result.returnDisplay as { fileDiff: string }; // Type assertion
+      const display = result.returnDisplay as FileDiff; // Type assertion
+      expect(display.fileName).toBe('execute_new_file.txt');
       // For new files, the diff will include the filename in the "Original" header
       expect(display.fileDiff).toMatch(/--- execute_new_file.txt\tOriginal/);
       expect(display.fileDiff).toMatch(/\+\+\+ execute_new_file.txt\tWritten/);
@@ -176,7 +177,8 @@ describe('WriteFileTool', () => {
 
       expect(result.llmContent).toMatch(/Successfully overwrote file/);
       expect(fs.readFileSync(filePath, 'utf8')).toBe(newContent);
-      const display = result.returnDisplay as { fileDiff: string }; // Type assertion
+      const display = result.returnDisplay as FileDiff; // Type assertion
+      expect(display.fileName).toBe('execute_existing_file.txt');
       expect(display.fileDiff).toMatch(initialContent);
       expect(display.fileDiff).toMatch(newContent);
     });

packages/server/src/tools/write-file.ts

@@ -202,7 +202,7 @@ export class WriteFileTool extends BaseTool<WriteFileToolParams, ToolResult> {
         ? `Successfully created and wrote to new file: ${params.file_path}`
         : `Successfully overwrote file: ${params.file_path}`;
 
-      const displayResult: FileDiff = { fileDiff };
+      const displayResult: FileDiff = { fileDiff, fileName };
 
       return {
         llmContent: llmSuccessMessage,