Constructor error message

packages/react-reconciler/src/ReactFiberClassComponent.js

@@ -201,12 +201,22 @@ module.exports = function(
     if (__DEV__) {
       const name = getComponentName(workInProgress);
       const renderPresent = instance.render;
-      warning(
-        renderPresent,
-        '%s(...): No `render` method found on the returned component ' +
-          'instance: you may have forgotten to define `render`.',
-        name,
-      );
+
+      if (type.prototype && type.prototype.render !== undefined) {
+        warning(
+          renderPresent,
+          '%s(...): No `render` method found on the returned component ' +
+            'instance: is the `constructor` defined well?',
+          name,
+        );
+      } else {
+        warning(
+          renderPresent,
+          '%s(...): No `render` method found on the returned component ' +
+            'instance: you may have forgotten to define `render`.',
+          name,
+        );
+      }
       const noGetInitialStateOnES6 =
         !instance.getInitialState ||
         instance.getInitialState.isReactClassApproved ||

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

@@ -0,0 +1,60 @@
+describe('ReactFiberClassComponent', () => {
+  let React;
+  let ReactNoop;
+
+  beforeEach(() => {
+    jest.resetModules();
+    React = require('react');
+    ReactNoop = require('react-noop-renderer');
+  });
+
+  it('should render a class if nominal', () => {
+    class NominalComponent extends React.Component {
+      render() {
+        return <div />;
+      }
+    }
+
+    ReactNoop.render(<NominalComponent />);
+    ReactNoop.flush();
+  });
+
+  it('should return a meaningful warning when constructor is returned', () => {
+    spyOn(console, 'error');
+    class RenderTextInvalidConstructor extends React.Component {
+      constructor(props) {
+        super(props);
+        return {something: false};
+      }
+
+      render() {
+        return <div />;
+      }
+    }
+
+    ReactNoop.render(<RenderTextInvalidConstructor />);
+    ReactNoop.flushUnitsOfWork(2);
+
+    const error = console.error.calls.mostRecent().args[0];
+
+    expectDev(error).toBe(
+      'Warning: RenderTextInvalidConstructor(...): No `render` method found on the returned ' +
+        'component instance: is the `constructor` defined well?',
+    );
+  });
+
+  it('should return error if render is not defined', () => {
+    spyOn(console, 'error');
+    class RenderTestUndefinedRender extends React.Component {}
+
+    ReactNoop.render(<RenderTestUndefinedRender />);
+    ReactNoop.flushUnitsOfWork(2);
+
+    const error = console.error.calls.mostRecent().args[0];
+
+    expectDev(error).toBe(
+      'Warning: RenderTestUndefinedRender(...): No `render` method found on the returned ' +
+        'component instance: you may have forgotten to define `render`.',
+    );
+  });
+});