www: make disableLegacyMode dynamic flag (#29774)

This makes the flag dynamic for Meta and turns it on for the www test
renderer.

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

@@ -373,7 +373,7 @@ describe('ReactComponentLifeCycle', () => {
     expect(instance.updater.isMounted(instance)).toBe(false);
   });
 
-  // @gate www && !disableLegacyMode
+  // @gate www && classic
   it('warns if legacy findDOMNode is used inside render', async () => {
     class Component extends React.Component {
       state = {isMounted: false};

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

@@ -14,12 +14,12 @@ const ReactDOM = require('react-dom');
 const StrictMode = React.StrictMode;
 
 describe('findDOMNode', () => {
-  // @gate www && !disableLegacyMode
+  // @gate www && classic
   it('findDOMNode should return null if passed null', () => {
     expect(ReactDOM.findDOMNode(null)).toBe(null);
   });
 
-  // @gate www && !disableLegacyMode
+  // @gate www && classic && !disableLegacyMode
   it('findDOMNode should find dom element', () => {
     class MyNode extends React.Component {
       render() {
@@ -39,7 +39,7 @@ describe('findDOMNode', () => {
     expect(mySameDiv).toBe(myDiv);
   });
 
-  // @gate www && !disableLegacyMode
+  // @gate www && classic && !disableLegacyMode
   it('findDOMNode should find dom element after an update from null', () => {
     function Bar({flag}) {
       if (flag) {
@@ -66,14 +66,14 @@ describe('findDOMNode', () => {
     expect(b.tagName).toBe('SPAN');
   });
 
-  // @gate www && !disableLegacyMode
+  // @gate www && classic
   it('findDOMNode should reject random objects', () => {
     expect(function () {
       ReactDOM.findDOMNode({foo: 'bar'});
     }).toThrowError('Argument appears to not be a ReactComponent. Keys: foo');
   });
 
-  // @gate www && !disableLegacyMode
+  // @gate www && classic && !disableLegacyMode
   it('findDOMNode should reject unmounted objects with render func', () => {
     class Foo extends React.Component {
       render() {
@@ -90,7 +90,7 @@ describe('findDOMNode', () => {
     );
   });
 
-  // @gate www && !disableLegacyMode
+  // @gate www && classic && !disableLegacyMode
   it('findDOMNode should not throw an error when called within a component that is not mounted', () => {
     class Bar extends React.Component {
       UNSAFE_componentWillMount() {
@@ -107,7 +107,7 @@ describe('findDOMNode', () => {
     }).not.toThrow();
   });
 
-  // @gate www && !disableLegacyMode
+  // @gate www && classic && !disableLegacyMode
   it('findDOMNode should warn if used to find a host component inside StrictMode', () => {
     let parent = undefined;
     let child = undefined;
@@ -141,7 +141,7 @@ describe('findDOMNode', () => {
     expect(match).toBe(child);
   });
 
-  // @gate www && !disableLegacyMode
+  // @gate www && classic && !disableLegacyMode
   it('findDOMNode should warn if passed a component that is inside StrictMode', () => {
     let parent = undefined;
     let child = undefined;

packages/shared/forks/ReactFeatureFlags.test-renderer.www.js

@@ -84,7 +84,7 @@ export const disableStringRefs = false;
 export const enableFastJSX = false;
 
 export const enableReactTestRendererWarning = false;
-export const disableLegacyMode = false;
+export const disableLegacyMode = true;
 
 export const disableDefaultPropsExceptForClasses = false;
 export const enableAddPropertiesFastPath = false;

packages/shared/forks/ReactFeatureFlags.www-dynamic.js

@@ -32,6 +32,7 @@ export const retryLaneExpirationMs = 5000;
 export const syncLaneExpirationMs = 250;
 export const transitionLaneExpirationMs = 5000;
 export const enableAddPropertiesFastPath = __VARIANT__;
+export const disableLegacyMode = __VARIANT__;
 
 // Enable this flag to help with concurrent mode debugging.
 // It logs information to the console about React scheduling, rendering, and commit phases.

packages/shared/forks/ReactFeatureFlags.www.js

@@ -119,7 +119,8 @@ export const useModernStrictMode = true;
 // because JSX is an extremely hot path.
 export const disableStringRefs = false;
 
-export const disableLegacyMode = __EXPERIMENTAL__;
+export const disableLegacyMode: boolean =
+  __EXPERIMENTAL__ || dynamicFeatureFlags.disableLegacyMode;
 
 export const enableOwnerStacks = false;
 export const enableShallowPropDiffing = false;