fix(build): remove frontmatter in md file inclusion

closes #3195

Author: brc-dd

__tests__/e2e/markdown-extensions/markdown-extensions.test.ts

@@ -274,4 +274,9 @@ describe('Markdown File Inclusion', () => {
     expect(trim(await p.nth(0).textContent())).toBe('This is a region')
     expect(trim(await p.nth(1).textContent())).toBe('This is after region')
   })
+
+  test('ignore frontmatter if range is not specified', async () => {
+    const p = page.locator('.vp-doc')
+    expect(await p.textContent()).not.toContain('title')
+  })
 })

__tests__/e2e/markdown-extensions/nested-include.md

@@ -1,3 +1,7 @@
+---
+title: Nested Include
+---
+
 <!--@include: ./foo.md-->
 
 ### After Foo

src/node/utils/processIncludes.ts

@@ -1,5 +1,6 @@
-import path from 'path'
 import fs from 'fs-extra'
+import matter from 'gray-matter'
+import path from 'path'
 import { slash } from '../shared'
 
 export function processIncludes(
@@ -30,6 +31,8 @@ export function processIncludes(
             endLine ? parseInt(endLine, 10) : undefined
           )
           .join('\n')
+      } else {
+        content = matter(content).content
       }
       includes.push(slash(includePath))
       // recursively process includes in the content