Allow Float methods to be called anytime in Fiber

Previously we restricted Float methods to only being callable while rendering. This allowed us to make associations between calls and their position in the DOM tree, for instance hoisting preinitialized styles into a ShadowRoot or an iframe Document.

When considering how we are going to support Flight support in Float however it became clear that this restriction would lead to compromises on the implementation because the Flight client does not execute within the context of a client render. We want to be able to disaptch Float directives coming from Flight as soon as possible and this requires being able to call them outside of render.

this patch modifies Float so that its methods are callable anywhere. The main consequence of this change is Float will always use the Document the renderer script is running within as the HoistableRoot. This means if you preinit as style inside a component render targeting a ShadowRoot the style will load in the ownerDocument not the ShadowRoot. Practially speaking it means that preinit is not useful inside ShadowRoots and iframes.

This tradeoff was deemed acceptable because these methods are optimistic, not critical. Additionally, the other methods, preconntect, prefetchDNS, and preload, are not impacted because they already operated at the level of the ownerDocument and really only interface with the Network cache layer.

Author: gnoff

packages/react-dom-bindings/src/client/ReactDOMHostConfig.js

@@ -25,8 +25,6 @@ import {ConcurrentMode, NoMode} from 'react-reconciler/src/ReactTypeOfMode';
 
 import hasOwnProperty from 'shared/hasOwnProperty';
 import {checkAttributeStringCoercion} from 'shared/CheckStringCoercion';
-import ReactDOMSharedInternals from 'shared/ReactDOMSharedInternals.js';
-const {Dispatcher} = ReactDOMSharedInternals;
 
 import {
   precacheFiberNode,
@@ -1939,24 +1937,9 @@ export function prepareToCommitHoistables() {
 // that the resource is meant to apply too (for example stylesheets or scripts). This is only
 // appropriate for resources that don't really have a strict tie to the document itself for example
 // preloads
-let lastCurrentDocument: ?Document = null;
-let previousDispatcher = null;
-export function prepareRendererToRender(rootContainer: Container) {
-  if (enableFloat) {
-    const rootNode = getHoistableRoot(rootContainer);
-    lastCurrentDocument = getDocumentFromRoot(rootNode);
-
-    previousDispatcher = Dispatcher.current;
-    Dispatcher.current = ReactDOMClientDispatcher;
-  }
-}
+export function prepareRendererToRender(rootContainer: Container) {}
 
-export function resetRendererAfterRender() {
-  if (enableFloat) {
-    Dispatcher.current = previousDispatcher;
-    previousDispatcher = null;
-  }
-}
+export function resetRendererAfterRender() {}
 
 // global collections of Resources
 const preloadPropsMap: Map<string, PreloadProps> = new Map();
@@ -1979,25 +1962,6 @@ function getCurrentResourceRoot(): null | HoistableRoot {
   return currentContainer ? getHoistableRoot(currentContainer) : null;
 }
 
-// Preloads are somewhat special. Even if we don't have the Document
-// used by the root that is rendering a component trying to insert a preload
-// we can still seed the file cache by doing the preload on any document we have
-// access to. We prefer the currentDocument if it exists, we also prefer the
-// lastCurrentDocument if that exists. As a fallback we will use the window.document
-// if available.
-function getDocumentForPreloads(): ?Document {
-  const root = getCurrentResourceRoot();
-  if (root) {
-    return root.ownerDocument || root;
-  } else {
-    try {
-      return lastCurrentDocument || window.document;
-    } catch (error) {
-      return null;
-    }
-  }
-}
-
 function getDocumentFromRoot(root: HoistableRoot): Document {
   return root.ownerDocument || root;
 }
@@ -2012,13 +1976,23 @@ export const ReactDOMClientDispatcher = {
   preinit,
 };
 
+// We expect this to get inlined. It is a function mostly to communicate the special nature of
+// how we resolve the HoistableRoot for ReactDOM.pre*() methods. Because we support calling
+// these methods outside of render there is no way to know which Document or ShadowRoot is 'scoped'
+// and so we have to fall back to something universal. Currently we just refer to the global document.
+// This is notable because nowhere else in ReactDOM do we actually reference the global document or window
+// because we may be rendering inside an iframe.
+function getDocumentForImperativeFloatMethods(): Document {
+  return document;
+}
+
 function preconnectAs(
   rel: 'preconnect' | 'dns-prefetch',
   crossOrigin: null | '' | 'use-credentials',
   href: string,
 ) {
-  const ownerDocument = getDocumentForPreloads();
-  if (typeof href === 'string' && href && ownerDocument) {
+  const ownerDocument = getDocumentForImperativeFloatMethods();
+  if (typeof href === 'string' && href) {
     const limitedEscapedHref =
       escapeSelectorAttributeValueInsideDoubleQuotes(href);
     let key = `link[rel="${rel}"][href="${limitedEscapedHref}"]`;
@@ -2040,6 +2014,9 @@ function preconnectAs(
 }
 
 function prefetchDNS(href: string, options?: mixed) {
+  if (!enableFloat) {
+    return;
+  }
   if (__DEV__) {
     if (typeof href !== 'string' || !href) {
       console.error(
@@ -2067,6 +2044,9 @@ function prefetchDNS(href: string, options?: mixed) {
 }
 
 function preconnect(href: string, options?: {crossOrigin?: string}) {
+  if (!enableFloat) {
+    return;
+  }
   if (__DEV__) {
     if (typeof href !== 'string' || !href) {
       console.error(
@@ -2102,10 +2082,13 @@ type PreloadOptions = {
   type?: string,
 };
 function preload(href: string, options: PreloadOptions) {
+  if (!enableFloat) {
+    return;
+  }
   if (__DEV__) {
     validatePreloadArguments(href, options);
   }
-  const ownerDocument = getDocumentForPreloads();
+  const ownerDocument = getDocumentForImperativeFloatMethods();
   if (
     typeof href === 'string' &&
     href &&
@@ -2163,61 +2146,25 @@ type PreinitOptions = {
   integrity?: string,
 };
 function preinit(href: string, options: PreinitOptions) {
+  if (!enableFloat) {
+    return;
+  }
   if (__DEV__) {
     validatePreinitArguments(href, options);
   }
+  const ownerDocument = getDocumentForImperativeFloatMethods();
 
   if (
     typeof href === 'string' &&
     href &&
     typeof options === 'object' &&
     options !== null
   ) {
-    const resourceRoot = getCurrentResourceRoot();
     const as = options.as;
-    if (!resourceRoot) {
-      if (as === 'style' || as === 'script') {
-        // We are going to emit a preload as a best effort fallback since this preinit
-        // was called outside of a render. Given the passive nature of this fallback
-        // we do not warn in dev when props disagree if there happens to already be a
-        // matching preload with this href
-        const preloadDocument = getDocumentForPreloads();
-        if (preloadDocument) {
-          const limitedEscapedHref =
-            escapeSelectorAttributeValueInsideDoubleQuotes(href);
-          const preloadKey = `link[rel="preload"][as="${as}"][href="${limitedEscapedHref}"]`;
-          let key = preloadKey;
-          switch (as) {
-            case 'style':
-              key = getStyleKey(href);
-              break;
-            case 'script':
-              key = getScriptKey(href);
-              break;
-          }
-          if (!preloadPropsMap.has(key)) {
-            const preloadProps = preloadPropsFromPreinitOptions(
-              href,
-              as,
-              options,
-            );
-            preloadPropsMap.set(key, preloadProps);
-
-            if (null === preloadDocument.querySelector(preloadKey)) {
-              const instance = preloadDocument.createElement('link');
-              setInitialProperties(instance, 'link', preloadProps);
-              markNodeAsHoistable(instance);
-              (preloadDocument.head: any).appendChild(instance);
-            }
-          }
-        }
-      }
-      return;
-    }
 
     switch (as) {
       case 'style': {
-        const styles = getResourcesFromRoot(resourceRoot).hoistableStyles;
+        const styles = getResourcesFromRoot(ownerDocument).hoistableStyles;
 
         const key = getStyleKey(href);
         const precedence = options.precedence || 'default';
@@ -2236,7 +2183,7 @@ function preinit(href: string, options: PreinitOptions) {
         };
 
         // Attempt to hydrate instance from DOM
-        let instance: null | Instance = resourceRoot.querySelector(
+        let instance: null | Instance = ownerDocument.querySelector(
           getStylesheetSelectorFromKey(key),
         );
         if (instance) {
@@ -2252,7 +2199,6 @@ function preinit(href: string, options: PreinitOptions) {
           if (preloadProps) {
             adoptPreloadPropsForStylesheet(stylesheetProps, preloadProps);
           }
-          const ownerDocument = getDocumentFromRoot(resourceRoot);
           const link = (instance = ownerDocument.createElement('link'));
           markNodeAsHoistable(link);
           setInitialProperties(link, 'link', stylesheetProps);
@@ -2269,7 +2215,7 @@ function preinit(href: string, options: PreinitOptions) {
           });
 
           state.loading |= Inserted;
-          insertStylesheet(instance, precedence, resourceRoot);
+          insertStylesheet(instance, precedence, ownerDocument);
         }
 
         // Construct a Resource and cache it
@@ -2284,7 +2230,7 @@ function preinit(href: string, options: PreinitOptions) {
       }
       case 'script': {
         const src = href;
-        const scripts = getResourcesFromRoot(resourceRoot).hoistableScripts;
+        const scripts = getResourcesFromRoot(ownerDocument).hoistableScripts;
 
         const key = getScriptKey(src);
 
@@ -2297,7 +2243,7 @@ function preinit(href: string, options: PreinitOptions) {
         }
 
         // Attempt to hydrate instance from DOM
-        let instance: null | Instance = resourceRoot.querySelector(
+        let instance: null | Instance = ownerDocument.querySelector(
           getScriptSelectorFromKey(key),
         );
         if (!instance) {
@@ -2308,7 +2254,6 @@ function preinit(href: string, options: PreinitOptions) {
           if (preloadProps) {
             adoptPreloadPropsForScript(scriptProps, preloadProps);
           }
-          const ownerDocument = getDocumentFromRoot(resourceRoot);
           instance = ownerDocument.createElement('script');
           markNodeAsHoistable(instance);
           setInitialProperties(instance, 'link', scriptProps);
@@ -2329,20 +2274,6 @@ function preinit(href: string, options: PreinitOptions) {
   }
 }
 
-function preloadPropsFromPreinitOptions(
-  href: string,
-  as: ResourceType,
-  options: PreinitOptions,
-): PreloadProps {
-  return {
-    href,
-    rel: 'preload',
-    as,
-    crossOrigin: as === 'font' ? '' : options.crossOrigin,
-    integrity: options.integrity,
-  };
-}
-
 function stylesheetPropsFromPreinitOptions(
   href: string,
   precedence: string,

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

@@ -24,8 +24,6 @@ let ReactDOMFizzServer;
 let Suspense;
 let textCache;
 let loadCache;
-let window;
-let document;
 let writable;
 const CSPnonce = null;
 let container;
@@ -51,8 +49,8 @@ function resetJSDOM(markup) {
       media: query,
     })),
   });
-  window = jsdom.window;
-  document = jsdom.window.document;
+  global.window = jsdom.window;
+  global.document = jsdom.window.document;
 }
 
 describe('ReactDOMFloat', () => {
@@ -3750,7 +3748,7 @@ body {
     });
 
     // @gate enableFloat
-    it('creates a preload resource when ReactDOM.preinit(..., {as: "style" }) is called outside of render on the client', async () => {
+    it('creates a stylesheet resource in the ownerDocument when ReactDOM.preinit(..., {as: "style" }) is called outside of render on the client', async () => {
       function App() {
         React.useEffect(() => {
           ReactDOM.preinit('foo', {as: 'style'});
@@ -3768,11 +3766,55 @@ body {
       expect(getMeaningfulChildren(document)).toEqual(
         <html>
           <head>
-            <link rel="preload" href="foo" as="style" />
+            <link rel="stylesheet" href="foo" data-precedence="default" />
+          </head>
+          <body>foo</body>
+        </html>,
+      );
+    });
+
+    // @gate enableFloat
+    it('creates a stylesheet resource in the ownerDocument when ReactDOM.preinit(..., {as: "style" }) is called outside of render on the client', async () => {
+      // This is testing behavior, but it shows that it is not a good idea to preinit inside a shadowRoot. The point is we are asserting a behavior
+      // you would want to avoid in a real app.
+      const shadow = document.body.attachShadow({mode: 'open'});
+      function ShadowComponent() {
+        ReactDOM.preinit('bar', {as: 'style'});
+        return null;
+      }
+      function App() {
+        React.useEffect(() => {
+          ReactDOM.preinit('foo', {as: 'style'});
+        }, []);
+        return (
+          <html>
+            <body>
+              foo
+              {ReactDOM.createPortal(
+                <div>
+                  <ShadowComponent />
+                  shadow
+                </div>,
+                shadow,
+              )}
+            </body>
+          </html>
+        );
+      }
+
+      const root = ReactDOMClient.createRoot(document);
+      root.render(<App />);
+      await waitForAll([]);
+      expect(getMeaningfulChildren(document)).toEqual(
+        <html>
+          <head>
+            <link rel="stylesheet" href="bar" data-precedence="default" />
+            <link rel="stylesheet" href="foo" data-precedence="default" />
           </head>
           <body>foo</body>
         </html>,
       );
+      expect(getMeaningfulChildren(shadow)).toEqual(<div>shadow</div>);
     });
 
     // @gate enableFloat
@@ -3872,7 +3914,7 @@ body {
       expect(getMeaningfulChildren(document)).toEqual(
         <html>
           <head>
-            <link rel="preload" href="foo" as="script" />
+            <script async="" src="foo" />
           </head>
           <body>foo</body>
         </html>,

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

@@ -247,11 +247,8 @@ export function createRoot(
     transitionCallbacks,
   );
   markContainerAsRoot(root.current, container);
+  Dispatcher.current = ReactDOMClientDispatcher;
 
-  if (enableFloat) {
-    // Set the default dispatcher to the client dispatcher
-    Dispatcher.current = ReactDOMClientDispatcher;
-  }
   const rootContainerElement: Document | Element | DocumentFragment =
     container.nodeType === COMMENT_NODE
       ? (container.parentNode: any)
@@ -339,10 +336,7 @@ export function hydrateRoot(
     transitionCallbacks,
   );
   markContainerAsRoot(root.current, container);
-  if (enableFloat) {
-    // Set the default dispatcher to the client dispatcher
-    Dispatcher.current = ReactDOMClientDispatcher;
-  }
+  Dispatcher.current = ReactDOMClientDispatcher;
   // This can't be a comment node since hydration doesn't work on comment nodes anyway.
   listenToAllSupportedEvents(container);