[material-ui][docs] Add first batch of v6 migration (#42242)

docs/data/material/migration/migrating-to-v6/migrating-to-v6.md

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+# Migrating to v6
+
+<p class="description">This guide explains how and why to migrate from Material UI v5 to v6.</p>
+
+## Start using the alpha release
+
+In your `package.json` file, change the package version from `latest` to `next`.
+
+```diff title="package.json"
+-"@mui/material": "latest",
++"@mui/material": "next",
+```
+
+Optionally, if you are using one of these packages, you can also change their version to `next`:
+
+- `@mui/icons-material`
+- `@mui/system`
+- `@mui/lab`
+- `@mui/material-nextjs`
+- `@mui/styled-engine-sc`
+- `@mui/utils`
+
+Using `next` ensures your project always uses the latest v6 alpha release.
+Alternatively, you can also target and fix it to a specific version, for example, `6.0.0-alpha.0`.
+
+## Why you should migrate
+
+Material UI v6's biggest highlight is the introduction of Pigment CSS, a next-gen zero-runtime CSS-in-JS library, as an opt-in styling engine.
+Using it will make your project compatible with React Server Components, as well as help reduce its bundle size due to styles being extracted at build time, avoiding client-side recalculation.
+
+As a lesson learned from v5, this major release introduces minimal breaking changes.
+Namely, browser support updates, a Node.js version bump, and the removal of the UMD bundle.
+These updates reduced the Material UI package size by 2.5MB, 25% of the total size, and can be, for the most part, migrated automatically via codemods.
+
+Aside from that, v6 also includes a few quality-of-life improvements regarding styling:
+
+- The `CssVarsProvider` API is now stable. That enables you to rely on CSS variables, allowing for more intricate and performant customization possibilities, along with improved overall developer experience.
+- Support for container queries within the theme.
+- A new theme utility for adding styles to specific color modes.
+
+## Supported browsers and Node versions
+
+The targets of the default bundle have changed in v6.
+
+The exact versions will be pinned on release from the browserslist query `"> 0.5%, last 2 versions, Firefox ESR, not dead, safari >= 15.4, iOS >= 15.4"`.
+
+<!-- #stable-snapshot -->
+
+- Node.js 18 (up from 12)
+- Chrome 109 (up from 90)
+- Edge 121 (up from 91)
+- Firefox 115 (up from 78)
+- Safari 15.4 in both macOS and iOS (up from 14 in macOS and 12.5 in iOS)
+- and more (see [.browserslistrc (`stable` entry)](https://github.com/mui/material-ui/blob/v6.0.0/.browserslistrc#L11))
+
+### Removed support for IE 11
+
+Support for IE 11 is completely removed, by dropping the legacy bundle and all IE 11 related code.
+This allows us to decrease bundle size and keep the scope manageable.
+If you need to support IE 11, you can use Material UI v5's [legacy bundle](https://v5.mui.com/material-ui/guides/minimizing-bundle-size/#legacy-bundle), but it won't get updates or bug fixes.
+
+## Update React & TypeScript version
+
+### Update React
+
+The minimum supported version of React is v17.0.0 (the same as v5).
+Use the snippet below to update your project (replace the `<version>` with the one you want):
+
+<codeblock storageKey="package-manager">
+
+```bash npm
+npm install react@<version> react-dom@<version>
+```
+
+```bash yarn
+yarn add react@<version> react-dom@<version>
+```
+
+```bash pnpm
+pnpm add react@<version> react-dom@<version>
+```
+
+</codeblock>
+
+### Update TypeScript
+
+The minimum supported version of TypeScript has been increased from v3.5 to 4.1.
+
+:::info
+We align with types released by [DefinitelyTyped](https://github.com/DefinitelyTyped/DefinitelyTyped) (published on npm under the `@types` namespace).
+
+We will not change the minimum supported version in a minor version of Material UI.
+However, we recommend not using a TypeScript version older than the lowest supported version by DefinitelyTyped.
+:::
+
+If your project includes these packages, you'll need to update them:
+
+- `@types/react`
+- `@types/react-dom`
+
+:::warning
+Make sure that your application is still running without errors, and commit the changes before continuing to the next step.
+:::
+
+## Breaking changes
+
+:::info
+This list is a work in progress.
+Expect updates as new breaking changes are introduced.
+:::
+
+### UMD bundle was removed
+
+To align with React 19's removal of UMD builds, Material UI has also removed its UMD bundle.
+This results in a reduction of the `@mui/material` package size by 2.5MB or 25% of the total package size.
+
+Instead, using ESM-based CDNs such as [esm.sh](https://esm.sh/) is recommended.
+For alternative installation methods, refer to the [CDN documentation](/material-ui/getting-started/installation/#cdn).
+
+### Chip
+
+Previously, the Chip component lost focus when the escape button was pressed, which differed from how other button-like components work.
+This issue has been resolved, and the Chip now retains focus as expected.
+
+If you want to keep the previous behavior, add a custom `onKeyUp` handler, as shown below:
+
+```js
+import * as React from 'react';
+import Chip from '@mui/material/Chip';
+
+export default function ChipExample() {
+  const chipRef = React.useRef(null);
+  const keyUpHandler = (event) => {
+    if (event.key === 'Escape' && chipRef.current) {
+      chipRef.current.blur();
+    }
+  };
+  return (
+    <Chip
+      label="Chip Outlined"
+      variant="outlined"
+      ref={chipRef}
+      onKeyUp={keyUpHandler}
+    />
+  );
+}
+```
+
+### Loading Button
+
+The `children` passed to the Loading Button component is now wrapped in a `<span>` tag to avoid [issues](https://github.com/mui/material-ui/issues/27853) when using tools to translate websites.
+
+### Grid v2 (Unstable_Grid)
+
+The spacing mechanism was reworked to use the `gap` CSS property.
+This maps better with current layout practices and removes the need for using React Context.
+It brings some breaking changes described in the following sections.
+
+#### Removal of the disableEqualOverflow prop
+
+Previously, the Grid overflowed its parent.
+In v6, this is fixed, with the Grid being contained inside its parent's padding:
+
+<img src="/static/material-ui/migration-v5/grid-overflow-change.png" style="width: 814px;" alt="Before and after of the Grid no longer overflowing its parent in v6." width="1628" height="400" />
+
+This removes the need for the `disableEqualOverflow` prop:
+
+```diff
+- <Grid disableEqualOverflow />
++ <Grid />
+```
+
+#### Spacing is no longer considered inside the Grid item's box
+
+Previously, Grid items included spacing in their boxes.
+In v6, this is fixed:
+
+<img src="/static/material-ui/migration-v5/grid-spacing-change.png" style="width: 814px;" alt="Before and after of the Grid items no longer including spacing in their box." width="1628" height="400" />
+
+:::warning
+Both of these changes might slightly affect your layout.
+Note that the items' position doesn't change.
+We recommend adopting this new behavior and **not trying to replicate the old one**, as this is a more predictable and modern approach.
+:::
+
+### useMediaQuery
+
+The following deprecated types were removed:
+
+- `MuiMediaQueryList`: use `MediaQueryList` (from lib.dom.d.ts) instead.
+- `MuiMediaQueryListEvent`: use `MediaQueryListEvent` (from lib.dom.d.ts) instead.
+- `MuiMediaQueryListListener`: use `(event: MediaQueryListEvent) => void` instead.
+
+## Stabilized APIs
+
+### CssVarsProvider and extendTheme
+
+The `CssVarsProvider` and `extendTheme` APIs are now stable.
+If you already use them in v5, you can now drop the experimental prefix.
+
+```diff
+- import { experimental_extendTheme as extendTheme, Experimental_CssVarsProvider as CssVarsProvider } from '@mui/material/styles';
++ import { extendTheme, CssVarsProvider } from '@mui/material/styles';
+```
+
+Check out the [CSS theme variables page](/material-ui/customization/css-theme-variables/overview/) to learn more about it.
+
+### Add styles for specific color modes
+
+Material UI v6 introduces a new utility for adding styles to specific color modes called `theme.applyStyles`.
+It's designed to replace `theme.palette.mode` when applying light or dark styles.
+
+```diff
+ const MyComponent = styled('button')(({ theme }) => ({
+   padding: '0.5rem 1rem',
+   border: '1px solid,
+-  borderColor: theme.palette.mode === 'dark' ? '#fff' : '#000',
++  borderColor: '#000',
++  ...theme.applyStyles('dark', {
++    borderColor: '#fff',
++  })
+ }))
+```
+
+Use these codemods to migrate your project to `theme.applyStyles`:
+
+```bash
+npx @mui/codemod@next v6.0.0/styled <path/to/folder-or-file>
+npx @mui/codemod@next v6.0.0/sx-prop <path/to/folder-or-file>
+npx @mui/codemod@next v6.0.0/theme-v6 <path/to/theme-file>
+```
+
+:::info
+Run `v6.0.0/theme-v6` against the file that contains the custom `styleOverrides`. Ignore this codemod if you don't have a custom theme.
+:::
+
+## Deprecations
+
+### Components props
+
+The `components` and `componentsProps` props have been deprecated in favor of `slots` and `slotProps`, making the API surface of the components more consistent.
+
+Check out the [deprecations page](/material-ui/migration/migrating-from-deprecated-apis/) to learn which component no longer has these props.
+
+### System props
+
+System props, such as `mt={*}`, `bgcolor={*}`, and others, are deprecated in the Box, Typography, Link, Grid, and Stack components.
+Move all system props into the `sx` prop by using the codemod below:
+
+```bash
+npx @mui/codemod@next v6.0.0/system-props <path/to/folder>
+```
+
+Or do it manually like the example below:
+
+```diff
+- <Button mr={2}>...</Button>
++ <Button sx={{ mr: 2 }}>...</Button>
+```
+
+### Theme component variants
+
+Custom component variants defined in the theme are now merged with the theme style overrides, defined within the `root` slot of the component.
+Update the theme file using the codemod:
+
+```bash
+npx @mui/codemod@next v6.0.0/theme-v6 <path/to/theme>
+```
+
+Or do it manually like the example below:
+
+```diff
+ createTheme({
+   components: {
+     MuiButton: {
+-      variants: [ ... ],
++      styleOverrides: {
++        root: {
++          variants: [ ... ]
++        }
++      }
+     }
+   }
+ })
+```
+
+This reduces the API surface and lets you define variants in other slots of the component.
+
+## Pigment CSS integration (optional)
+
+:::info
+⏳ This section is under construction
+:::