Ensure createRoot warning parity with ReactDOM.render

Author: trueadm

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

@@ -258,4 +258,34 @@ describe('ReactDOMRoot', () => {
     Scheduler.unstable_flushAll();
     ReactDOM.createRoot(container); // No warning
   });
+
+  it('warns if creating a root on the document.body', async () => {
+    expect(() => {
+      ReactDOM.createRoot(document.body);
+    }).toErrorDev(
+      'createRoot(): Creating roots directly with document.body is ' +
+        'discouraged, since its children are often manipulated by third-party ' +
+        'scripts and browser extensions. This may lead to subtle ' +
+        'reconciliation issues. Try using a container element created ' +
+        'for your app.',
+      {withoutStack: true},
+    );
+  });
+
+  it('warns if updating a root that has had its contents removed', async () => {
+    const root = ReactDOM.createRoot(container);
+    root.render(<div>Hi</div>);
+    Scheduler.unstable_flushAll();
+    container.innerHTML = '';
+
+    expect(() => {
+      root.render(<div>Hi</div>);
+    }).toErrorDev(
+      'render(...): It looks like the React-rendered content of the ' +
+        'root container was removed without using React. This is not ' +
+        'supported and will cause errors. Instead, call ' +
+        "root.unmount() to empty a root's container.",
+      {withoutStack: true},
+    );
+  });
 });

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

@@ -13,6 +13,7 @@ import type {ReactNodeList} from 'shared/ReactTypes';
 // TODO: This type is shared between the reconciler and ReactDOM, but will
 // eventually be lifted out to the renderer.
 import type {FiberRoot} from 'react-reconciler/src/ReactFiberRoot';
+import {findHostInstanceWithNoPortals} from 'react-reconciler/inline.dom';
 
 export type RootType = {
   render(children: ReactNodeList): void,
@@ -63,15 +64,30 @@ function ReactDOMBlockingRoot(
 ReactDOMRoot.prototype.render = ReactDOMBlockingRoot.prototype.render = function(
   children: ReactNodeList,
 ): void {
+  const root = this._internalRoot;
   if (__DEV__) {
     if (typeof arguments[1] === 'function') {
       console.error(
         'render(...): does not support the second callback argument. ' +
           'To execute a side effect after rendering, declare it in a component body with useEffect().',
       );
     }
+    const container = root.containerInfo;
+
+    if (container.nodeType !== COMMENT_NODE) {
+      const hostInstance = findHostInstanceWithNoPortals(root.current);
+      if (hostInstance) {
+        if (hostInstance.parentNode !== container) {
+          console.error(
+            'render(...): It looks like the React-rendered content of the ' +
+              'root container was removed without using React. This is not ' +
+              'supported and will cause errors. Instead, call ' +
+              "root.unmount() to empty a root's container.",
+          );
+        }
+      }
+    }
   }
-  const root = this._internalRoot;
   updateContainer(children, root, null, null);
 };
 
@@ -96,6 +112,21 @@ function createRootImpl(
   tag: RootTag,
   options: void | RootOptions,
 ) {
+  if (__DEV__) {
+    if (
+      container.nodeType === ELEMENT_NODE &&
+      ((container: any): Element).tagName &&
+      ((container: any): Element).tagName.toUpperCase() === 'BODY'
+    ) {
+      console.error(
+        'createRoot(): Creating roots directly with document.body is ' +
+          'discouraged, since its children are often manipulated by third-party ' +
+          'scripts and browser extensions. This may lead to subtle ' +
+          'reconciliation issues. Try using a container element created ' +
+          'for your app.',
+      );
+    }
+  }
   // Tag is either LegacyRoot or Concurrent Root
   const hydrate = options != null && options.hydrate === true;
   const hydrationCallbacks =