Resolve mdx plugins string format (#72802)

Implements support for passing MDX related plugins as strings instead of
as JS functions, this makes sure you can use MDX plugins with Turbopack.

This still means that e.g. the options have to be serializable, in
testing a few plugins these plugins usually have serializable options
though.

Fixes #71819
Fixes PACK-3345

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packages/next-mdx/index.js

@@ -2,23 +2,24 @@ module.exports =
   (pluginOptions = {}) =>
   (nextConfig = {}) => {
     const extension = pluginOptions.extension || /\.mdx$/
+    const userProvidedMdxOptions = pluginOptions.options
 
     const mdxRsOptions = nextConfig?.experimental?.mdxRs
     const loader = mdxRsOptions
       ? {
           loader: require.resolve('./mdx-rs-loader'),
           options: {
             providerImportSource: 'next-mdx-import-source-file',
-            ...pluginOptions.options,
+            ...userProvidedMdxOptions,
             // mdxRsOptions is a union of boolean and object type of MdxTransformOptions
             ...(mdxRsOptions === true ? {} : mdxRsOptions),
           },
         }
       : {
-          loader: require.resolve('@mdx-js/loader'),
+          loader: require.resolve('./mdx-js-loader'),
           options: {
             providerImportSource: 'next-mdx-import-source-file',
-            ...pluginOptions.options,
+            ...userProvidedMdxOptions,
           },
         }
 

packages/next-mdx/mdx-js-loader.js

@@ -0,0 +1,66 @@
+const mdxLoader = require('@mdx-js/loader')
+
+function interopDefault(mod) {
+  return mod.default || mod
+}
+
+async function importPlugin(plugin, projectRoot) {
+  if (Array.isArray(plugin) && typeof plugin[0] === 'string') {
+    plugin[0] = interopDefault(
+      await import(require.resolve(plugin[0], { paths: [projectRoot] }))
+    )
+  }
+  return plugin
+}
+
+async function getOptions(options, projectRoot) {
+  const {
+    recmaPlugins = [],
+    rehypePlugins = [],
+    remarkPlugins = [],
+    ...rest
+  } = options
+
+  const [updatedRecma, updatedRehype, updatedRemark] = await Promise.all([
+    Promise.all(
+      recmaPlugins.map((plugin) => importPlugin(plugin, projectRoot))
+    ),
+    Promise.all(
+      rehypePlugins.map((plugin) => importPlugin(plugin, projectRoot))
+    ),
+    Promise.all(
+      remarkPlugins.map((plugin) => importPlugin(plugin, projectRoot))
+    ),
+  ])
+
+  return {
+    ...rest,
+    recmaPlugins: updatedRecma,
+    rehypePlugins: updatedRehype,
+    remarkPlugins: updatedRemark,
+  }
+}
+
+module.exports = function nextMdxLoader(...args) {
+  const options = this.getOptions()
+  const callback = this.async().bind(this)
+  const loaderContext = this
+
+  getOptions(options, this.context).then((userProvidedMdxOptions) => {
+    const proxy = new Proxy(loaderContext, {
+      get(target, prop, receiver) {
+        if (prop === 'getOptions') {
+          return () => userProvidedMdxOptions
+        }
+
+        if (prop === 'async') {
+          return () => callback
+        }
+
+        return Reflect.get(target, prop, receiver)
+      },
+    })
+
+    mdxLoader.call(proxy, ...args)
+  })
+}

test/e2e/app-dir/mdx/app/rehype-plugin/page.mdx

@@ -0,0 +1,5 @@
+# Rehype plugin
+
+```math
+C_L
+```

test/e2e/app-dir/mdx/mdx.test.ts

@@ -8,6 +8,7 @@ for (const type of ['with-mdx-rs', 'without-mdx-rs']) {
         '@next/mdx': 'canary',
         '@mdx-js/loader': '^2.2.1',
         '@mdx-js/react': '^2.2.1',
+        'rehype-katex': '7.0.1',
       },
       env: {
         WITH_MDX_RS: type === 'with-mdx-rs' ? 'true' : 'false',
@@ -59,6 +60,14 @@ for (const type of ['with-mdx-rs', 'without-mdx-rs']) {
           '/_next/image?url=%2Ftest.jpg&w=384&q=75'
         )
       })
+
+      if (type === 'without-mdx-rs') {
+        it('should run plugins', async () => {
+          const html = await next.render('/rehype-plugin')
+          expect(html.includes('<mi>C</mi>')).toBe(true)
+          expect(html.includes('<mi>L</mi>')).toBe(true)
+        })
+      }
     })
 
     describe('pages directory', () => {

test/e2e/app-dir/mdx/next.config.js → test/e2e/app-dir/mdx/next.config.mjs

@@ -1,5 +1,10 @@
-const withMDX = require('@next/mdx')({
+import nextMDX from '@next/mdx'
+const withMDX = nextMDX({
   extension: /\.mdx?$/,
+  options: {
+    remarkPlugins: [],
+    rehypePlugins: [['rehype-katex', { strict: true, throwOnError: true }]],
+  },
 })
 
 /**
@@ -12,4 +17,4 @@ const nextConfig = {
   },
 }
 
-module.exports = withMDX(nextConfig)
+export default withMDX(nextConfig)