Revert "Support writing to this.refs from userspace" (facebook#28877)

Reverts facebook#28867 It broke some tests, reverting until we figure out why to avoid having too much delay in the sync.

Author: kassens

packages/react-reconciler/src/ReactFiberClassComponent.js

@@ -819,6 +819,7 @@ function mountClassInstance(
  const instance = workInProgress.stateNode;
  instance.props = newProps;
  instance.state = workInProgress.memoizedState;
+ instance.refs = {};
 
  initializeUpdateQueue(workInProgress);
 

packages/react-reconciler/src/__tests__/ReactFiberRefs-test.js

@@ -138,28 +138,4 @@ describe('ReactFiberRefs', () => {
  );
  expect(refProp).toBe('child');
  });
-
- test('strings refs can be codemodded to callback refs', async () => {
- let app;
- class App extends React.Component {
- render() {
- app = this;
- return (
- <div
- prop="Hello!"
- ref={el => {
- // `refs` used to be a shared frozen object unless/until a string
- // ref attached by the reconciler, but it's not anymore so that we
- // can codemod string refs to userspace callback refs.
- this.refs.div = el;
- }}
- />
- );
- }
- }
-
- const root = ReactNoop.createRoot();
- await act(() => root.render(<App />));
- expect(app.refs.div.prop).toBe('Hello!');
- });
 });

packages/react/src/ReactBaseClasses.js

@@ -8,13 +8,19 @@
 import ReactNoopUpdateQueue from './ReactNoopUpdateQueue';
 import assign from 'shared/assign';
 
+const emptyObject = {};
+if (__DEV__) {
+ Object.freeze(emptyObject);
+}
+
 /**
  * Base class helpers for the updating state of a component.
  */
 function Component(props, context, updater) {
  this.props = props;
  this.context = context;
- this.refs = {};
+ // If a component has string refs, we will assign a different object later.
+ this.refs = emptyObject;
  // We initialize the default updater but the real one gets injected by the
  // renderer.
  this.updater = updater || ReactNoopUpdateQueue;
@@ -127,7 +133,7 @@ function PureComponent(props, context, updater) {
  this.props = props;
  this.context = context;
  // If a component has string refs, we will assign a different object later.
- this.refs = {};
+ this.refs = emptyObject;
  this.updater = updater || ReactNoopUpdateQueue;
 }