feat: implement file system reversion utilities for rewind (#15715)

packages/core/src/utils/fileDiffUtils.test.ts

@@ -0,0 +1,104 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect } from 'vitest';
+import {
+  getFileDiffFromResultDisplay,
+  computeAddedAndRemovedLines,
+} from './fileDiffUtils.js';
+import type { FileDiff, ToolResultDisplay } from '../tools/tools.js';
+
+describe('fileDiffUtils', () => {
+  describe('getFileDiffFromResultDisplay', () => {
+    it('returns undefined if resultDisplay is undefined', () => {
+      expect(getFileDiffFromResultDisplay(undefined)).toBeUndefined();
+    });
+
+    it('returns undefined if resultDisplay is not an object', () => {
+      expect(
+        getFileDiffFromResultDisplay('string' as ToolResultDisplay),
+      ).toBeUndefined();
+    });
+
+    it('returns undefined if resultDisplay missing diffStat', () => {
+      const resultDisplay = {
+        fileName: 'file.txt',
+      };
+      expect(
+        getFileDiffFromResultDisplay(resultDisplay as ToolResultDisplay),
+      ).toBeUndefined();
+    });
+
+    it('returns the FileDiff object if structure is valid', () => {
+      const validDiffStat = {
+        model_added_lines: 1,
+        model_removed_lines: 2,
+        user_added_lines: 3,
+        user_removed_lines: 4,
+        model_added_chars: 10,
+        model_removed_chars: 20,
+        user_added_chars: 30,
+        user_removed_chars: 40,
+      };
+      const resultDisplay = {
+        fileName: 'file.txt',
+        diffStat: validDiffStat,
+      };
+
+      const result = getFileDiffFromResultDisplay(
+        resultDisplay as ToolResultDisplay,
+      );
+      expect(result).toBe(resultDisplay);
+    });
+  });
+
+  describe('computeAddedAndRemovedLines', () => {
+    it('returns 0 added and 0 removed if stats is undefined', () => {
+      expect(computeAddedAndRemovedLines(undefined)).toEqual({
+        addedLines: 0,
+        removedLines: 0,
+      });
+    });
+
+    it('correctly sums added and removed lines from stats', () => {
+      const stats: FileDiff['diffStat'] = {
+        model_added_lines: 10,
+        model_removed_lines: 5,
+        user_added_lines: 2,
+        user_removed_lines: 1,
+        model_added_chars: 100,
+        model_removed_chars: 50,
+        user_added_chars: 20,
+        user_removed_chars: 10,
+      };
+
+      const result = computeAddedAndRemovedLines(stats);
+      expect(result).toEqual({
+        addedLines: 12, // 10 + 2
+        removedLines: 6, // 5 + 1
+      });
+    });
+
+    it('handles zero values correctly', () => {
+      const stats: FileDiff['diffStat'] = {
+        model_added_lines: 0,
+        model_removed_lines: 0,
+        user_added_lines: 0,
+        user_removed_lines: 0,
+        model_added_chars: 0,
+        model_removed_chars: 0,
+        user_added_chars: 0,
+        user_removed_chars: 0,
+      };
+
+      const result = computeAddedAndRemovedLines(stats);
+      expect(result).toEqual({
+        addedLines: 0,
+        removedLines: 0,
+      });
+    });
+  });
+});

packages/core/src/utils/fileDiffUtils.ts

@@ -0,0 +1,50 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import type { FileDiff } from '../tools/tools.js';
+import type { ToolCallRecord } from '../services/chatRecordingService.js';
+
+/**
+ * Safely extracts the FileDiff object from a tool call's resultDisplay.
+ * This helper performs runtime checks to ensure the object conforms to the FileDiff structure.
+ * @param resultDisplay The resultDisplay property of a ToolCallRecord.
+ * @returns The FileDiff object if found and valid, otherwise undefined.
+ */
+export function getFileDiffFromResultDisplay(
+  resultDisplay: ToolCallRecord['resultDisplay'],
+): FileDiff | undefined {
+  if (
+    resultDisplay &&
+    typeof resultDisplay === 'object' &&
+    'diffStat' in resultDisplay &&
+    typeof resultDisplay.diffStat === 'object' &&
+    resultDisplay.diffStat !== null
+  ) {
+    const diffStat = resultDisplay.diffStat as FileDiff['diffStat'];
+    if (diffStat) {
+      return resultDisplay;
+    }
+  }
+  return undefined;
+}
+
+export function computeAddedAndRemovedLines(
+  stats: FileDiff['diffStat'] | undefined,
+): {
+  addedLines: number;
+  removedLines: number;
+} {
+  if (!stats) {
+    return {
+      addedLines: 0,
+      removedLines: 0,
+    };
+  }
+  return {
+    addedLines: stats.model_added_lines + stats.user_added_lines,
+    removedLines: stats.model_removed_lines + stats.user_removed_lines,
+  };
+}