[Fizz] Track postponed holes in the prerender pass (facebook#27317)

This is basically the implementation for the prerender pass.

Instead of forking basically the whole implementation for prerender, I
just add a conditional field on the request. If it's `null` it behaves
like before. If it's non-`null` then instead of triggering client
rendered boundaries it triggers those into a "postponed" state which is
basically just a variant of "pending". It's supposed to be filled in
later.

It also builds up a serializable tree of which path can be followed to
find the holes. This is basically a reverse `KeyPath` tree.

It is unfortunate that this approach adds more code to the regular Fizz
builds but in practice. It seems like this side is not going to add much
code and we might instead just want to merge the builds so that it's
smaller when you have `prerender` and `resume` in the same bundle -
which I think will be common in practice.

This just implements the prerender side, and not the resume side, which
is why the tests have a TODO. That's in a follow up PR.

packages/react-dom/npm/server.node.js

@@ -15,6 +15,6 @@ exports.renderToStaticMarkup = l.renderToStaticMarkup;
 exports.renderToNodeStream = l.renderToNodeStream;
 exports.renderToStaticNodeStream = l.renderToStaticNodeStream;
 exports.renderToPipeableStream = s.renderToPipeableStream;
-if (s.resume) {
-  exports.resume = s.resume;
+if (s.resumeToPipeableStream) {
+  exports.resumeToPipeableStream = s.resumeToPipeableStream;
 }

packages/react-dom/server.node.js

@@ -43,8 +43,8 @@ export function renderToPipeableStream() {
   );
 }
 
-export function resume() {
-  return require('./src/server/react-dom-server.node').resume.apply(
+export function resumeToPipeableStream() {
+  return require('./src/server/react-dom-server.node').resumeToPipeableStream.apply(
     this,
     arguments,
   );

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

@@ -14,6 +14,7 @@ import {
   mergeOptions,
   stripExternalRuntimeInNodes,
   withLoadingReadyState,
+  getVisibleChildren,
 } from '../test-utils/FizzTestUtils';
 
 let JSDOM;
@@ -23,6 +24,7 @@ let React;
 let ReactDOM;
 let ReactDOMClient;
 let ReactDOMFizzServer;
+let ReactDOMFizzStatic;
 let Suspense;
 let SuspenseList;
 let useSyncExternalStore;
@@ -77,6 +79,9 @@ describe('ReactDOMFizzServer', () => {
     ReactDOM = require('react-dom');
     ReactDOMClient = require('react-dom/client');
     ReactDOMFizzServer = require('react-dom/server');
+    if (__EXPERIMENTAL__) {
+      ReactDOMFizzStatic = require('react-dom/static');
+    }
     Stream = require('stream');
     Suspense = React.Suspense;
     use = React.use;
@@ -289,46 +294,6 @@ describe('ReactDOMFizzServer', () => {
     }, document);
   }
 
-  function getVisibleChildren(element) {
-    const children = [];
-    let node = element.firstChild;
-    while (node) {
-      if (node.nodeType === 1) {
-        if (
-          node.tagName !== 'SCRIPT' &&
-          node.tagName !== 'script' &&
-          node.tagName !== 'TEMPLATE' &&
-          node.tagName !== 'template' &&
-          !node.hasAttribute('hidden') &&
-          !node.hasAttribute('aria-hidden')
-        ) {
-          const props = {};
-          const attributes = node.attributes;
-          for (let i = 0; i < attributes.length; i++) {
-            if (
-              attributes[i].name === 'id' &&
-              attributes[i].value.includes(':')
-            ) {
-              // We assume this is a React added ID that's a non-visual implementation detail.
-              continue;
-            }
-            props[attributes[i].name] = attributes[i].value;
-          }
-          props.children = getVisibleChildren(node);
-          children.push(React.createElement(node.tagName.toLowerCase(), props));
-        }
-      } else if (node.nodeType === 3) {
-        children.push(node.data);
-      }
-      node = node.nextSibling;
-    }
-    return children.length === 0
-      ? undefined
-      : children.length === 1
-      ? children[0]
-      : children;
-  }
-
   function resolveText(text) {
     const record = textCache.get(text);
     if (record === undefined) {
@@ -6227,4 +6192,60 @@ describe('ReactDOMFizzServer', () => {
       );
     },
   );
+
+  // @gate enablePostpone
+  it('supports postponing in prerender and resuming later', async () => {
+    let prerendering = true;
+    function Postpone() {
+      if (prerendering) {
+        React.unstable_postpone();
+      }
+      return 'Hello';
+    }
+
+    function App() {
+      return (
+        <div>
+          <Suspense fallback="Loading...">
+            <Postpone />
+          </Suspense>
+        </div>
+      );
+    }
+
+    const prerendered = await ReactDOMFizzStatic.prerenderToNodeStream(<App />);
+    expect(prerendered.postponed).not.toBe(null);
+
+    prerendering = false;
+
+    const resumed = ReactDOMFizzServer.resumeToPipeableStream(
+      <App />,
+      prerendered.postponed,
+    );
+
+    // Create a separate stream so it doesn't close the writable. I.e. simple concat.
+    const preludeWritable = new Stream.PassThrough();
+    preludeWritable.setEncoding('utf8');
+    preludeWritable.on('data', chunk => {
+      writable.write(chunk);
+    });
+
+    await act(() => {
+      prerendered.prelude.pipe(preludeWritable);
+    });
+
+    expect(getVisibleChildren(container)).toEqual(<div>Loading...</div>);
+
+    const b = new Stream.PassThrough();
+    b.setEncoding('utf8');
+    b.on('data', chunk => {
+      writable.write(chunk);
+    });
+
+    await act(() => {
+      resumed.pipe(writable);
+    });
+
+    // TODO: expect(getVisibleChildren(container)).toEqual(<div>Hello</div>);
+  });
 });

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

@@ -9,23 +9,37 @@
 
 'use strict';
 
+import {
+  getVisibleChildren,
+  insertNodesAndExecuteScripts,
+} from '../test-utils/FizzTestUtils';
+
 // Polyfills for test environment
 global.ReadableStream =
   require('web-streams-polyfill/ponyfill/es6').ReadableStream;
 global.TextEncoder = require('util').TextEncoder;
 
 let React;
+let ReactDOMFizzServer;
 let ReactDOMFizzStatic;
 let Suspense;
+let container;
 
 describe('ReactDOMFizzStaticBrowser', () => {
   beforeEach(() => {
     jest.resetModules();
     React = require('react');
+    ReactDOMFizzServer = require('react-dom/server.browser');
     if (__EXPERIMENTAL__) {
       ReactDOMFizzStatic = require('react-dom/static.browser');
     }
     Suspense = React.Suspense;
+    container = document.createElement('div');
+    document.body.appendChild(container);
+  });
+
+  afterEach(() => {
+    document.body.removeChild(container);
   });
 
   const theError = new Error('This is an error');
@@ -37,6 +51,36 @@ describe('ReactDOMFizzStaticBrowser', () => {
     throw theInfinitePromise;
   }
 
+  function concat(streamA, streamB) {
+    const readerA = streamA.getReader();
+    const readerB = streamB.getReader();
+    return new ReadableStream({
+      start(controller) {
+        function readA() {
+          readerA.read().then(({done, value}) => {
+            if (done) {
+              readB();
+              return;
+            }
+            controller.enqueue(value);
+            readA();
+          });
+        }
+        function readB() {
+          readerB.read().then(({done, value}) => {
+            if (done) {
+              controller.close();
+              return;
+            }
+            controller.enqueue(value);
+            readB();
+          });
+        }
+        readA();
+      },
+    });
+  }
+
   async function readContent(stream) {
     const reader = stream.getReader();
     let content = '';
@@ -49,6 +93,21 @@ describe('ReactDOMFizzStaticBrowser', () => {
     }
   }
 
+  async function readIntoContainer(stream) {
+    const reader = stream.getReader();
+    let result = '';
+    while (true) {
+      const {done, value} = await reader.read();
+      if (done) {
+        break;
+      }
+      result += Buffer.from(value).toString('utf8');
+    }
+    const temp = document.createElement('div');
+    temp.innerHTML = result;
+    insertNodesAndExecuteScripts(temp, container, null);
+  }
+
   // @gate experimental
   it('should call prerender', async () => {
     const result = await ReactDOMFizzStatic.prerender(<div>hello world</div>);
@@ -394,4 +453,82 @@ describe('ReactDOMFizzStaticBrowser', () => {
 
     expect(errors).toEqual(['uh oh', 'uh oh']);
   });
+
+  // @gate enablePostpone
+  it('supports postponing in prerender and resuming later', async () => {
+    let prerendering = true;
+    function Postpone() {
+      if (prerendering) {
+        React.unstable_postpone();
+      }
+      return 'Hello';
+    }
+
+    function App() {
+      return (
+        <div>
+          <Suspense fallback="Loading...">
+            <Postpone />
+          </Suspense>
+        </div>
+      );
+    }
+
+    const prerendered = await ReactDOMFizzStatic.prerender(<App />);
+    expect(prerendered.postponed).not.toBe(null);
+
+    prerendering = false;
+
+    const resumed = await ReactDOMFizzServer.resume(
+      <App />,
+      prerendered.postponed,
+    );
+
+    await readIntoContainer(prerendered.prelude);
+
+    expect(getVisibleChildren(container)).toEqual(<div>Loading...</div>);
+
+    await readIntoContainer(resumed);
+
+    // TODO: expect(getVisibleChildren(container)).toEqual(<div>Hello</div>);
+  });
+
+  // @gate enablePostpone
+  it('only emits end tags once when resuming', async () => {
+    let prerendering = true;
+    function Postpone() {
+      if (prerendering) {
+        React.unstable_postpone();
+      }
+      return 'Hello';
+    }
+
+    function App() {
+      return (
+        <html>
+          <body>
+            <Suspense fallback="Loading...">
+              <Postpone />
+            </Suspense>
+          </body>
+        </html>
+      );
+    }
+
+    const prerendered = await ReactDOMFizzStatic.prerender(<App />);
+    expect(prerendered.postponed).not.toBe(null);
+
+    prerendering = false;
+
+    const content = await ReactDOMFizzServer.resume(
+      <App />,
+      prerendered.postponed,
+    );
+
+    const html = await readContent(concat(prerendered.prelude, content));
+    const htmlEndTags = /<\/html\s*>/gi;
+    const bodyEndTags = /<\/body\s*>/gi;
+    expect(Array.from(html.matchAll(htmlEndTags)).length).toBe(1);
+    expect(Array.from(html.matchAll(bodyEndTags)).length).toBe(1);
+  });
 });

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

@@ -16,7 +16,7 @@ import ReactVersion from 'shared/ReactVersion';
 
 import {
   createRequest,
-  startWork,
+  startRender,
   startFlowing,
   abort,
 } from 'react-server/src/ReactFizzServer';
@@ -129,7 +129,7 @@ function renderToReadableStream(
         signal.addEventListener('abort', listener);
       }
     }
-    startWork(request);
+    startRender(request);
   });
 }
 
@@ -200,7 +200,7 @@ function resume(
         signal.addEventListener('abort', listener);
       }
     }
-    startWork(request);
+    startRender(request);
   });
 }
 

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

@@ -15,7 +15,7 @@ import ReactVersion from 'shared/ReactVersion';
 
 import {
   createRequest,
-  startWork,
+  startRender,
   startFlowing,
   abort,
 } from 'react-server/src/ReactFizzServer';
@@ -121,7 +121,7 @@ function renderToReadableStream(
         signal.addEventListener('abort', listener);
       }
     }
-    startWork(request);
+    startRender(request);
   });
 }