feat(compare): implement Document Compare dialog with local-diff and git-HEAD-diff modes

Amit Haridas
2026-08-24 07:20:16 +05:30 · 2026-08-23 19:31:33 +05:30
parent 1f5db511ba
commit 758dcb4166
10 changed files with 769 additions and 3 deletions
@@ -0,0 +1,88 @@
+/**
+ * Tests for the LCS line diff used by the Document Compare dialog
+ * Covers: identical texts, pure additions, pure deletions, mixed edits, empty sides
+ */
+
+const { computeLineDiff } = require('../src/utils/line-diff');
+
+describe('computeLineDiff', () => {
+  it('reports every line as unchanged for identical texts', () => {
+    const text = '# Title\n\nSome paragraph.\n- item 1\n- item 2';
+    const result = computeLineDiff(text, text);
+    expect(result).toHaveLength(5);
+    expect(result.every((entry) => entry.type === 'unchanged')).toBe(true);
+    expect(result.map((entry) => entry.text)).toEqual([
+      '# Title',
+      '',
+      'Some paragraph.',
+      '- item 1',
+      '- item 2',
+    ]);
+  });
+
+  it('reports only additions when lines were appended', () => {
+    const result = computeLineDiff('# Title\n\nBody.', '# Title\n\nBody.\nNew line.\nAnother.');
+    expect(result.filter((entry) => entry.type === 'removed')).toEqual([]);
+    expect(result).toEqual([
+      { type: 'unchanged', text: '# Title' },
+      { type: 'unchanged', text: '' },
+      { type: 'unchanged', text: 'Body.' },
+      { type: 'added', text: 'New line.' },
+      { type: 'added', text: 'Another.' },
+    ]);
+  });
+
+  it('reports only removals when lines were deleted', () => {
+    const result = computeLineDiff('Intro\nKeep me\nDrop me\nAlso drop', 'Intro\nKeep me');
+    expect(result.filter((entry) => entry.type === 'added')).toEqual([]);
+    expect(result).toEqual([
+      { type: 'unchanged', text: 'Intro' },
+      { type: 'unchanged', text: 'Keep me' },
+      { type: 'removed', text: 'Drop me' },
+      { type: 'removed', text: 'Also drop' },
+    ]);
+  });
+
+  it('reports adjacent removed-then-added entries for a mixed change', () => {
+    const result = computeLineDiff(
+      '# Heading\nold paragraph\ntrailer',
+      '# Heading\nnew paragraph\ntrailer'
+    );
+    expect(result).toEqual([
+      { type: 'unchanged', text: '# Heading' },
+      { type: 'removed', text: 'old paragraph' },
+      { type: 'added', text: 'new paragraph' },
+      { type: 'unchanged', text: 'trailer' },
+    ]);
+  });
+
+  it('treats an empty old text as a pure addition', () => {
+    expect(computeLineDiff('', 'a\nb')).toEqual([
+      { type: 'added', text: 'a' },
+      { type: 'added', text: 'b' },
+    ]);
+  });
+
+  it('treats an empty new text as a pure removal', () => {
+    expect(computeLineDiff('a\nb', '')).toEqual([
+      { type: 'removed', text: 'a' },
+      { type: 'removed', text: 'b' },
+    ]);
+  });
+
+  it('ignores carriage-return differences between the two texts', () => {
+    const result = computeLineDiff('one\r\ntwo\r\n', 'one\ntwo\n');
+    expect(result).toEqual([
+      { type: 'unchanged', text: 'one' },
+      { type: 'unchanged', text: 'two' },
+    ]);
+  });
+
+  it('ignores a purely trailing-newline difference', () => {
+    const result = computeLineDiff('a\nb\n', 'a\nb');
+    expect(result).toEqual([
+      { type: 'unchanged', text: 'a' },
+      { type: 'unchanged', text: 'b' },
+    ]);
+  });
+});