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

1 files changed, 5 insertions, 3 deletions

diff --git a/packages/server/src/tools/write-file.test.ts b/packages/server/src/tools/write-file.test.ts
index 2ce5cdf5..25d1e998 100644
--- a/packages/server/src/tools/write-file.test.ts
+++ b/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);
     });