Get legacy ReactCurrentActQueue checks

Author: sebmarkbage

packages/react/src/ReactAct.js

@@ -12,6 +12,8 @@ import type {RendererTask} from './ReactCurrentActQueue';
 import ReactCurrentActQueue from './ReactCurrentActQueue';
 import queueMacrotask from 'shared/enqueueTask';
 
+import {disableLegacyMode} from 'shared/ReactFeatureFlags';
+
 // `act` calls can be nested, so we track the depth. This represents the
 // number of `act` scopes on the stack.
 let actScopeDepth = 0;
@@ -38,7 +40,9 @@ export function act<T>(callback: () => T | Thenable<T>): Thenable<T> {
     // `act` calls can be nested.
     //
     // If we're already inside an `act` scope, reuse the existing queue.
-    const prevIsBatchingLegacy = ReactCurrentActQueue.isBatchingLegacy;
+    const prevIsBatchingLegacy = !disableLegacyMode
+      ? ReactCurrentActQueue.isBatchingLegacy
+      : false;
     const prevActQueue = ReactCurrentActQueue.current;
     const prevActScopeDepth = actScopeDepth;
     actScopeDepth++;
@@ -48,7 +52,9 @@ export function act<T>(callback: () => T | Thenable<T>): Thenable<T> {
     // set to `true` while the given callback is executed, not for updates
     // triggered during an async event, because this is how the legacy
     // implementation of `act` behaved.
-    ReactCurrentActQueue.isBatchingLegacy = true;
+    if (!disableLegacyMode) {
+      ReactCurrentActQueue.isBatchingLegacy = true;
+    }
 
     let result;
     // This tracks whether the `act` call is awaited. In certain cases, not
@@ -58,10 +64,13 @@ export function act<T>(callback: () => T | Thenable<T>): Thenable<T> {
       // Reset this to `false` right before entering the React work loop. The
       // only place we ever read this fields is just below, right after running
       // the callback. So we don't need to reset after the callback runs.
-      ReactCurrentActQueue.didScheduleLegacyUpdate = false;
+      if (!disableLegacyMode) {
+        ReactCurrentActQueue.didScheduleLegacyUpdate = false;
+      }
       result = callback();
-      const didScheduleLegacyUpdate =
-        ReactCurrentActQueue.didScheduleLegacyUpdate;
+      const didScheduleLegacyUpdate = !disableLegacyMode
+        ? ReactCurrentActQueue.didScheduleLegacyUpdate
+        : false;
 
       // Replicate behavior of original `act` implementation in legacy mode,
       // which flushed updates immediately after the scope function exits, even
@@ -73,7 +82,9 @@ export function act<T>(callback: () => T | Thenable<T>): Thenable<T> {
       // one used to track `act` scopes. Why, you may be wondering? Because
       // that's how it worked before version 18. Yes, it's confusing! We should
       // delete legacy mode!!
-      ReactCurrentActQueue.isBatchingLegacy = prevIsBatchingLegacy;
+      if (!disableLegacyMode) {
+        ReactCurrentActQueue.isBatchingLegacy = prevIsBatchingLegacy;
+      }
     } catch (error) {
       // `isBatchingLegacy` gets reset using the regular stack, not the async
       // one used to track `act` scopes. Why, you may be wondering? Because
@@ -82,7 +93,9 @@ export function act<T>(callback: () => T | Thenable<T>): Thenable<T> {
       ReactCurrentActQueue.thrownErrors.push(error);
     }
     if (ReactCurrentActQueue.thrownErrors.length > 0) {
-      ReactCurrentActQueue.isBatchingLegacy = prevIsBatchingLegacy;
+      if (!disableLegacyMode) {
+        ReactCurrentActQueue.isBatchingLegacy = prevIsBatchingLegacy;
+      }
       popActScope(prevActQueue, prevActScopeDepth);
       const thrownError = aggregateErrors(ReactCurrentActQueue.thrownErrors);
       ReactCurrentActQueue.thrownErrors.length = 0;