Make ART Concurrent if Legacy Mode is disabled (#28662)

Pulling this out of #28657.

This runs react-art in concurrent mode if disableLegacyMode is true.
Effectively this means that the OSS version will be in concurrent mode
and the `.modern.js` version for Meta will be in concurrent mode, once
the flag flips for modern, but the `.classic.js` version for Meta will
be in legacy mode.

Updates flowing in from above flush synchronously so that they commit as
a unit. This also ensures that refs are resolved before the parent life
cycles. setStates deep in the tree will now be batched using "discrete"
priority but should still happen same task.

packages/react-art/src/ReactART.js

@@ -7,15 +7,17 @@
 
 import * as React from 'react';
 import ReactVersion from 'shared/ReactVersion';
-import {LegacyRoot} from 'react-reconciler/src/ReactRootTags';
+import {LegacyRoot, ConcurrentRoot} from 'react-reconciler/src/ReactRootTags';
 import {
   createContainer,
   updateContainer,
   injectIntoDevTools,
+  flushSync,
 } from 'react-reconciler/src/ReactFiberReconciler';
 import Transform from 'art/core/transform';
 import Mode from 'art/modes/current';
 import FastNoSideEffects from 'art/modes/fast-noSideEffects';
+import {disableLegacyMode} from 'shared/ReactFeatureFlags';
 
 import {TYPES, childrenAsString} from './ReactARTInternals';
 
@@ -68,13 +70,17 @@ class Surface extends React.Component {
 
     this._mountNode = createContainer(
       this._surface,
-      LegacyRoot,
+      disableLegacyMode ? ConcurrentRoot : LegacyRoot,
       null,
       false,
       false,
       '',
     );
-    updateContainer(this.props.children, this._mountNode, this);
+    // We synchronously flush updates coming from above so that they commit together
+    // and so that refs resolve before the parent life cycles.
+    flushSync(() => {
+      updateContainer(this.props.children, this._mountNode, this);
+    });
   }
 
   componentDidUpdate(prevProps, prevState) {
@@ -84,15 +90,23 @@ class Surface extends React.Component {
       this._surface.resize(+props.width, +props.height);
     }
 
-    updateContainer(this.props.children, this._mountNode, this);
+    // We synchronously flush updates coming from above so that they commit together
+    // and so that refs resolve before the parent life cycles.
+    flushSync(() => {
+      updateContainer(this.props.children, this._mountNode, this);
+    });
 
     if (this._surface.render) {
       this._surface.render();
     }
   }
 
   componentWillUnmount() {
-    updateContainer(null, this._mountNode, this);
+    // We synchronously flush updates coming from above so that they commit together
+    // and so that refs resolve before the parent life cycles.
+    flushSync(() => {
+      updateContainer(null, this._mountNode, this);
+    });
   }
 
   render() {

packages/react-art/src/__tests__/ReactART-test.js

@@ -11,7 +11,8 @@
 
 'use strict';
 
-import * as React from 'react';
+const React = require('react');
+const Scheduler = require('scheduler');
 
 import * as ReactART from 'react-art';
 import ARTSVGMode from 'art/modes/svg';
@@ -22,22 +23,28 @@ import Circle from 'react-art/Circle';
 import Rectangle from 'react-art/Rectangle';
 import Wedge from 'react-art/Wedge';
 
+const {act, waitFor} = require('internal-test-utils');
+
 // Isolate DOM renderer.
 jest.resetModules();
+// share isomorphic
+jest.mock('scheduler', () => Scheduler);
+jest.mock('react', () => React);
+const ReactDOM = require('react-dom');
 const ReactDOMClient = require('react-dom/client');
-let act = require('internal-test-utils').act;
 
 // Isolate the noop renderer
 jest.resetModules();
+// share isomorphic
+jest.mock('scheduler', () => Scheduler);
+jest.mock('react', () => React);
 const ReactNoop = require('react-noop-renderer');
-const Scheduler = require('scheduler');
 
 let Group;
 let Shape;
 let Surface;
 let TestComponent;
 
-let waitFor;
 let groupRef;
 
 const Missing = {};
@@ -68,6 +75,11 @@ describe('ReactART', () => {
   let container;
 
   beforeEach(() => {
+    jest.resetModules();
+    // share isomorphic
+    jest.mock('scheduler', () => Scheduler);
+    jest.mock('react', () => React);
+
     container = document.createElement('div');
     document.body.appendChild(container);
 
@@ -77,8 +89,6 @@ describe('ReactART', () => {
     Shape = ReactART.Shape;
     Surface = ReactART.Surface;
 
-    ({waitFor} = require('internal-test-utils'));
-
     groupRef = React.createRef();
     TestComponent = class extends React.Component {
       group = groupRef;
@@ -409,8 +419,6 @@ describe('ReactART', () => {
       );
     }
 
-    // Using test renderer instead of the DOM renderer here because async
-    // testing APIs for the DOM renderer don't exist.
     ReactNoop.render(
       <CurrentRendererContext.Provider value="Test">
         <Yield value="A" />
@@ -423,7 +431,9 @@ describe('ReactART', () => {
     await waitFor(['A']);
 
     const root = ReactDOMClient.createRoot(container);
-    await act(() => {
+    // We use flush sync here because we expect this to render in between
+    // while the concurrent render is yieldy where as act would flush both.
+    ReactDOM.flushSync(() => {
       root.render(
         <Surface>
           <LogCurrentRenderer />
@@ -434,8 +444,6 @@ describe('ReactART', () => {
       );
     });
 
-    expect(ops).toEqual([null, 'ART']);
-
     ops = [];
     await waitFor(['B', 'C']);
 
@@ -447,9 +455,11 @@ describe('ReactARTComponents', () => {
   let ReactTestRenderer;
   beforeEach(() => {
     jest.resetModules();
+    // share isomorphic
+    jest.mock('scheduler', () => Scheduler);
+    jest.mock('react', () => React);
     // Isolate test renderer.
     ReactTestRenderer = require('react-test-renderer');
-    act = require('internal-test-utils').act;
   });
 
   it('should generate a <Shape> with props for drawing the Circle', async () => {