Expose prerender() for SSG in stable (#31298)

When we added `renderToReadableStream` we added the `allReady` helper to
make it easier to do SSG rendering but it's kind of awkward to wire up
that way. Since we're also discouraging `renderToString` in React 19 the
cliff is kind of awkward. ([As noted by
Docusaurus.](https://github.com/facebook/react/pull/24752#issuecomment-2178309299))

The idea of the `react-dom/static` `prerender` API was that this would
be the replacement for SSG rendering. Awkwardly this entry point
actually already exists in stable but it has only `undefined` exports.

Since then we've also added other useful heuristics into the `prerender`
branch that makes this really the favored and easiest to use API for the
prerender (SSG/ISR) use case.

`prerender` is also used for Partial Prerendering but that part is still
experimental.

However, we can expose only the `prerender` API on `react-dom/static`
without it returning the `postponeState`. Instead the stream is on
`prelude`. The naming is a bit awkward if you don't consider resuming
but it's the same thing.

It's really just `renderToReadable` stream with automatic `allReady` and
better heuristics for prerendering.

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

@@ -32,9 +32,7 @@ describe('ReactDOMFizzStatic', () => {
     React = require('react');
     ReactDOM = require('react-dom');
     ReactDOMClient = require('react-dom/client');
-    if (__EXPERIMENTAL__) {
-      ReactDOMFizzStatic = require('react-dom/static');
-    }
+    ReactDOMFizzStatic = require('react-dom/static');
     Stream = require('stream');
     Suspense = React.Suspense;
 
@@ -212,7 +210,6 @@ describe('ReactDOMFizzStatic', () => {
     return readText(text);
   }
 
-  // @gate experimental
   it('should render a fully static document, send it and then hydrate it', async () => {
     function App() {
       return (
@@ -230,7 +227,11 @@ describe('ReactDOMFizzStatic', () => {
 
     const result = await promise;
 
-    expect(result.postponed).toBe(null);
+    expect(result.postponed).toBe(
+      gate(flags => flags.enableHalt || flags.enablePostpone)
+        ? null
+        : undefined,
+    );
 
     await act(async () => {
       result.prelude.pipe(writable);
@@ -244,7 +245,6 @@ describe('ReactDOMFizzStatic', () => {
     expect(getVisibleChildren(container)).toEqual(<div>Hello</div>);
   });
 
-  // @gate experimental
   it('should support importMap option', async () => {
     const importMap = {
       foo: 'path/to/foo.js',
@@ -265,7 +265,6 @@ describe('ReactDOMFizzStatic', () => {
     ]);
   });
 
-  // @gate experimental
   it('supports onHeaders', async () => {
     let headers;
     function onHeaders(x) {
@@ -300,7 +299,7 @@ describe('ReactDOMFizzStatic', () => {
     expect(getVisibleChildren(container)).toEqual('hello');
   });
 
-  // @gate experimental && enablePostpone
+  // @gate enablePostpone
   it('includes stylesheet preloads in onHeaders when postponing in the Shell', async () => {
     let headers;
     function onHeaders(x) {
@@ -336,7 +335,6 @@ describe('ReactDOMFizzStatic', () => {
     expect(getVisibleChildren(container)).toEqual(undefined);
   });
 
-  // @gate experimental
   it('will prerender Suspense fallbacks before children', async () => {
     const values = [];
     function Indirection({children}) {

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

@@ -42,9 +42,7 @@ describe('ReactDOMFizzStaticBrowser', () => {
     React = require('react');
     ReactDOM = require('react-dom');
     ReactDOMFizzServer = require('react-dom/server.browser');
-    if (__EXPERIMENTAL__) {
-      ReactDOMFizzStatic = require('react-dom/static.browser');
-    }
+    ReactDOMFizzStatic = require('react-dom/static.browser');
     Suspense = React.Suspense;
     container = document.createElement('div');
     document.body.appendChild(container);
@@ -131,7 +129,6 @@ describe('ReactDOMFizzStaticBrowser', () => {
     await insertNodesAndExecuteScripts(temp, container, null);
   }
 
-  // @gate experimental
   it('should call prerender', async () => {
     const result = await serverAct(() =>
       ReactDOMFizzStatic.prerender(<div>hello world</div>),
@@ -140,7 +137,6 @@ describe('ReactDOMFizzStaticBrowser', () => {
     expect(prelude).toMatchInlineSnapshot(`"<div>hello world</div>"`);
   });
 
-  // @gate experimental
   it('should emit DOCTYPE at the root of the document', async () => {
     const result = await serverAct(() =>
       ReactDOMFizzStatic.prerender(
@@ -155,7 +151,6 @@ describe('ReactDOMFizzStaticBrowser', () => {
     );
   });
 
-  // @gate experimental
   it('should emit bootstrap script src at the end', async () => {
     const result = await serverAct(() =>
       ReactDOMFizzStatic.prerender(<div>hello world</div>, {
@@ -170,7 +165,6 @@ describe('ReactDOMFizzStaticBrowser', () => {
     );
   });
 
-  // @gate experimental
   it('emits all HTML as one unit', async () => {
     let hasLoaded = false;
     let resolve;
@@ -202,7 +196,6 @@ describe('ReactDOMFizzStaticBrowser', () => {
     expect(prelude).toMatchInlineSnapshot(`"<div><!--$-->Done<!--/$--></div>"`);
   });
 
-  // @gate experimental
   it('should reject the promise when an error is thrown at the root', async () => {
     const reportedErrors = [];
     let caughtError = null;
@@ -226,7 +219,6 @@ describe('ReactDOMFizzStaticBrowser', () => {
     expect(reportedErrors).toEqual([theError]);
   });
 
-  // @gate experimental
   it('should reject the promise when an error is thrown inside a fallback', async () => {
     const reportedErrors = [];
     let caughtError = null;
@@ -252,7 +244,6 @@ describe('ReactDOMFizzStaticBrowser', () => {
     expect(reportedErrors).toEqual([theError]);
   });
 
-  // @gate experimental
   it('should not error the stream when an error is thrown inside suspense boundary', async () => {
     const reportedErrors = [];
     const result = await serverAct(() =>
@@ -275,7 +266,6 @@ describe('ReactDOMFizzStaticBrowser', () => {
     expect(reportedErrors).toEqual([theError]);
   });
 
-  // @gate experimental
   it('should be able to complete by aborting even if the promise never resolves', async () => {
     const errors = [];
     const controller = new AbortController();
@@ -306,7 +296,6 @@ describe('ReactDOMFizzStaticBrowser', () => {
     expect(errors).toEqual(['The operation was aborted.']);
   });
 
-  // @gate experimental
   // @gate !enableHalt
   it('should reject if aborting before the shell is complete and enableHalt is disabled', async () => {
     const errors = [];
@@ -376,7 +365,6 @@ describe('ReactDOMFizzStaticBrowser', () => {
     expect(content).toBe('');
   });
 
-  // @gate experimental
   it('should be able to abort before something suspends', async () => {
     const errors = [];
     const controller = new AbortController();
@@ -419,7 +407,6 @@ describe('ReactDOMFizzStaticBrowser', () => {
     }
   });
 
-  // @gate experimental
   // @gate !enableHalt
   it('should reject if passing an already aborted signal and enableHalt is disabled', async () => {
     const errors = [];
@@ -493,7 +480,6 @@ describe('ReactDOMFizzStaticBrowser', () => {
     expect(content).toBe('');
   });
 
-  // @gate experimental
   it('supports custom abort reasons with a string', async () => {
     const promise = new Promise(r => {});
     function Wait() {
@@ -536,7 +522,6 @@ describe('ReactDOMFizzStaticBrowser', () => {
     expect(errors).toEqual(['foobar', 'foobar']);
   });
 
-  // @gate experimental
   it('supports custom abort reasons with an Error', async () => {
     const promise = new Promise(r => {});
     function Wait() {
@@ -1610,7 +1595,6 @@ describe('ReactDOMFizzStaticBrowser', () => {
     );
   });
 
-  // @gate experimental
   it('logs an error if onHeaders throws but continues the prerender', async () => {
     const errors = [];
     function onError(error) {
@@ -1627,7 +1611,11 @@ describe('ReactDOMFizzStaticBrowser', () => {
         onError,
       }),
     );
-    expect(prerendered.postponed).toBe(null);
+    expect(prerendered.postponed).toBe(
+      gate(flags => flags.enableHalt || flags.enablePostpone)
+        ? null
+        : undefined,
+    );
     expect(errors).toEqual(['bad onHeaders']);
 
     await readIntoContainer(prerendered.prelude);

packages/react-dom/src/server/ReactDOMFizzStaticBrowser.js

@@ -38,6 +38,8 @@ import {
   createRootFormatContext,
 } from 'react-dom-bindings/src/server/ReactFizzConfigDOM';
 
+import {enablePostpone, enableHalt} from 'shared/ReactFeatureFlags';
+
 import {ensureCorrectIsomorphicReactVersion} from '../shared/ensureCorrectIsomorphicReactVersion';
 ensureCorrectIsomorphicReactVersion();
 
@@ -85,10 +87,15 @@ function prerender(
         {highWaterMark: 0},
       );
 
-      const result = {
-        postponed: getPostponedState(request),
-        prelude: stream,
-      };
+      const result: StaticResult =
+        enablePostpone || enableHalt
+          ? {
+              postponed: getPostponedState(request),
+              prelude: stream,
+            }
+          : ({
+              prelude: stream,
+            }: any);
       resolve(result);
     }
 

packages/react-dom/src/server/ReactDOMFizzStaticEdge.js

@@ -38,6 +38,8 @@ import {
   createRootFormatContext,
 } from 'react-dom-bindings/src/server/ReactFizzConfigDOM';
 
+import {enablePostpone, enableHalt} from 'shared/ReactFeatureFlags';
+
 import {ensureCorrectIsomorphicReactVersion} from '../shared/ensureCorrectIsomorphicReactVersion';
 ensureCorrectIsomorphicReactVersion();
 
@@ -85,10 +87,15 @@ function prerender(
         {highWaterMark: 0},
       );
 
-      const result = {
-        postponed: getPostponedState(request),
-        prelude: stream,
-      };
+      const result: StaticResult =
+        enablePostpone || enableHalt
+          ? {
+              postponed: getPostponedState(request),
+              prelude: stream,
+            }
+          : ({
+              prelude: stream,
+            }: any);
       resolve(result);
     }
 

packages/react-dom/src/server/ReactDOMFizzStaticNode.js

@@ -39,6 +39,8 @@ import {
   createRootFormatContext,
 } from 'react-dom-bindings/src/server/ReactFizzConfigDOM';
 
+import {enablePostpone, enableHalt} from 'shared/ReactFeatureFlags';
+
 import {ensureCorrectIsomorphicReactVersion} from '../shared/ensureCorrectIsomorphicReactVersion';
 ensureCorrectIsomorphicReactVersion();
 
@@ -94,10 +96,15 @@ function prerenderToNodeStream(
       });
       const writable = createFakeWritable(readable);
 
-      const result = {
-        postponed: getPostponedState(request),
-        prelude: readable,
-      };
+      const result: StaticResult =
+        enablePostpone || enableHalt
+          ? {
+              postponed: getPostponedState(request),
+              prelude: readable,
+            }
+          : ({
+              prelude: readable,
+            }: any);
       resolve(result);
     }
     const resumableState = createResumableState(

packages/react-dom/src/server/react-dom-server.browser.stable.js

@@ -8,3 +8,4 @@
  */
 
 export {renderToReadableStream, version} from './ReactDOMFizzServerBrowser.js';
+export {prerender} from './ReactDOMFizzStaticBrowser.js';

packages/react-dom/src/server/react-dom-server.edge.stable.js

@@ -8,3 +8,4 @@
  */
 
 export {renderToReadableStream, version} from './ReactDOMFizzServerEdge.js';
+export {prerender} from './ReactDOMFizzStaticEdge.js';

packages/react-dom/src/server/react-dom-server.node.stable.js

@@ -8,3 +8,4 @@
  */
 
 export {renderToPipeableStream, version} from './ReactDOMFizzServerNode.js';
+export {prerenderToNodeStream} from './ReactDOMFizzStaticNode.js';