feat(rehype): trim trailing new line passed in from rehype/remark (#729)

Co-authored-by: Anthony Fu <github@antfu.me>

Author: Ovyerus

packages/rehype/src/core.ts

@@ -28,6 +28,16 @@ export interface RehypeShikiExtraOptions {
    */
   fallbackLanguage?: string
 
+  /**
+   * `mdast-util-to-hast` adds a newline to the end of code blocks
+   *
+   * This option strips that newline from the code block
+   *
+   * @default true
+   * @see https://github.com/syntax-tree/mdast-util-to-hast/blob/f511a93817b131fb73419bf7d24d73a5b8b0f0c2/lib/handlers/code.js#L22
+   */
+  stripEndNewline?: boolean
+
   /**
    * Custom meta string parser
    * Return an object to merge with `meta`
@@ -73,6 +83,7 @@ function rehypeShikiFromHighlighter(
     defaultLanguage,
     fallbackLanguage,
     onError,
+    stripEndNewline = true,
     ...rest
   } = options
 
@@ -107,7 +118,11 @@ function rehypeShikiFromHighlighter(
       if (fallbackLanguage && !langs.includes(lang))
         lang = fallbackLanguage
 
-      const code = toString(head)
+      let code = toString(head)
+
+      if (stripEndNewline && code.endsWith('\n'))
+        code = code.slice(0, -1)
+
       const cachedValue = cache?.get(code)
 
       if (cachedValue) {

packages/rehype/test/fixtures/a.core.out.html

@@ -63,3 +63,18 @@ it('add-custom-cache', async () => {
 
   expect(file.toString()).toMatchFileSnapshot('./fixtures/c.out.html')
 })
+
+it('does not add extra trailing blank line', async () => {
+  const file = await unified()
+    .use(remarkParse)
+    .use(remarkRehype)
+    .use(rehypeShiki, {
+      theme: 'vitesse-light',
+      defaultLanguage: 'text',
+    })
+    .use(rehypeStringify)
+    .process('```\nthis should only have one .line\n```')
+
+  const lineCount = file.toString().match(/class="line"/g)?.length ?? 0
+  expect(lineCount).toEqual(1)
+})