Revert "Revert "Cleanup enableSyncDefaultUpdate flag (#26236)" (#26528)"

This reverts commit da94e8b.

Author: kassens

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

@@ -33,16 +33,12 @@ const ReactTestRenderer = require('react-test-renderer');
 
 // Isolate the noop renderer
 jest.resetModules();
-const ReactNoop = require('react-noop-renderer');
-const Scheduler = require('scheduler');
 
 let Group;
 let Shape;
 let Surface;
 let TestComponent;
 
-let waitFor;
-
 const Missing = {};
 
 function testDOMNodeStructure(domNode, expectedStructure) {
@@ -80,8 +76,6 @@ describe('ReactART', () => {
     Shape = ReactART.Shape;
     Surface = ReactART.Surface;
 
-    ({waitFor} = require('internal-test-utils'));
-
     TestComponent = class extends React.Component {
       group = React.createRef();
 
@@ -363,58 +357,6 @@ describe('ReactART', () => {
     doClick(instance);
     expect(onClick2).toBeCalled();
   });
-
-  // @gate !enableSyncDefaultUpdates
-  it('can concurrently render with a "primary" renderer while sharing context', async () => {
-    const CurrentRendererContext = React.createContext(null);
-
-    function Yield(props) {
-      Scheduler.log(props.value);
-      return null;
-    }
-
-    let ops = [];
-    function LogCurrentRenderer() {
-      return (
-        <CurrentRendererContext.Consumer>
-          {currentRenderer => {
-            ops.push(currentRenderer);
-            return null;
-          }}
-        </CurrentRendererContext.Consumer>
-      );
-    }
-
-    // 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" />
-        <Yield value="B" />
-        <LogCurrentRenderer />
-        <Yield value="C" />
-      </CurrentRendererContext.Provider>,
-    );
-
-    await waitFor(['A']);
-
-    ReactDOM.render(
-      <Surface>
-        <LogCurrentRenderer />
-        <CurrentRendererContext.Provider value="ART">
-          <LogCurrentRenderer />
-        </CurrentRendererContext.Provider>
-      </Surface>,
-      container,
-    );
-
-    expect(ops).toEqual([null, 'ART']);
-
-    ops = [];
-    await waitFor(['B', 'C']);
-
-    expect(ops).toEqual(['Test']);
-  });
 });
 
 describe('ReactARTComponents', () => {

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

@@ -312,11 +312,7 @@ describe('ReactDOMNativeEventHeuristic-test', () => {
       expect(container.textContent).toEqual('not hovered');
 
       await waitFor(['hovered']);
-      if (gate(flags => flags.enableSyncDefaultUpdates)) {
-        expect(container.textContent).toEqual('hovered');
-      } else {
-        expect(container.textContent).toEqual('not hovered');
-      }
+      expect(container.textContent).toEqual('hovered');
     });
     expect(container.textContent).toEqual('hovered');
   });

packages/react-dom/src/__tests__/ReactDOMServerPartialHydration-test.internal.js

@@ -2036,14 +2036,7 @@ describe('ReactDOMServerPartialHydration', () => {
     suspend = true;
 
     await act(async () => {
-      if (gate(flags => flags.enableSyncDefaultUpdates)) {
-        await waitFor(['Before', 'After']);
-      } else {
-        await waitFor(['Before']);
-        // This took a long time to render.
-        Scheduler.unstable_advanceTime(1000);
-        await waitFor(['After']);
-      }
+      await waitFor(['Before', 'After']);
 
       // This will cause us to skip the second row completely.
     });

packages/react-dom/src/events/__tests__/DOMPluginEventSystem-test.internal.js

@@ -1984,13 +1984,9 @@ describe('DOMPluginEventSystem', () => {
             log.length = 0;
 
             // Increase counter
-            if (gate(flags => flags.enableSyncDefaultUpdates)) {
-              React.startTransition(() => {
-                root.render(<Test counter={1} />);
-              });
-            } else {
+            React.startTransition(() => {
               root.render(<Test counter={1} />);
-            }
+            });
             // Yield before committing
             await waitFor(['Test']);
 

packages/react-reconciler/src/ReactFiber.js

@@ -33,7 +33,6 @@ import {
   enableProfilerTimer,
   enableScopeAPI,
   enableLegacyHidden,
-  enableSyncDefaultUpdates,
   allowConcurrentByDefault,
   enableTransitionTracing,
   enableDebugTracing,
@@ -459,11 +458,9 @@ export function createHostRootFiber(
       mode |= StrictLegacyMode | StrictEffectsMode;
     }
     if (
-      // We only use this flag for our repo tests to check both behaviors.
-      // TODO: Flip this flag and rename it something like "forceConcurrentByDefaultForTesting"
-      !enableSyncDefaultUpdates ||
       // Only for internal experiments.
-      (allowConcurrentByDefault && concurrentUpdatesByDefaultOverride)
+      allowConcurrentByDefault &&
+      concurrentUpdatesByDefaultOverride
     ) {
       mode |= ConcurrentUpdatesByDefaultMode;
     }