Scaffolding for useFormState (#27270)

This exposes, but does not yet implement, a new experimental API called
useFormState. It's gated behind the enableAsyncActions flag.

useFormState has a similar signature to useReducer, except instead of a
reducer it accepts an (async) action function. React will wait until the
promise resolves before updating the state:

```js
async function action(prevState, payload) {
  // ..
}
const [state, dispatch] = useFormState(action, initialState)
```

When used in combination with Server Actions, it will also support
progressive enhancement — a form that is submitted before it has
hydrated will have its state transferred to the next page. However, like
the other action-related hooks, it works with fully client-driven
actions, too.

Author: acdlite

.eslintrc.js

@@ -456,6 +456,7 @@ module.exports = {
     $ReadOnlyArray: 'readonly',
     $ArrayBufferView: 'readonly',
     $Shape: 'readonly',
+    ReturnType: 'readonly',
     AnimationFrameID: 'readonly',
     // For Flow type annotation. Only `BigInt` is valid at runtime.
     bigint: 'readonly',

packages/react-dom-bindings/src/shared/ReactDOMFormActions.js

@@ -74,3 +74,17 @@ export function useFormStatus(): FormStatus {
     return dispatcher.useHostTransitionStatus();
   }
 }
+
+export function useFormState<S, P>(
+  action: (S, P) => S,
+  initialState: S,
+  url?: string,
+): [S, (P) => void] {
+  if (!(enableFormActions && enableAsyncActions)) {
+    throw new Error('Not implemented.');
+  } else {
+    const dispatcher = resolveDispatcher();
+    // $FlowFixMe[not-a-function] This is unstable, thus optional
+    return dispatcher.useFormState(action, initialState, url);
+  }
+}

packages/react-dom/index.classic.fb.js

@@ -32,6 +32,7 @@ export {
   unstable_renderSubtreeIntoContainer,
   unstable_runWithPriority, // DO NOT USE: Temporarily exposed to migrate off of Scheduler.runWithPriority.
   useFormStatus as experimental_useFormStatus,
+  useFormState as experimental_useFormState,
   prefetchDNS,
   preconnect,
   preload,

packages/react-dom/index.experimental.js

@@ -21,6 +21,7 @@ export {
   unstable_renderSubtreeIntoContainer,
   unstable_runWithPriority, // DO NOT USE: Temporarily exposed to migrate off of Scheduler.runWithPriority.
   useFormStatus as experimental_useFormStatus,
+  useFormState as experimental_useFormState,
   prefetchDNS,
   preconnect,
   preload,

packages/react-dom/index.js

@@ -24,6 +24,7 @@ export {
   unstable_renderSubtreeIntoContainer,
   unstable_runWithPriority, // DO NOT USE: Temporarily exposed to migrate off of Scheduler.runWithPriority.
   useFormStatus as experimental_useFormStatus,
+  useFormState as experimental_useFormState,
   prefetchDNS,
   preconnect,
   preload,

packages/react-dom/index.modern.fb.js

@@ -17,6 +17,7 @@ export {
   unstable_createEventHandle,
   unstable_runWithPriority, // DO NOT USE: Temporarily exposed to migrate off of Scheduler.runWithPriority.
   useFormStatus as experimental_useFormStatus,
+  useFormState as experimental_useFormState,
   prefetchDNS,
   preconnect,
   preload,

packages/react-dom/server-rendering-stub.js

@@ -23,5 +23,6 @@ export {
   preload,
   preinit,
   experimental_useFormStatus,
+  experimental_useFormState,
   unstable_batchedUpdates,
 } from './src/server/ReactDOMServerRenderingStub';

packages/react-dom/src/__tests__/ReactDOMFizzForm-test.js

@@ -23,6 +23,7 @@ let ReactDOMServer;
 let ReactDOMClient;
 let useFormStatus;
 let useOptimistic;
+let useFormState;
 
 describe('ReactDOMFizzForm', () => {
   beforeEach(() => {
@@ -31,6 +32,7 @@ describe('ReactDOMFizzForm', () => {
     ReactDOMServer = require('react-dom/server.browser');
     ReactDOMClient = require('react-dom/client');
     useFormStatus = require('react-dom').experimental_useFormStatus;
+    useFormState = require('react-dom').experimental_useFormState;
     useOptimistic = require('react').experimental_useOptimistic;
     act = require('internal-test-utils').act;
     container = document.createElement('div');
@@ -470,6 +472,28 @@ describe('ReactDOMFizzForm', () => {
     expect(container.textContent).toBe('hi');
   });
 
+  // @gate enableFormActions
+  // @gate enableAsyncActions
+  it('useFormState returns initial state', async () => {
+    async function action(state) {
+      return state;
+    }
+
+    function App() {
+      const [state] = useFormState(action, 0);
+      return state;
+    }
+
+    const stream = await ReactDOMServer.renderToReadableStream(<App />);
+    await readIntoContainer(stream);
+    expect(container.textContent).toBe('0');
+
+    await act(async () => {
+      ReactDOMClient.hydrateRoot(container, <App />);
+    });
+    expect(container.textContent).toBe('0');
+  });
+
   // @gate enableFormActions
   it('can provide a custom action on the server for actions', async () => {
     const ref = React.createRef();

packages/react-dom/src/__tests__/ReactDOMForm-test.js

@@ -40,6 +40,7 @@ describe('ReactDOMForm', () => {
   let startTransition;
   let textCache;
   let useFormStatus;
+  let useFormState;
 
   beforeEach(() => {
     jest.resetModules();
@@ -53,6 +54,7 @@ describe('ReactDOMForm', () => {
     Suspense = React.Suspense;
     startTransition = React.startTransition;
     useFormStatus = ReactDOM.experimental_useFormStatus;
+    useFormState = ReactDOM.experimental_useFormState;
     container = document.createElement('div');
     document.body.appendChild(container);
 
@@ -969,4 +971,24 @@ describe('ReactDOMForm', () => {
       'A React form was unexpectedly submitted. If you called form.submit()',
     );
   });
+
+  // @gate enableFormActions
+  // @gate enableAsyncActions
+  test('useFormState exists', async () => {
+    // TODO: Not yet implemented. This just tests that the API is wired up.
+
+    async function action(state) {
+      return state;
+    }
+
+    function App() {
+      const [state] = useFormState(action, 0);
+      return <Text text={state} />;
+    }
+
+    const root = ReactDOMClient.createRoot(container);
+    await act(() => root.render(<App />));
+    assertLog([0]);
+    expect(container.textContent).toBe('0');
+  });
 });

packages/react-dom/src/client/ReactDOM.js

@@ -63,7 +63,10 @@ export {
   preinit,
   preinitModule,
 } from '../shared/ReactDOMFloat';
-export {useFormStatus} from 'react-dom-bindings/src/shared/ReactDOMFormActions';
+export {
+  useFormStatus,
+  useFormState,
+} from 'react-dom-bindings/src/shared/ReactDOMFormActions';
 
 if (__DEV__) {
   if (