Add codemod documentation

docs/advanced-features/codemods.md

@@ -0,0 +1,149 @@
+---
+description: Use codemods to update your codebase when upgrading Next.js to the latest version
+---
+
+# Next.js Codemods
+
+Next.js provides Codemod transformations to help upgrade your Next.js codebase when a feature is deprecated.
+
+Codemods are transformations that run on your codebase programmatically. This allows for a large amount of changes to be applied without having to manually go through every file.
+
+## Usage
+
+`npx @next/codemod <transform> <path>`
+
+- `transform` - name of transform, see available transforms below.
+- `path` - files or directory to transform
+- `--dry` Do a dry-run, no code will be edited
+- `--print` Prints the changed output for comparison
+
+## Next.js 9
+
+### `name-default-component`
+
+Transforms anonymous components into named components to make sure they work with [Fast Refresh](https://nextjs.org/blog/next-9-4#fast-refresh).
+
+For example
+
+```jsx
+// my-component.js
+export default function () {
+  return <div>Hello World</div>
+}
+```
+
+Transforms into:
+
+```jsx
+// my-component.js
+export default function MyComponent() {
+  return <div>Hello World</div>
+}
+```
+
+The component will have a camel cased name based on the name of the file, and it also works with arrow functions.
+
+#### Usage
+
+Go to your project
+
+```
+cd path-to-your-project/
+```
+
+Run the codemod:
+
+```
+npx @next/codemod name-default-component
+```
+
+### `withamp-to-config`
+
+Transforms the `withAmp` HOC into Next.js 9 page configuration.
+
+For example:
+
+```js
+// Before
+import { withAmp } from 'next/amp'
+
+function Home() {
+  return <h1>My AMP Page</h1>
+}
+
+export default withAmp(Home)
+```
+
+```js
+// After
+export default function Home() {
+  return <h1>My AMP Page</h1>
+}
+
+export const config = {
+  amp: true,
+}
+```
+
+#### Usage
+
+Go to your project
+
+```
+cd path-to-your-project/
+```
+
+Run the codemod:
+
+```
+npx @next/codemod withamp-to-config
+```
+
+## Next.js 6
+
+### `url-to-withrouter`
+
+Transforms the deprecated automatically injected `url` property on top level pages to using `withRouter` and the `router` property it injects. Read more here: [err.sh/next.js/url-deprecated](https://err.sh/next.js/url-deprecated)
+
+For example:
+
+```js
+// From
+import React from 'react'
+export default class extends React.Component {
+  render() {
+    const { pathname } = this.props.url
+    return <div>Current pathname: {pathname}</div>
+  }
+}
+```
+
+```js
+// To
+import React from 'react'
+import { withRouter } from 'next/router'
+export default withRouter(
+  class extends React.Component {
+    render() {
+      const { pathname } = this.props.router
+      return <div>Current pathname: {pathname}</div>
+    }
+  }
+)
+```
+
+This is just one case. All the cases that are transformed (and tested) can be found in the [`__testfixtures__` directory](./transforms/__testfixtures__/url-to-withrouter).
+
+#### Usage
+
+Go to your project
+
+```
+cd path-to-your-project/
+```
+
+Run the codemod:
+
+```
+npx @next/codemod url-to-withrouter
+```

docs/manifest.json

@@ -176,6 +176,10 @@
             {
               "title": "Debugging",
               "path": "/docs/advanced-features/debugging.md"
+            },
+            {
+              "title": "Codemods",
+              "path": "/docs/advanced-features/codemods.md"
             }
           ]
         },