feat(core): warning on too many instances, close #693

Author: antfu

docs/guide/install.md

@@ -102,6 +102,12 @@ const code = highlighter.codeToHtml('const a = 1', {
 })
 ```
 
+:::info Important Note
+Highlighter instance should be **long-lived singleton**. You might need to cache it somewhere and reuse it across your application. Avoid calling `getHighlighter` in hot functions or loops.
+
+If running on Node.js, we recommend using the [Shorthands](#shorthands) which manages the highlighter instance and dynamic theme/language loading for you.
+:::
+
 Additionally, if you want to load themes and languages after the highlighter is created, you can use the `loadTheme` and `loadLanguage` methods.
 
 ```ts twoslash

packages/core/src/internal.ts

@@ -16,10 +16,16 @@ export function setDefaultWasmLoader(_loader: LoadWasmOptions) {
   _defaultWasmLoader = _loader
 }
 
+let instancesCount = 0
+
 /**
  * Get the minimal shiki context for rendering.
  */
 export async function getShikiInternal(options: HighlighterCoreOptions = {}): Promise<ShikiInternal> {
+  instancesCount += 1
+  if (options.warnings !== false && instancesCount >= 10 && instancesCount % 10 === 0)
+    console.warn(`[Shiki] ${instancesCount} instances have been created. Shiki is supposed to be used as a singleton, consider refactoring your code to cache your highlighter instance.`)
+
   async function normalizeGetter<T>(p: MaybeGetter<T>): Promise<T> {
     return Promise.resolve(typeof p === 'function' ? (p as any)() : p).then(r => r.default || r)
   }

packages/core/src/types/options.ts

@@ -24,6 +24,11 @@ export interface HighlighterCoreOptions {
    * Load wasm file from a custom path or using a custom function.
    */
   loadWasm?: LoadWasmOptions
+  /**
+   * Emit console warnings to alert users of potential issues.
+   * @default true
+   */
+  warnings?: boolean
 }
 
 export interface BundledHighlighterOptions<L extends string, T extends string> {