Warn if accessing .type on a factory

This was an important convenience as an upgrade path but shouldn't be
necessary if you're using best-practice of calling createFactory in the
consuming component.

src/classic/element/ReactElementValidator.js

@@ -387,6 +387,33 @@ var ReactElementValidator = {
     );
     // Legacy hook TODO: Warn if this is accessed
     validatedFactory.type = type;
+
+    if (__DEV__) {
+      try {
+        Object.defineProperty(
+          validatedFactory,
+          'type',
+          {
+            enumerable: false,
+            get: function() {
+              warning(
+                false,
+                'Factory.type is deprecated. Access the class directly ' +
+                'before passing it to createFactory.'
+              );
+              Object.defineProperty(this, 'type', {
+                value: type
+              });
+              return type;
+            }
+          }
+        );
+      } catch (x) {
+        // IE will fail on defineProperty (es5-shim/sham too)
+      }
+    }
+
+
     return validatedFactory;
   }
 

src/classic/element/__tests__/ReactElementValidator-test.js

@@ -330,4 +330,23 @@ describe('ReactElementValidator', function() {
     expect(console.warn.calls[0].args[0]).toContain('use of a keyed object');
   });
 
+  it('should warn when accessing .type on an element factory', function() {
+    spyOn(console, 'warn');
+    var TestComponent = React.createClass({
+      render: function() {
+        return <div />;
+      }
+    });
+    var TestFactory = React.createFactory(TestComponent);
+    expect(TestFactory.type).toBe(TestComponent);
+    expect(console.warn.argsForCall.length).toBe(1);
+    expect(console.warn.argsForCall[0][0]).toBe(
+      'Warning: Factory.type is deprecated. Access the class directly before ' +
+      'passing it to createFactory.'
+    );
+    // Warn once, not again
+    expect(TestFactory.type).toBe(TestComponent);
+    expect(console.warn.argsForCall.length).toBe(1);
+  });
+
 });