Using transformerRenderWhitespace together with the structure "inline" option throws an error

[marpe]

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Describe the bug

Hi,

When using transformerRenderWhitespace together with the structure: "inline" setting I receive this error:

TypeError: Cannot read properties of undefined (reading 'forEach')
    at Object.root (http://localhost:3000/node_modules/.vite/deps/@shikijs_transformers.js?v=82b8e6ae:538:21)
    at tokensToHast (http://localhost:3000/node_modules/.vite/deps/chunk-EBWDM6ZB.js?v=82b8e6ae:1315:92)
    at codeToHast (http://localhost:3000/node_modules/.vite/deps/chunk-EBWDM6ZB.js?v=82b8e6ae:1188:10)
    at codeToHtml (http://localhost:3000/node_modules/.vite/deps/chunk-EBWDM6ZB.js?v=82b8e6ae:1400:27)
    at Object.codeToHtml (http://localhost:3000/node_modules/.vite/deps/chunk-EBWDM6ZB.js?v=82b8e6ae:1842:37)
    at Proxy.highlightCode (http://localhost:3000/lib/markdownHelpers.ts:89:22)
    at Proxy._sfc_render (http://localhost:3000/components/CodeBlock.vue:37:23)
    at renderComponentRoot (http://localhost:3000/node_modules/.vite/deps/chunk-IWYC5R2O.js?v=82b8e6ae:8581:17)
    at ReactiveEffect.componentUpdateFn [as fn] (http://localhost:3000/node_modules/.vite/deps/chunk-IWYC5R2O.js?v=82b8e6ae:7403:46)
    at ReactiveEffect.run (http://localhost:3000/node_modules/.vite/deps/chunk-IWYC5R2O.js?v=82b8e6ae:481:19)

Here is my test setup:

const code = `
  const foo = 'bar'
  console.log(foo)
  `;

appEl.innerHTML = await codeToHtml(code, {
  lang: 'js',
  theme: 'nord',
  structure: "inline", // try removing this
  transformers: [
    transformerRenderWhitespace(),
  ],
});

Packages:

{
  "name": "shiki-bug2",
  "private": true,
  "version": "0.0.0",
  "type": "module",
  "scripts": {
    "dev": "vite",
    "build": "tsc && vite build",
    "preview": "vite preview"
  },
  "devDependencies": {
    "typescript": "~5.7.2",
    "vite": "^6.2.0"
  },
  "dependencies": {
    "@shikijs/transformers": "^3.1.0",
    "shiki": "^3.1.0"
  }
}

Repro over here

Reproduction

https://stackblitz.com/~/github.com/marpe/shiki-structure-whitespace-bug

Contributes

• I am willing to submit a PR to fix this issue
• I am willing to submit a PR with failing tests

[nvlang]

I believe the issue lies here:

shiki/packages/transformers/src/transformers/render-whitespace.ts

Lines 45 to 47 in ac6bea5

	const pre = root.children[0] as Element
	const code = pre.children[0] as Element
	code.children.forEach((line) => {

Since, for structure: 'inline' the output isn't wrapped in either <pre> nor <code> tags, this will error.

I'm going to try to submit a fix.