Warn for functional refs on stateless functional components

src/renderers/shared/stack/reconciler/ReactRef.js

@@ -13,6 +13,7 @@
 'use strict';
 
 var ReactOwner = require('ReactOwner');
+var warning = require('warning');
 
 import type { ReactInstance } from 'ReactInstanceType';
 import type { ReactElement } from 'ReactElementType';
@@ -21,7 +22,18 @@ var ReactRef = {};
 
 function attachRef(ref, component, owner) {
   if (typeof ref === 'function') {
-    ref(component.getPublicInstance());
+    var instance = component.getPublicInstance();
+    if (__DEV__) {
+      var componentName = component && component.getName ?
+        component.getName() : 'a component';
+      warning(instance != null,
+        'Stateless function components cannot be given refs ' +
+        '(See %s%s).',
+        componentName,
+        owner ? ' created by ' + owner.getName() : ''
+      );
+    }
+    ref(instance);
   } else {
     // Legacy ref
     ReactOwner.addComponentAsRefTo(

src/renderers/shared/stack/reconciler/__tests__/ReactStatelessComponent-test.js

@@ -146,7 +146,25 @@ describe('ReactStatelessComponent', () => {
     );
   });
 
-  it('should warn when given a ref', () => {
+  it('should warn for functional refs in pure functions', function() {
+    spyOn(console, 'error');
+
+    var Parent = React.createClass({
+      displayName: 'Parent',
+      render: function() {
+        return <StatelessComponent name="A" ref={() => {}}/>;
+      },
+    });
+
+    ReactTestUtils.renderIntoDocument(<Parent />);
+    expect(console.error.calls.count()).toBe(1);
+    expect(console.error.calls.argsFor(0)[0]).toContain(
+      'Stateless function components cannot be given refs ' +
+      '(See StatelessComponent created by Parent).',
+    );
+  });
+
+  it('should warn when given a ref', function() {
     spyOn(console, 'error');
 
     class Parent extends React.Component {