feat(build): support relative path for code snippet (#1894)

Co-authored-by: Divyansh Singh <40380293+brc-dd@users.noreply.github.com>

docs/guide/markdown.md

@@ -566,7 +566,12 @@ It also supports [line highlighting](#line-highlighting-in-code-blocks):
 <<< @/snippets/snippet.js{2}
 
 ::: tip
-The value of `@` corresponds to the source root. By default it's the VitePress project root, unless `srcDir` is configured.
+The value of `@` corresponds to the source root. By default it's the VitePress project root, unless `srcDir` is configured. Alternatively, you can also import from relative paths:
+
+```md
+<<< ../snippets/snippet.js
+```
+
 :::
 
 You can also use a [VS Code region](https://code.visualstudio.com/docs/editor/codebasics#_folding) to only include the corresponding part of the code file. You can provide a custom region name after a `#` following the filepath:

src/node/markdown/plugins/snippet.ts

@@ -2,6 +2,7 @@ import fs from 'fs-extra'
 import path from 'path'
 import type MarkdownIt from 'markdown-it'
 import type { RuleBlock } from 'markdown-it/lib/parser_block'
+import type { MarkdownEnv } from '../env'
 
 export function dedent(text: string): string {
   const lines = text.split('\n')
@@ -107,7 +108,7 @@ export const snippetPlugin = (md: MarkdownIt, srcDir: string) => {
       .trim()
 
     const [
-      filename = '',
+      filepath = '',
       extension = '',
       region = '',
       lines = '',
@@ -115,7 +116,7 @@ export const snippetPlugin = (md: MarkdownIt, srcDir: string) => {
       rawTitle = ''
     ] = (rawPathRegexp.exec(rawPath) || []).slice(1)
 
-    const title = rawTitle || filename.split('/').pop() || ''
+    const title = rawTitle || filepath.split('/').pop() || ''
 
     state.line = startLine + 1
 
@@ -124,8 +125,12 @@ export const snippetPlugin = (md: MarkdownIt, srcDir: string) => {
       title ? `[${title}]` : ''
     }`
 
+    const resolvedPath = path.resolve(
+      path.dirname((state.env as MarkdownEnv).path),
+      filepath
+    )
     // @ts-ignore
-    token.src = path.resolve(filename) + region
+    token.src = [resolvedPath, region.slice(1)]
     token.markup = '```'
     token.map = [startLine, startLine + 1]
 
@@ -138,8 +143,7 @@ export const snippetPlugin = (md: MarkdownIt, srcDir: string) => {
     const [tokens, idx, , { loader }] = args
     const token = tokens[idx]
     // @ts-ignore
-    const tokenSrc = token.src
-    const [src, regionName] = tokenSrc ? tokenSrc.split('#') : ['']
+    const [src, regionName] = token.src ?? []
 
     if (src) {
       if (loader) {