Add docs for modularize-imports.

docs/advanced-features/compiler.md

@@ -203,6 +203,89 @@ module.exports = {
 
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+### Modularize Imports
+
+Allows to modularize imports, similar to [babel-plugin-transform-imports](https://www.npmjs.com/package/babel-plugin-transform-imports).
+
+Transforms member style imports:
+
+```js
+import { Row, Grid as MyGrid } from 'react-bootstrap'
+import { merge } from 'lodash'
+```
+
+...into default style imports:
+
+```js
+import Row from 'react-bootstrap/lib/Row'
+import MyGrid from 'react-bootstrap/lib/Grid'
+import merge from 'lodash/merge'
+```
+
+Config for the above transform:
+
+```js
+// next.config.js
+module.exports = {
+  experimental: {
+    modularizeImports: {
+      'react-bootstrap': {
+        transform: 'react-bootstrap/lib/{{member}}',
+      },
+      lodash: {
+        transform: 'lodash/{{member}}',
+      },
+    },
+  },
+}
+```
+
+Advanced transformations:
+
+- Using regular expressions
+
+Similar to `babel-plugin-transform-imports`, but the transform is templated with [handlebars](https://docs.rs/handlebars) and regular expressions are in Rust [regex](https://docs.rs/regex/latest/regex/) crate's syntax.
+
+The config:
+
+```js
+// next.config.js
+module.exports = {
+  experimental: {
+    modularizeImports: {
+      'my-library/?(((\\w*)?/?)*)': {
+        transform: 'my-library/{{ matches.[1] }}/{{member}}',
+      },
+    },
+  },
+}
+```
+
+Cause this code:
+
+```js
+import { MyModule } from 'my-library'
+import { App } from 'my-library/components'
+import { Header, Footer } from 'my-library/components/App'
+```
+
+To become:
+
+```js
+import MyModule from 'my-library/MyModule'
+import App from 'my-library/components/App'
+import Header from 'my-library/components/App/Header'
+import Footer from 'my-library/components/App/Footer'
+```
+
+- Handlebars templating
+
+This transform uses [handlebars](https://docs.rs/handlebars) to template the replacement import path in the `transform` field. These variables and helper functions are available:
+
+1. `matches`: Has type `string[]`. All groups matched by the regular expression. `matches.[0]` is the full match.
+2. `member`: Has type `string`. The name of the member import.
+3. `lowerCase`, `upperCase`, `camelCase`: Helper functions to convert a string to lower, upper or camel cases.
+
 ## Unsupported Features
 
 When your application has a `.babelrc` file, Next.js will automatically fall back to using Babel for transforming individual files. This ensures backwards compatibility with existing applications that leverage custom Babel plugins.