fixing lines overlapping

test/diff-view.test.ts

@@ -0,0 +1,45 @@
+import { describe, it, expect } from 'vitest'
+import { buildDiffView } from '../src/renderer/src/editor'
+import { makeDiff } from '../src/renderer/src/diff'
+
+/** The current-side view of one text pair, plus the map the overlay reads. */
+function view(original: string, updated: string): ReturnType<typeof buildDiffView> {
+  return buildDiffView(makeDiff('M', original, updated))
+}
+
+describe('buildDiffView', () => {
+  it('maps an added line to the line it replaced', () => {
+    const { lines, peek } = view('a\nold\nb', 'a\nnew\nb')
+    expect(lines.map((l) => l.text)).toEqual(['a', 'new', 'b'])
+    expect(lines[1].row).toBe('add')
+    expect(peek.get(2)).toEqual({ anchor: 2, from: 2, to: 2 })
+    expect(lines.every((l) => !l.gap)).toBe(true)
+  })
+
+  it('puts a pure deletion on the line that follows it', () => {
+    const { lines, peek } = view('a\ngone\nb', 'a\nb')
+    expect(lines[1].text).toBe('b')
+    expect(lines[1].gap).toBe('above')
+    expect(lines[1].row).toBeNull()
+    expect(peek.get(2)).toEqual({ anchor: 2, from: 2, to: 2 })
+  })
+
+  it('puts a deletion at end of file under the last line', () => {
+    const { lines, peek } = view('a\nb\ntail', 'a\nb')
+    expect(lines[1].gap).toBe('below')
+    expect(peek.get(2)).toEqual({ anchor: 3, from: 3, to: 3 })
+  })
+
+  it('anchors an insertion but marks nothing as removed', () => {
+    const { lines, peek } = view('a\nb', 'a\nNEW\nb')
+    expect(lines[1].row).toBe('add')
+    expect(peek.get(2)).toEqual({ anchor: 1, from: null, to: null })
+    expect(lines.every((l) => !l.gap)).toBe(true)
+  })
+
+  it('leaves an unchanged file without marks or peek targets', () => {
+    const { lines, peek } = view('a\nb\n', 'a\nb\n')
+    expect(peek.size).toBe(0)
+    expect(lines.every((l) => !l.row && !l.gap)).toBe(true)
+  })
+})