fix: remove trailing newline added by markdown-it (#585)

Co-authored-by: Anthony Fu <anthonyfu117@hotmail.com>

packages/markdown-it/src/core.ts

@@ -11,6 +11,16 @@ export interface MarkdownItShikiExtraOptions {
     code: string,
     lang: string,
   ) => Record<string, any> | undefined | null
+
+  /**
+   * markdown-it's highlight function will add a trailing newline to the code.
+   *
+   * This integration removes the trailing newline to the code by default,
+   * you can turn this off by passing false.
+   *
+   * @default true
+   */
+  trimEndingNewline?: boolean
 }
 
 export type MarkdownItShikiSetupOptions =
@@ -26,6 +36,7 @@ export function setupMarkdownIt(
 ) {
   const {
     parseMetaString,
+    trimEndingNewline = true,
   } = options
 
   markdownit.options.highlight = (code, lang = 'text', attrs) => {
@@ -49,6 +60,11 @@ export function setupMarkdownIt(
       },
     })
 
+    if (trimEndingNewline) {
+      if (code.endsWith('\n'))
+        code = code.slice(0, -1)
+    }
+
     return highlighter.codeToHtml(
       code,
       {