Add warning in server renderer if class doesn't extend React.Component (

facebook#11993)

* Add warning in server renderer if class doesn't extend React.Component

In dev mode, while server rendering, a warning will be thrown if there is a class that doesn't extend React.Component.

* Use `.toWarnDev` matcher and deduplicate warnings

* Deduplicate client-side warning if class doesn't extend React.Component

* Default componentName to Unknown if null

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

@@ -338,6 +338,11 @@ describe('ReactCompositeComponent', () => {
           'Change ClassWithRenderNotExtended to extend React.Component instead.',
       );
     }).toThrow(TypeError);
+
+    // Test deduplication
+    expect(() => {
+      ReactDOM.render(<ClassWithRenderNotExtended />, container);
+    }).toThrow(TypeError);
   });
 
   it('should warn about `setState` in render', () => {

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

@@ -554,4 +554,27 @@ describe('ReactDOMServer', () => {
       'The experimental Call and Return types are not currently supported by the server renderer.',
     );
   });
+
+  it('should warn when server rendering a class with a render method that does not extend React.Component', () => {
+    class ClassWithRenderNotExtended {
+      render() {
+        return <div />;
+      }
+    }
+
+    expect(() => {
+      expect(() =>
+        ReactDOMServer.renderToString(<ClassWithRenderNotExtended />),
+      ).toWarnDev(
+        'Warning: The <ClassWithRenderNotExtended /> component appears to have a render method, ' +
+          "but doesn't extend React.Component. This is likely to cause errors. " +
+          'Change ClassWithRenderNotExtended to extend React.Component instead.',
+      );
+    }).toThrow(TypeError);
+
+    // Test deduplication
+    expect(() => {
+      ReactDOMServer.renderToString(<ClassWithRenderNotExtended />);
+    }).toThrow(TypeError);
+  });
 });

packages/react-dom/src/server/ReactPartialRenderer.js

@@ -122,6 +122,7 @@ let didWarnDefaultSelectValue = false;
 let didWarnDefaultTextareaValue = false;
 let didWarnInvalidOptionChildren = false;
 const didWarnAboutNoopUpdateForComponent = {};
+const didWarnAboutBadClass = {};
 const valuePropNames = ['value', 'defaultValue'];
 const newlineEatingTags = {
   listing: true,
@@ -421,6 +422,25 @@ function resolve(
     if (shouldConstruct(Component)) {
       inst = new Component(element.props, publicContext, updater);
     } else {
+      if (__DEV__) {
+        if (
+          Component.prototype &&
+          typeof Component.prototype.render === 'function'
+        ) {
+          const componentName = getComponentName(Component) || 'Unknown';
+
+          if (!didWarnAboutBadClass[componentName]) {
+            warning(
+              false,
+              "The <%s /> component appears to have a render method, but doesn't extend React.Component. " +
+                'This is likely to cause errors. Change %s to extend React.Component instead.',
+              componentName,
+              componentName,
+            );
+            didWarnAboutBadClass[componentName] = true;
+          }
+        }
+      }
       inst = Component(element.props, publicContext, updater);
       if (inst == null || inst.render == null) {
         child = inst;

packages/react-reconciler/src/ReactFiberBeginWork.js

@@ -61,9 +61,11 @@ import {NoWork, Never} from './ReactFiberExpirationTime';
 import {AsyncUpdates} from './ReactTypeOfInternalContext';
 
 let warnedAboutStatelessRefs;
+let didWarnAboutBadClass;
 
 if (__DEV__) {
   warnedAboutStatelessRefs = {};
+  didWarnAboutBadClass = {};
 }
 
 export default function<T, P, I, TI, HI, PI, C, CC, CX, PL>(
@@ -455,14 +457,18 @@ export default function<T, P, I, TI, HI, PI, C, CC, CX, PL>(
 
     if (__DEV__) {
       if (fn.prototype && typeof fn.prototype.render === 'function') {
-        const componentName = getComponentName(workInProgress);
-        warning(
-          false,
-          "The <%s /> component appears to have a render method, but doesn't extend React.Component. " +
-            'This is likely to cause errors. Change %s to extend React.Component instead.',
-          componentName,
-          componentName,
-        );
+        const componentName = getComponentName(workInProgress) || 'Unknown';
+
+        if (!didWarnAboutBadClass[componentName]) {
+          warning(
+            false,
+            "The <%s /> component appears to have a render method, but doesn't extend React.Component. " +
+              'This is likely to cause errors. Change %s to extend React.Component instead.',
+            componentName,
+            componentName,
+          );
+          didWarnAboutBadClass[componentName] = true;
+        }
       }
       ReactCurrentOwner.current = workInProgress;
       value = fn(props, context);