⚡ perf(vscode): 代码阅读预览发给页面的块带内容指纹：扩展端按卡片内容、在源码里占的地方连同子块的指纹算摘要，页面按指纹认出没变的块沿用原来的对象，不再逐块深比内容，5126 行的文档到了比对 10.6ms → 0.4ms

vscode/webview-ui/src/codeReader/sharing.test.ts

@@ -1,5 +1,43 @@
+import type { UnhashedBlock } from './testBlocks'
 import { describe, expect, it } from 'vitest'
-import { shareUnchanged } from './sharing'
+import { shareBlocks, shareUnchanged } from './sharing'
+import { hashed, NO_SPAN } from './testBlocks'
+
+describe('新文档里指纹没变的块沿用上一份的对象', () => {
+  function card(id: string, text: string, children: UnhashedBlock[] = []): UnhashedBlock {
+    return { id, anchor: id, kind: 'statement', span: NO_SPAN, attributes: {}, concepts: [], children, translation: [{ text, role: 'plain' }] }
+  }
+  const PREV = hashed([card('0', 'a'), card('1', 'b', [card('1.0', 'c'), card('1.1', 'd')]), card('2', 'e')])
+
+  it('整份一样：交回上一份本身；没有上一份时原样交回', () => {
+    const same = hashed([card('0', 'a'), card('1', 'b', [card('1.0', 'c'), card('1.1', 'd')]), card('2', 'e')])
+    expect(shareBlocks(PREV, same)).toBe(PREV)
+    expect(shareBlocks(undefined, same)).toBe(same)
+  })
+
+  it('子块改了：它和包着它的块是新的，别的块（连同改了的块旁边没变的子块）还是原来的对象', () => {
+    const next = hashed([card('0', 'a'), card('1', 'b', [card('1.0', 'c'), card('1.1', 'D')]), card('2', 'e')])
+    const shared = shareBlocks(PREV, next)
+    expect(shared).toEqual(next)
+    expect(shared).not.toBe(PREV)
+    expect(shared[0]).toBe(PREV[0])
+    expect(shared[2]).toBe(PREV[2])
+    expect(shared[1]).not.toBe(PREV[1])
+    expect(shared[1].children[0]).toBe(PREV[1].children[0])
+    expect(shared[1].children[1]).not.toBe(PREV[1].children[1])
+  })
+
+  it('多了、少了块：那一层是新的数组，没变的块照样沿用', () => {
+    const longer = shareBlocks(PREV, hashed([card('0', 'a'), card('1', 'b', [card('1.0', 'c'), card('1.1', 'd')]), card('2', 'e'), card('3', 'f')]))
+    expect(longer).not.toBe(PREV)
+    expect(longer.slice(0, 3)).toEqual(PREV)
+    longer.slice(0, 3).forEach((block, index) => expect(block).toBe(PREV[index]))
+    const shorter = shareBlocks(PREV, hashed([card('0', 'a'), card('1', 'b', [card('1.0', 'c')]), card('2', 'e')]))
+    expect(shorter[1]).not.toBe(PREV[1])
+    expect(shorter[1].children[0]).toBe(PREV[1].children[0])
+    expect(shorter[2]).toBe(PREV[2])
+  })
+})
 
 describe('新消息里没变的部分沿用上一份的对象', () => {
   const prev = {