From b78a7f2f35e554a8647c3262d7f392e68d06febc Mon Sep 17 00:00:00 2001
From: lauren <poteto@users.noreply.github.com>
Date: Mon, 7 Oct 2024 16:25:04 -0400
Subject: [PATCH] [rcr] Re-export useMemoCache in top level React namespace
 (#31139)

In order to support using the compiler on versions of React prior to 19,
we need the ability to statically import `c` (aka useMemoCache) or
fallback to a polyfill supplied by `react-compiler-runtime` (note: this
is a separate npm package, not to be confused with
`react/compiler-runtime`, which is currently a part of react).

To do this we first need to re-export `useMemoCache` under the top level
React namespace again, which is additive and thus non-breaking. Doing so
allows `react-compiler-runtime` to statically either re-export
`React.__COMPILER_RUNTIME.c` or supply a polyfill, without the need for
a dynamic import which is finicky to support due to returning a promise.

In later PRs I will remove `react/compiler-runtime` and update the
compiler to emit imports to `react-compiler-runtime` instead.
---
 packages/react/index.development.js              |  1 +
 packages/react/index.experimental.development.js |  1 +
 packages/react/index.experimental.js             |  1 +
 packages/react/index.fb.js                       |  1 +
 packages/react/index.js                          |  1 +
 packages/react/src/ReactClient.js                |  2 ++
 packages/react/src/ReactCompilerRuntime.js       | 14 ++++++++++++++
 7 files changed, 21 insertions(+)
 create mode 100644 packages/react/src/ReactCompilerRuntime.js

diff --git a/packages/react/index.development.js b/packages/react/index.development.js
index c94c460b97416..bf08db7a58418 100644
--- a/packages/react/index.development.js
+++ b/packages/react/index.development.js
@@ -30,6 +30,7 @@ export type ChildrenArray<+T> = $ReadOnlyArray<ChildrenArray<T>> | T;
 // We can't use export * from in Flow for some reason.
 export {
   __CLIENT_INTERNALS_DO_NOT_USE_OR_WARN_USERS_THEY_CANNOT_UPGRADE,
+  __COMPILER_RUNTIME,
   Children,
   Component,
   Fragment,
diff --git a/packages/react/index.experimental.development.js b/packages/react/index.experimental.development.js
index 4ffcdea0d242e..676b9eea4d9a9 100644
--- a/packages/react/index.experimental.development.js
+++ b/packages/react/index.experimental.development.js
@@ -9,6 +9,7 @@
 
 export {
   __CLIENT_INTERNALS_DO_NOT_USE_OR_WARN_USERS_THEY_CANNOT_UPGRADE,
+  __COMPILER_RUNTIME,
   Children,
   Component,
   Fragment,
diff --git a/packages/react/index.experimental.js b/packages/react/index.experimental.js
index 6f2ab835135c0..ae98e3b91f19c 100644
--- a/packages/react/index.experimental.js
+++ b/packages/react/index.experimental.js
@@ -9,6 +9,7 @@
 
 export {
   __CLIENT_INTERNALS_DO_NOT_USE_OR_WARN_USERS_THEY_CANNOT_UPGRADE,
+  __COMPILER_RUNTIME,
   Children,
   Component,
   Fragment,
diff --git a/packages/react/index.fb.js b/packages/react/index.fb.js
index 1b87e4b2e582f..7999655f30e4b 100644
--- a/packages/react/index.fb.js
+++ b/packages/react/index.fb.js
@@ -9,6 +9,7 @@
 
 export {
   __CLIENT_INTERNALS_DO_NOT_USE_OR_WARN_USERS_THEY_CANNOT_UPGRADE,
+  __COMPILER_RUNTIME,
   act,
   cache,
   Children,
diff --git a/packages/react/index.js b/packages/react/index.js
index 19f256fd73b5b..0c048c4e9c297 100644
--- a/packages/react/index.js
+++ b/packages/react/index.js
@@ -31,6 +31,7 @@ export type ChildrenArray<+T> = $ReadOnlyArray<ChildrenArray<T>> | T;
 // We can't use export * from in Flow for some reason.
 export {
   __CLIENT_INTERNALS_DO_NOT_USE_OR_WARN_USERS_THEY_CANNOT_UPGRADE,
+  __COMPILER_RUNTIME,
   Children,
   Component,
   Fragment,
diff --git a/packages/react/src/ReactClient.js b/packages/react/src/ReactClient.js
index 318d8e648d9d5..ed064fe8031c0 100644
--- a/packages/react/src/ReactClient.js
+++ b/packages/react/src/ReactClient.js
@@ -63,6 +63,7 @@ import ReactSharedInternals from './ReactSharedInternalsClient';
 import {startTransition} from './ReactStartTransition';
 import {act} from './ReactAct';
 import {captureOwnerStack} from './ReactOwnerStack';
+import ReactCompilerRuntime from './ReactCompilerRuntime';
 
 const Children = {
   map,
@@ -109,6 +110,7 @@ export {
   isValidElement,
   ReactVersion as version,
   ReactSharedInternals as __CLIENT_INTERNALS_DO_NOT_USE_OR_WARN_USERS_THEY_CANNOT_UPGRADE,
+  ReactCompilerRuntime as __COMPILER_RUNTIME,
   // Concurrent Mode
   useTransition,
   startTransition,
diff --git a/packages/react/src/ReactCompilerRuntime.js b/packages/react/src/ReactCompilerRuntime.js
new file mode 100644
index 0000000000000..a19d05596863e
--- /dev/null
+++ b/packages/react/src/ReactCompilerRuntime.js
@@ -0,0 +1,14 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+import {useMemoCache} from './ReactHooks';
+
+export default {
+  c: useMemoCache,
+};