feat: add support to import files as code fence (#538)

docs/guide/markdown.md

@@ -224,6 +224,18 @@ export default {
 }
 ```
 
+## Import Code Snippets
+
+**Input**
+
+```
+<<< @/test/markdown/fragments/snippet.js{2}
+```
+
+**Output**
+
+<<< @/test/markdown/fragments/snippet.js{2}
+
 ## Advanced Configuration
 
 VuePress uses [markdown-it](https://github.com/markdown-it/markdown-it) as the markdown renderer. A lot of the extensions above are implemented via custom plugins. You can further customize the `markdown-it` instance using the `markdown` option in `.vuepress/config.js`:

lib/markdown/index.js

@@ -6,6 +6,7 @@ const component = require('./component')
 const hoistScriptStyle = require('./hoist')
 const convertRouterLink = require('./link')
 const containers = require('./containers')
+const snippet = require('./snippet')
 const emoji = require('markdown-it-emoji')
 const anchor = require('markdown-it-anchor')
 const toc = require('markdown-it-table-of-contents')
@@ -24,6 +25,7 @@ module.exports = ({ markdown = {}} = {}) => {
     .use(component)
     .use(highlightLines)
     .use(preWrapper)
+    .use(snippet)
     .use(convertRouterLink, Object.assign({
       target: '_blank',
       rel: 'noopener noreferrer'

lib/markdown/snippet.js

+const fs = require('fs')
+
+module.exports = function snippet (md, options = {}) {
+  const root = options.root || process.cwd()
+  function parser (state, startLine, endLine, silent) {
+    const CH = '<'.charCodeAt(0)
+    const pos = state.bMarks[startLine] + state.tShift[startLine]
+    const max = state.eMarks[startLine]
+
+    // if it's indented more than 3 spaces, it should be a code block
+    if (state.sCount[startLine] - state.blkIndent >= 4) {
+      return false
+    }
+
+    for (let i = 0; i < 3; ++i) {
+      const ch = state.src.charCodeAt(pos + i)
+      if (ch !== CH || pos + i >= max) return false
+    }
+
+    if (silent) {
+      return true
+    }
+
+    const start = pos + 3
+    const end = state.skipSpacesBack(max, pos)
+    const rawPath = state.src.slice(start, end).trim().replace(/^@/, root)
+    const filename = rawPath.split(/[{:\s]/).shift()
+    const content = fs.existsSync(filename) ? fs.readFileSync(filename).toString() : 'Not found: ' + filename
+    const meta = rawPath.replace(filename, '')
+
+    state.line = startLine + 1
+
+    const token = state.push('fence', 'code', 0)
+    token.info = filename.split('.').pop() + meta
+    token.content = content
+    token.markup = '```'
+    token.map = [startLine, startLine + 1]
+
+    return true
+  }
+
+  md.block.ruler.before('fence', 'snippet', parser)
+}

test/markdown/__snapshots__/snippet.spec.js.snap

+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`snippet import snippet 1`] = `
+<pre><code class="language-js">export default function () {
+  // ..
+}</code></pre>
+`;
+
+exports[`snippet import snippet with highlight multiple lines 1`] = `
+<div class="highlight-lines">
+  <div class="highlighted">&nbsp;</div>
+  <div class="highlighted">&nbsp;</div>
+  <div class="highlighted">&nbsp;</div>
+</div>export default function () { // .. }
+`;
+
+exports[`snippet import snippet with highlight single line 1`] = `
+<div class="highlight-lines">
+  <div class="highlighted">&nbsp;</div>
+  <br>
+  <div class="highlighted">&nbsp;</div>
+</div>export default function () { // .. }
+`;

test/markdown/fragments/code-snippet-highlightLines-multiple.md

+<<< @/test/markdown/fragments/snippet.js{1-3}

test/markdown/fragments/code-snippet-highlightLines-single.md

+<<< @/test/markdown/fragments/snippet.js{1,3}

test/markdown/fragments/code-snippet.md

+<<< @/test/markdown/fragments/snippet.js

test/markdown/fragments/snippet.js

+export default function () {
+  // ..
+}

test/markdown/snippet.spec.js

+import { Md, getFragment } from './util'
+import snippet from '@/markdown/snippet.js'
+import highlightLines from '@/markdown/highlightLines.js'
+
+const md = Md().use(snippet)
+const mdH = Md().use(snippet).use(highlightLines)
+
+describe('snippet', () => {
+  test('import snippet', async () => {
+    const input = await getFragment('code-snippet')
+    const output = md.render(input)
+    expect(output).toMatchSnapshot()
+  })
+
+  test('import snippet with highlight single line', async () => {
+    const input = await getFragment('code-snippet-highlightLines-single')
+    const output = mdH.render(input)
+    expect(output).toMatchSnapshot()
+  })
+
+  test('import snippet with highlight multiple lines', async () => {
+    const input = await getFragment('code-snippet-highlightLines-multiple')
+    const output = mdH.render(input)
+    expect(output).toMatchSnapshot()
+  })
+})