Turn on string ref deprecation warning for everybody (not codemoddabl…

…e) (#25383)

## Summary
 
Alternate to #25334 without any
prod runtime changes i.e. the proposed codemod in
https://github.com/reactjs/rfcs/blob/createlement-rfc/text/0000-create-element-changes.md#deprecate-string-refs-and-remove-production-mode-_owner-field
would not work.

## How did you test this change?

- [x] CI
- [x] `yarn test` with and without `warnAboutStringRefs`

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

@@ -12,6 +12,7 @@
 let React;
 let ReactDOM;
 let ReactDOMServer;
+let ReactFeatureFlags;
 let ReactTestUtils;
 
 describe('ReactComponent', () => {
@@ -21,6 +22,7 @@ describe('ReactComponent', () => {
     React = require('react');
     ReactDOM = require('react-dom');
     ReactDOMServer = require('react-dom/server');
+    ReactFeatureFlags = require('shared/ReactFeatureFlags');
     ReactTestUtils = require('react-dom/test-utils');
   });
 
@@ -36,7 +38,7 @@ describe('ReactComponent', () => {
     }).toThrowError(/Target container is not a DOM element./);
   });
 
-  it('should throw when supplying a ref outside of render method', () => {
+  it('should throw when supplying a string ref outside of render method', () => {
     let instance = <div ref="badDiv" />;
     expect(function() {
       instance = ReactTestUtils.renderIntoDocument(instance);
@@ -102,7 +104,7 @@ describe('ReactComponent', () => {
     }
   });
 
-  it('should support refs on owned components', () => {
+  it('should support string refs on owned components', () => {
     const innerObj = {};
     const outerObj = {};
 
@@ -133,10 +135,29 @@ describe('ReactComponent', () => {
       }
     }
 
-    ReactTestUtils.renderIntoDocument(<Component />);
+    expect(() => {
+      ReactTestUtils.renderIntoDocument(<Component />);
+    }).toErrorDev(
+      ReactFeatureFlags.warnAboutStringRefs
+        ? [
+            'Warning: Component "div" contains the string ref "inner". ' +
+              'Support for string refs will be removed in a future major release. ' +
+              'We recommend using useRef() or createRef() instead. ' +
+              'Learn more about using refs safely here: https://reactjs.org/link/strict-mode-string-ref\n' +
+              '    in div (at **)\n' +
+              '    in Wrapper (at **)\n' +
+              '    in Component (at **)',
+            'Warning: Component "Component" contains the string ref "outer". ' +
+              'Support for string refs will be removed in a future major release. ' +
+              'We recommend using useRef() or createRef() instead. ' +
+              'Learn more about using refs safely here: https://reactjs.org/link/strict-mode-string-ref\n' +
+              '    in Component (at **)',
+          ]
+        : [],
+    );
   });
 
-  it('should not have refs on unmounted components', () => {
+  it('should not have string refs on unmounted components', () => {
     class Parent extends React.Component {
       render() {
         return (

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

@@ -378,7 +378,7 @@ describe('ReactComponentLifeCycle', () => {
         }
         // you would *NEVER* do anything like this in real code!
         this.state.hasRenderCompleted = true;
-        return <div ref="theDiv">I am the inner DIV</div>;
+        return <div ref={React.createRef()}>I am the inner DIV</div>;
       }
 
       componentWillUnmount() {
@@ -477,7 +477,9 @@ describe('ReactComponentLifeCycle', () => {
     class Component extends React.Component {
       render() {
         return (
-          <Tooltip ref="tooltip" tooltip={<div>{this.props.tooltipText}</div>}>
+          <Tooltip
+            ref={React.createRef()}
+            tooltip={<div>{this.props.tooltipText}</div>}>
             {this.props.text}
           </Tooltip>
         );

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

@@ -72,16 +72,18 @@ describe('ReactCompositeComponent', () => {
     MorphingComponent = class extends React.Component {
       state = {activated: false};
 
+      xRef = React.createRef();
+
       _toggleActivatedState = () => {
         this.setState({activated: !this.state.activated});
       };
 
       render() {
         const toggleActivatedState = this._toggleActivatedState;
         return !this.state.activated ? (
-          <a ref="x" onClick={toggleActivatedState} />
+          <a ref={this.xRef} onClick={toggleActivatedState} />
         ) : (
-          <b ref="x" onClick={toggleActivatedState} />
+          <b ref={this.xRef} onClick={toggleActivatedState} />
         );
       }
     };
@@ -91,14 +93,16 @@ describe('ReactCompositeComponent', () => {
      * reallocated again.
      */
     ChildUpdates = class extends React.Component {
+      anchorRef = React.createRef();
+
       getAnchor = () => {
-        return this.refs.anch;
+        return this.anchorRef.current;
       };
 
       render() {
         const className = this.props.anchorClassOn ? 'anchorClass' : '';
         return this.props.renderAnchor ? (
-          <a ref="anch" className={className} />
+          <a ref={this.anchorRef} className={className} />
         ) : (
           <b />
         );
@@ -186,11 +190,11 @@ describe('ReactCompositeComponent', () => {
   it('should rewire refs when rendering to different child types', () => {
     const instance = ReactTestUtils.renderIntoDocument(<MorphingComponent />);
 
-    expect(instance.refs.x.tagName).toBe('A');
+    expect(instance.xRef.current.tagName).toBe('A');
     instance._toggleActivatedState();
-    expect(instance.refs.x.tagName).toBe('B');
+    expect(instance.xRef.current.tagName).toBe('B');
     instance._toggleActivatedState();
-    expect(instance.refs.x.tagName).toBe('A');
+    expect(instance.xRef.current.tagName).toBe('A');
   });
 
   it('should not cache old DOM nodes when switching constructors', () => {
@@ -739,25 +743,28 @@ describe('ReactCompositeComponent', () => {
     }
 
     class Wrapper extends React.Component {
+      parentRef = React.createRef();
+      childRef = React.createRef();
+
       render() {
         return (
-          <Parent ref="parent">
-            <Child ref="child" />
+          <Parent ref={this.parentRef}>
+            <Child ref={this.childRef} />
           </Parent>
         );
       }
     }
 
     const wrapper = ReactTestUtils.renderIntoDocument(<Wrapper />);
 
-    expect(wrapper.refs.parent.state.flag).toEqual(true);
-    expect(wrapper.refs.child.context).toEqual({flag: true});
+    expect(wrapper.parentRef.current.state.flag).toEqual(true);
+    expect(wrapper.childRef.current.context).toEqual({flag: true});
 
     // We update <Parent /> while <Child /> is still a static prop relative to this update
-    wrapper.refs.parent.setState({flag: false});
+    wrapper.parentRef.current.setState({flag: false});
 
-    expect(wrapper.refs.parent.state.flag).toEqual(false);
-    expect(wrapper.refs.child.context).toEqual({flag: false});
+    expect(wrapper.parentRef.current.state.flag).toEqual(false);
+    expect(wrapper.childRef.current.context).toEqual({flag: false});
   });
 
   it('should pass context transitively', () => {
@@ -1142,25 +1149,28 @@ describe('ReactCompositeComponent', () => {
     }
 
     class Component extends React.Component {
+      static0Ref = React.createRef();
+      static1Ref = React.createRef();
+
       render() {
         if (this.props.flipped) {
           return (
             <div>
-              <Static ref="static0" key="B">
+              <Static ref={this.static0Ref} key="B">
                 B (ignored)
               </Static>
-              <Static ref="static1" key="A">
+              <Static ref={this.static1Ref} key="A">
                 A (ignored)
               </Static>
             </div>
           );
         } else {
           return (
             <div>
-              <Static ref="static0" key="A">
+              <Static ref={this.static0Ref} key="A">
                 A
               </Static>
-              <Static ref="static1" key="B">
+              <Static ref={this.static1Ref} key="B">
                 B
               </Static>
             </div>
@@ -1171,14 +1181,14 @@ describe('ReactCompositeComponent', () => {
 
     const container = document.createElement('div');
     const comp = ReactDOM.render(<Component flipped={false} />, container);
-    expect(ReactDOM.findDOMNode(comp.refs.static0).textContent).toBe('A');
-    expect(ReactDOM.findDOMNode(comp.refs.static1).textContent).toBe('B');
+    expect(ReactDOM.findDOMNode(comp.static0Ref.current).textContent).toBe('A');
+    expect(ReactDOM.findDOMNode(comp.static1Ref.current).textContent).toBe('B');
 
     // When flipping the order, the refs should update even though the actual
     // contents do not
     ReactDOM.render(<Component flipped={true} />, container);
-    expect(ReactDOM.findDOMNode(comp.refs.static0).textContent).toBe('B');
-    expect(ReactDOM.findDOMNode(comp.refs.static1).textContent).toBe('A');
+    expect(ReactDOM.findDOMNode(comp.static0Ref.current).textContent).toBe('B');
+    expect(ReactDOM.findDOMNode(comp.static1Ref.current).textContent).toBe('A');
   });
 
   it('should allow access to findDOMNode in componentWillUnmount', () => {
@@ -1453,10 +1463,11 @@ describe('ReactCompositeComponent', () => {
         this.state = {
           color: 'green',
         };
+        this.appleRef = React.createRef();
       }
 
       render() {
-        return <Apple color={this.state.color} ref="apple" />;
+        return <Apple color={this.state.color} ref={this.appleRef} />;
       }
     }
 
@@ -1502,15 +1513,15 @@ describe('ReactCompositeComponent', () => {
     expect(renderCalls).toBe(2);
 
     // Re-render base on state
-    instance.refs.apple.cut();
+    instance.appleRef.current.cut();
     expect(renderCalls).toBe(3);
 
     // No re-render based on state
-    instance.refs.apple.cut();
+    instance.appleRef.current.cut();
     expect(renderCalls).toBe(3);
 
     // Re-render based on state again
-    instance.refs.apple.eatSlice();
+    instance.appleRef.current.eatSlice();
     expect(renderCalls).toBe(4);
   });
 

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

@@ -193,12 +193,13 @@ describe('ReactDOMEventListener', () => {
     const onMouseOut = event => mouseOut(event.target);
 
     class Wrapper extends React.Component {
+      innerRef = React.createRef();
       getInner = () => {
-        return this.refs.inner;
+        return this.innerRef.current;
       };
 
       render() {
-        const inner = <div ref="inner">Inner</div>;
+        const inner = <div ref={this.innerRef}>Inner</div>;
         return (
           <div>
             <div onMouseOut={onMouseOut} id="outer">

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

@@ -1071,22 +1071,31 @@ describe('ReactDOMInput', () => {
 
   it('should control radio buttons', () => {
     class RadioGroup extends React.Component {
+      aRef = React.createRef();
+      bRef = React.createRef();
+      cRef = React.createRef();
+
       render() {
         return (
           <div>
             <input
-              ref="a"
+              ref={this.aRef}
               type="radio"
               name="fruit"
               checked={true}
               onChange={emptyFunction}
             />
             A
-            <input ref="b" type="radio" name="fruit" onChange={emptyFunction} />
+            <input
+              ref={this.bRef}
+              type="radio"
+              name="fruit"
+              onChange={emptyFunction}
+            />
             B
             <form>
               <input
-                ref="c"
+                ref={this.cRef}
                 type="radio"
                 name="fruit"
                 defaultChecked={true}
@@ -1099,9 +1108,9 @@ describe('ReactDOMInput', () => {
     }
 
     const stub = ReactDOM.render(<RadioGroup />, container);
-    const aNode = stub.refs.a;
-    const bNode = stub.refs.b;
-    const cNode = stub.refs.c;
+    const aNode = stub.aRef.current;
+    const bNode = stub.bRef.current;
+    const cNode = stub.cRef.current;
 
     expect(aNode.checked).toBe(true);
     expect(bNode.checked).toBe(false);

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

@@ -337,7 +337,7 @@ describe('ReactDOMServerIntegration', () => {
       itRenders('no ref attribute', async render => {
         class RefComponent extends React.Component {
           render() {
-            return <div ref="foo" />;
+            return <div ref={React.createRef()} />;
           }
         }
         const e = await render(<RefComponent />);

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

@@ -14,6 +14,7 @@ const ReactDOMServerIntegrationUtils = require('./utils/ReactDOMServerIntegratio
 let React;
 let ReactDOM;
 let ReactDOMServer;
+let ReactFeatureFlags;
 let ReactTestUtils;
 
 function initModules() {
@@ -22,6 +23,7 @@ function initModules() {
   React = require('react');
   ReactDOM = require('react-dom');
   ReactDOMServer = require('react-dom/server');
+  ReactFeatureFlags = require('shared/ReactFeatureFlags');
   ReactTestUtils = require('react-dom/test-utils');
 
   // Make them available to the helpers.
@@ -91,10 +93,22 @@ describe('ReactDOMServerIntegration', () => {
       root.innerHTML = markup;
       let component = null;
       resetModules();
-      await asyncReactDOMRender(
-        <RefsComponent ref={e => (component = e)} />,
-        root,
-        true,
+      await expect(async () => {
+        await asyncReactDOMRender(
+          <RefsComponent ref={e => (component = e)} />,
+          root,
+          true,
+        );
+      }).toErrorDev(
+        ReactFeatureFlags.warnAboutStringRefs
+          ? [
+              'Warning: Component "RefsComponent" contains the string ref "myDiv". ' +
+                'Support for string refs will be removed in a future major release. ' +
+                'We recommend using useRef() or createRef() instead. ' +
+                'Learn more about using refs safely here: https://reactjs.org/link/strict-mode-string-ref\n' +
+                '    in RefsComponent (at **)',
+            ]
+          : [],
       );
       expect(component.refs.myDiv).toBe(root.firstChild);
     });

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

@@ -67,17 +67,18 @@ describe('ReactIdentity', () => {
 
   function renderAComponentWithKeyIntoContainer(key, container) {
     class Wrapper extends React.Component {
+      spanRef = React.createRef();
       render() {
         return (
           <div>
-            <span ref="span" key={key} />
+            <span ref={this.spanRef} key={key} />
           </div>
         );
       }
     }
 
     const instance = ReactDOM.render(<Wrapper />, container);
-    const span = instance.refs.span;
+    const span = instance.spanRef.current;
     expect(span).not.toBe(null);
   }