feat(markdown-it): support default and fallback lang #687 (#689)

Co-authored-by: winnliu <@waw981109@>

Author: Only566

packages/markdown-it/src/core.ts

@@ -1,5 +1,15 @@
 import type MarkdownIt from 'markdown-it'
-import type { BuiltinTheme, CodeOptionsMeta, CodeOptionsThemes, CodeToHastOptions, HighlighterGeneric, ShikiTransformer, TransformerOptions } from 'shiki'
+import type {
+  BuiltinLanguage,
+  BuiltinTheme,
+  CodeOptionsMeta,
+  CodeOptionsThemes,
+  CodeToHastOptions,
+  HighlighterGeneric,
+  LanguageInput,
+  ShikiTransformer,
+  TransformerOptions,
+} from 'shiki'
 
 export interface MarkdownItShikiExtraOptions {
   /**
@@ -21,6 +31,18 @@ export interface MarkdownItShikiExtraOptions {
    * @default true
    */
   trimEndingNewline?: boolean
+
+  /**
+   * When lang of code block is empty string, it will work.
+   *
+   * @default 'text'
+   */
+  defaultLanguage?: LanguageInput | BuiltinLanguage
+
+  /**
+   * When lang of code block is not included in langs of options, it will be as a fallback lang.
+   */
+  fallbackLanguage?: LanguageInput | BuiltinLanguage
 }
 
 export type MarkdownItShikiSetupOptions =
@@ -37,9 +59,17 @@ export function setupMarkdownIt(
   const {
     parseMetaString,
     trimEndingNewline = true,
+    defaultLanguage = 'text',
+    fallbackLanguage,
   } = options
-
+  const langs = highlighter.getLoadedLanguages()
   markdownit.options.highlight = (code, lang = 'text', attrs) => {
+    if (lang === '') {
+      lang = defaultLanguage as string
+    }
+    if (fallbackLanguage && !langs.includes(lang)) {
+      lang = fallbackLanguage as string
+    }
     const meta = parseMetaString?.(attrs, code, lang) || {}
     const codeOptions: CodeToHastOptions = {
       ...options,

packages/markdown-it/test/fixtures/b.md

@@ -4,7 +4,7 @@ import MarkdownIt from 'markdown-it'
 import { transformerMetaHighlight } from '@shikijs/transformers'
 import Shiki from '../src'
 
-it('run', async () => {
+it('run for base', async () => {
   const md = MarkdownIt()
   md.use(await Shiki({
     themes: {
@@ -20,3 +20,37 @@ it('run', async () => {
 
   expect(result).toMatchFileSnapshot('./fixtures/a.out.html')
 })
+it('run for fallback language', async () => {
+  const md = MarkdownIt()
+  md.use(await Shiki({
+    themes: {
+      light: 'vitesse-light',
+      dark: 'vitesse-dark',
+    },
+    fallbackLanguage: 'js',
+    transformers: [
+      transformerMetaHighlight(),
+    ],
+  }))
+
+  const result = md.render(await fs.readFile(new URL('./fixtures/b.md', import.meta.url), 'utf-8'))
+
+  expect(result).toMatchFileSnapshot('./fixtures/b.out.html')
+})
+it('run for default language', async () => {
+  const md = MarkdownIt()
+  md.use(await Shiki({
+    themes: {
+      light: 'vitesse-light',
+      dark: 'vitesse-dark',
+    },
+    defaultLanguage: 'js',
+    transformers: [
+      transformerMetaHighlight(),
+    ],
+  }))
+
+  const result = md.render(await fs.readFile(new URL('./fixtures/c.md', import.meta.url), 'utf-8'))
+
+  expect(result).toMatchFileSnapshot('./fixtures/c.out.html')
+})