Added unit tests for creating an element with a ref in a constructor. Only set ReactCurrentOwner.current in dev mode when the component has no constructor. (#10025)

nhunzaker: I've added an additional line to the ref test that sets the
NODE_ENV invironment variable. This allows the test to pass.

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

@@ -372,7 +372,7 @@ var ReactCompositeComponent = {
     publicContext,
     updateQueue,
   ) {
-    if (__DEV__) {
+    if (__DEV__ && !doConstruct) {
       ReactCurrentOwner.current = this;
       try {
         return this._constructComponentWithoutOwner(

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

@@ -13,6 +13,7 @@
 
 var React = require('React');
 var ReactTestUtils = require('ReactTestUtils');
+var ReactDOMFeatureFlags = require('ReactDOMFeatureFlags');
 
 var reactComponentExpect = require('reactComponentExpect');
 
@@ -283,3 +284,78 @@ describe('ref swapping', () => {
     __DEV__ = originalDev;
   });
 });
+
+describe('creating element with ref in constructor', () => {
+  class RefTest extends React.Component {
+    constructor(props) {
+      super(props);
+      this.p = <p ref="p">Hello!</p>;
+    }
+
+    render() {
+      return <div>{this.p}</div>;
+    }
+  }
+
+  var devErrorMessage =
+    'addComponentAsRefTo(...): Only a ReactOwner can have refs. You might ' +
+    "be adding a ref to a component that was not created inside a component's " +
+    '`render` method, or you have multiple copies of React loaded ' +
+    '(details: https://fb.me/react-refs-must-have-owner).';
+
+  var prodErrorMessage =
+    'Minified React error #119; visit ' +
+    'http://facebook.github.io/react/docs/error-decoder.html?invariant=119 for the full message ' +
+    'or use the non-minified dev environment for full errors and additional helpful warnings.';
+
+  var fiberDevErrorMessage =
+    'Element ref was specified as a string (p) but no owner was ' +
+    'set. You may have multiple copies of React loaded. ' +
+    '(details: https://fb.me/react-refs-must-have-owner).';
+
+  var fiberProdErrorMessage =
+    'Minified React error #149; visit ' +
+    'http://facebook.github.io/react/docs/error-decoder.html?invariant=149&args[]=p ' +
+    'for the full message or use the non-minified dev environment for full errors and additional ' +
+    'helpful warnings.';
+
+  it('throws an error when __DEV__ = true', () => {
+    ReactTestUtils = require('ReactTestUtils');
+
+    var originalDev = __DEV__;
+    __DEV__ = true;
+
+    try {
+      expect(function() {
+        ReactTestUtils.renderIntoDocument(<RefTest />);
+      }).toThrowError(
+        ReactDOMFeatureFlags.useFiber ? fiberDevErrorMessage : devErrorMessage,
+      );
+    } finally {
+      __DEV__ = originalDev;
+    }
+  });
+
+  it('throws an error when __DEV__ = false', () => {
+    ReactTestUtils = require('ReactTestUtils');
+
+    var originalDev = __DEV__;
+    var originalEnv = process.env.NODE_ENV;
+
+    __DEV__ = false;
+    process.env.NODE_ENV = 'production';
+
+    try {
+      expect(function() {
+        ReactTestUtils.renderIntoDocument(<RefTest />);
+      }).toThrowError(
+        ReactDOMFeatureFlags.useFiber
+          ? fiberProdErrorMessage
+          : prodErrorMessage,
+      );
+    } finally {
+      __DEV__ = originalDev;
+      process.env.NODE_ENV = originalEnv;
+    }
+  });
+});