⚡ perf(vscode): 代码阅读预览发给页面的块只记相对位置：块在源码里占的地方记成离前一块多远、自己多长，块里名字的下标从块的开头算，页面从文件开头累加回文件里的位置、和扩展端打交道的地方都在一处换算；靠前改了代码，后面内容没变的块发过去一模一样，扩展端自己的块和发给页面的块分成两种类型

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

@@ -0,0 +1,84 @@
+import type { BlockView as HostBlockView } from '../../../src/codeReader/blockView'
+import type { BlockView } from './types'
+import { describe, expect, it } from 'vitest'
+import { toBlockViews } from '../../../src/codeReader/blockView'
+import { pageBlocks } from '../../../src/codeReader/editor/pageBlocks'
+import { createPythonAdapter } from '../../../src/codeReader/languages/python'
+import { WASM_DIR, withBlocks } from '../../../src/codeReader/testSupport'
+import { pythonZhTranslator } from '../../../src/codeReader/translators/pythonZh'
+import { placementOf } from './placement'
+
+const py = createPythonAdapter(WASM_DIR)
+
+async function views(source: string): Promise<HostBlockView[]> {
+  return withBlocks(py, 'python', source, blocks => toBlockViews(blocks, { source, language: py, markers: [] }, pythonZhTranslator))
+}
+
+function flatten<T extends { children: T[] }>(list: T[]): T[] {
+  return list.flatMap(block => [block, ...flatten(block.children)])
+}
+
+function byId(blocks: BlockView[]): Map<string, BlockView> {
+  return new Map(flatten(blocks).map(block => [block.id, block]))
+}
+
+/** 一块自己的样子（不连子块）：子块变了不算它变了 */
+function own({ children: _, ...rest }: BlockView): Omit<BlockView, 'children'> {
+  return rest
+}
+
+const SOURCE = [
+  'import os',
+  '',
+  'def helper(value):',
+  '    return value + 1',
+  '',
+  'class Store:',
+  '    def load(self, key):',
+  '        if key:',
+  '            return os.getenv(key)',
+  '        return None',
+  '',
+  'LIMIT = 3',
+].join('\n')
+
+describe('块在文件里的位置：扩展端记成相对的，页面累加回来', () => {
+  it('每块累加出来的首行、尾行、开头的下标同扩展端的一样；块里的下标加上块的开头就是文件里的', async () => {
+    const host = await views(SOURCE)
+    const placement = placementOf(pageBlocks(host, SOURCE))
+    const lineStarts = SOURCE.split('\n').map((_, line, lines) => lines.slice(0, line).join('\n').length + (line > 0 ? 1 : 0))
+    for (const block of flatten(host)) {
+      expect(placement.of(block.id), block.id).toEqual({ offset: lineStarts[block.startLine], line: block.startLine, endLine: block.endLine })
+    }
+    const page = byId(pageBlocks(host, SOURCE))
+    for (const block of flatten(host).filter(block => block.defines)) {
+      const base = placement.of(block.id)!.offset
+      const defines = page.get(block.id)!.defines!
+      expect(SOURCE.slice(base + defines.startIndex, base + defines.endIndex), block.id).toBe(SOURCE.slice(block.defines!.startIndex, block.defines!.endIndex))
+    }
+  })
+
+  it('靠前的一块里改了一个字：只有那块变了，包着它的块只是长了一个字，后面的块发出去一模一样', async () => {
+    const edited = SOURCE.replace('value + 1', 'value + 10')
+    const before = byId(pageBlocks(await views(SOURCE), SOURCE))
+    const after = byId(pageBlocks(await views(edited), edited))
+    const changed = [...after.keys()].filter(id => JSON.stringify(own(after.get(id)!)) !== JSON.stringify(own(before.get(id)!)))
+    expect(changed).toEqual(['1', '1.0'])
+    expect(own(after.get('1')!)).toEqual({ ...own(before.get('1')!), span: { ...before.get('1')!.span, length: before.get('1')!.span.length + 1 } })
+  })
+
+  it('上面多了几行：只有紧跟在后面的那块离前一块远了，其余块发出去一模一样，累加出来的位置都往后挪', async () => {
+    const shifted = SOURCE.replace('import os\n', 'import os\n\n\n')
+    const old = pageBlocks(await views(SOURCE), SOURCE)
+    const page = pageBlocks(await views(shifted), shifted)
+    const before = byId(old)
+    const after = byId(page)
+    const changed = [...after.keys()].filter(id => JSON.stringify(own(after.get(id)!)) !== JSON.stringify(own(before.get(id)!)))
+    expect(changed).toEqual(['1'])
+    expect(after.get('1')!.span).toEqual({ ...before.get('1')!.span, lineGap: before.get('1')!.span.lineGap + 2, gap: before.get('1')!.span.gap + 2 })
+    for (const id of [...after.keys()].filter(id => id !== '0')) {
+      const was = placementOf(old).of(id)!
+      expect(placementOf(page).of(id), id).toEqual({ offset: was.offset + 2, line: was.line + 2, endLine: was.endLine + 2 })
+    }
+  })
+})