Add React 19 support (#3543)

This PR fixes an issue where `@headlessui/react` was not compatible with
React 19.

We made sure that accessing `ref`s is safe and works in React 18 and
React 19. We also made sure to include React 19 as a valid version in
the peer dependencies. For now, we also allowed the RC versions of React
and React DOM.

packages/@headlessui-react/CHANGELOG.md

@@ -7,7 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-- Nothing yet!
+### Added
+
+- Add React 19 support ([#3543](https://github.com/tailwindlabs/headlessui/pull/3543))
 
 ## [2.1.10] - 2024-10-10
 

packages/@headlessui-react/package.json

@@ -42,8 +42,8 @@
     "clean": "rimraf ./dist"
   },
   "peerDependencies": {
-    "react": "^18",
-    "react-dom": "^18"
+    "react": "^18 || ^19 || ^19.0.0-rc",
+    "react-dom": "^18 || ^19 || ^19.0.0-rc"
   },
   "devDependencies": {
     "@testing-library/react": "^15.0.7",

packages/@headlessui-react/src/utils/render.ts

@@ -1,4 +1,4 @@
-import {
+import React, {
   Fragment,
   cloneElement,
   createElement,
@@ -257,7 +257,7 @@ function _render<TTag extends ElementType, TSlot>(
             mergedProps,
             dataAttributes,
             refRelatedProps,
-            { ref: mergeRefs((resolvedChildren as any).ref, refRelatedProps.ref) },
+            { ref: mergeRefs(getElementRef(resolvedChildren), refRelatedProps.ref) },
             classNameProps
           )
         )
@@ -460,3 +460,8 @@ function omit<T extends Record<any, any>>(object: T, keysToOmit: string[] = [])
   }
   return clone
 }
+
+function getElementRef(element: React.ReactElement) {
+  // @ts-expect-error
+  return React.version.split('.')[0] >= '19' ? element.props.ref : element.ref
+}