[FB] disable legacy mode in modern build

Disables legacy mode in www-modern and removes the entrypoint hack in tests since we gate legacy mode tests now

Additionally disables test utils because this relies on legacy mode.

Additionally gates react-test-renderer test for unstable_Scope because it seems to also rely on legacy roots.

Author: gnoff

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

@@ -47,7 +47,7 @@ describe('ReactDOMRoot', () => {
     expect(container.textContent).toEqual('Hi');
   });
 
-  // @gate !classic || !__DEV__
+  // @gate !disableLegacyMode
   it('warns if you import createRoot from react-dom', async () => {
     expect(() => ReactDOM.createRoot(container)).toErrorDev(
       'You are importing createRoot from "react-dom" which is not supported. ' +
@@ -58,7 +58,7 @@ describe('ReactDOMRoot', () => {
     );
   });
 
-  // @gate !classic || !__DEV__
+  // @gate !disableLegacyMode
   it('warns if you import hydrateRoot from react-dom', async () => {
     expect(() => ReactDOM.hydrateRoot(container, null)).toErrorDev(
       'You are importing hydrateRoot from "react-dom" which is not supported. ' +

packages/react-reconciler/src/__tests__/ReactScope-test.internal.js

@@ -393,6 +393,7 @@ describe('ReactScope', () => {
     });
 
     // @gate www
+    // @gate !disableLegacyMode
     it('DO_NOT_USE_queryAllNodes() works as intended', () => {
       const testScopeQuery = (type, props) => true;
       const TestScope = React.unstable_Scope;
@@ -430,6 +431,7 @@ describe('ReactScope', () => {
     });
 
     // @gate www
+    // @gate !disableLegacyMode
     it('DO_NOT_USE_queryFirstNode() works as intended', () => {
       const testScopeQuery = (type, props) => true;
       const TestScope = React.unstable_Scope;
@@ -467,6 +469,7 @@ describe('ReactScope', () => {
     });
 
     // @gate www
+    // @gate !disableLegacyMode
     it('containsNode() works as intended', () => {
       const TestScope = React.unstable_Scope;
       const scopeRef = React.createRef();

packages/react-reconciler/src/__tests__/ReactSuspense-test.internal.js

@@ -379,6 +379,7 @@ describe('ReactSuspense', () => {
   });
 
   // @gate forceConcurrentByDefaultForTesting
+  // @gate !disableLegacyMode
   it(
     'interrupts current render when something suspends with a ' +
       "delay and we've already skipped over a lower priority update in " +

packages/shared/forks/ReactFeatureFlags.www.js

@@ -114,9 +114,10 @@ export const useModernStrictMode = true;
 // because JSX is an extremely hot path.
 export const disableStringRefs = false;
 
-export const disableLegacyMode = false;
-
-export const disableDOMTestUtils = false;
+// These flags need to be on together because disabled legacy mode breaks test utils
+// since it is written on top of legacy mode
+export const disableLegacyMode = __EXPERIMENTAL__;
+export const disableDOMTestUtils = __EXPERIMENTAL__;
 
 // Flow magic to verify the exports of this file match the original version.
 ((((null: any): ExportsType): FeatureFlagsType): ExportsType);

scripts/jest/setupHostConfigs.js

@@ -14,11 +14,6 @@ function resolveEntryFork(resolvedEntry, isFBBundle) {
   // .js
 
   if (isFBBundle) {
-    if (__EXPERIMENTAL__) {
-      // We can't currently use the true modern entry point because too many tests fail.
-      // TODO: Fix tests to not use ReactDOM.render or gate them. Then we can remove this.
-      return resolvedEntry;
-    }
     const resolvedFBEntry = resolvedEntry.replace(
       '.js',
       __EXPERIMENTAL__ ? '.modern.fb.js' : '.classic.fb.js'