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fix shiki perf issue (#2870)

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Fred K. Schott 2022-03-24 09:49:54 -07:00 committed by GitHub
parent 098f6f6b06
commit d763ec183e
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2 changed files with 16 additions and 5 deletions
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5
.changeset/silly-sloths-hammer.md Normal file
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@ -0,0 +1,5 @@
---
'@astrojs/markdown-remark': patch
---
Fix a shiki performance issue affecting large sites

16
packages/markdown/remark/src/remark-shiki.ts
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@ -33,19 +33,25 @@ export interface ShikiConfig {
/**
* getHighlighter() is the most expensive step of Shiki. Instead of calling it on every page,
* cache it here as much as possible. Make sure that your highlighters can be cached, state-free.
* We make this async, so that multiple calls to parse markdown still share the same highlighter.
*/
const highlighterCache = new Map<string, shiki.Highlighter>();
const highlighterCacheAsync = new Map<string, Promise<shiki.Highlighter>>();
const remarkShiki = async ({ langs = [], theme = 'github-dark', wrap = false }: ShikiConfig, scopedClassName?: string | null) => {
const cacheID: string = typeof theme === 'string' ? theme : theme.name;
let highlighter = highlighterCache.get(cacheID);
if (!highlighter) {
highlighter = await getHighlighter({ theme });
highlighterCache.set(cacheID, highlighter);
let highlighterAsync = highlighterCacheAsync.get(cacheID);
if (!highlighterAsync) {
highlighterAsync = getHighlighter({ theme });
highlighterCacheAsync.set(cacheID, highlighterAsync);
}
const highlighter = await highlighterAsync;
// NOTE: There may be a performance issue here for large sites that use `lang`.
// Since this will be called on every page load. Unclear how to fix this.
for (const lang of langs) {
await highlighter.loadLanguage(lang);
}
return () => (tree: any) => {
visit(tree, 'code', (node) => {
let html = highlighter!.codeToHtml(node.value, { lang: node.lang ?? 'plaintext' });