[Portal] Global option to disable the portal

docs/src/pages/guides/composition/composition.md

@@ -89,6 +89,6 @@ class ListItemLink extends React.Component {
 }
 ```
 
-`renderLink` will now always reference the same component. Here is a demo:
+`renderLink` will now always reference the same component. Here is a demo with react-router:
 
 {{"demo": "pages/guides/composition/ComponentProperty.js"}}

packages/material-ui/src/Portal/Portal.js

@@ -1,3 +1,5 @@
+/* eslint-disable no-underscore-dangle */
+
 import React from 'react';
 import ReactDOM from 'react-dom';
 import PropTypes from 'prop-types';
@@ -44,13 +46,30 @@ class Portal extends React.Component {
    * @public
    */
   getMountNode = () => {
+    if (this.disable) {
+      return ReactDOM.findDOMNode(this);
+    }
+
     return this.mountNode;
   };
 
+  // Hack waiting for https://github.com/airbnb/enzyme/issues/252 to be solved.
+  // When `__MUI_PORTAL_DISABLE__` is set to `true`,
+  // the portal will behave as a pass-through component.
+  disable = typeof global !== 'undefined' && global.__MUI_PORTAL_DISABLE__;
+
   render() {
     const { children } = this.props;
 
-    return this.mountNode ? ReactDOM.createPortal(children, this.mountNode) : null;
+    if (this.mountNode) {
+      if (this.disable) {
+        return children;
+      }
+
+      return ReactDOM.createPortal(children, this.mountNode);
+    }
+
+    return null;
   }
 }
 

packages/material-ui/src/Portal/Portal.test.js

@@ -1,3 +1,4 @@
+/* eslint-disable no-underscore-dangle */
 /* eslint-disable react/no-multi-comp */
 
 import React from 'react';
@@ -24,6 +25,29 @@ describe('<Portal />', () => {
     mount.cleanUp();
   });
 
+  describe('disable portal for tests', () => {
+    const Portal = NewPortal;
+
+    before(() => {
+      global.__MUI_PORTAL_DISABLE__ = true;
+    });
+
+    after(() => {
+      global.__MUI_PORTAL_DISABLE__ = false;
+    });
+
+    it('should disable the portal feature', () => {
+      const wrapper = mount(
+        <Portal>
+          <h1 className="woofPortal">Foo</h1>
+        </Portal>,
+      );
+      assert.strictEqual(wrapper.children().length, 1, 'should have one children');
+      const instance = wrapper.instance();
+      assert.strictEqual(instance.getMountNode().nodeName.toLowerCase(), 'h1');
+    });
+  });
+
   versions.map(verion => {
     describe(verion, () => {
       let Portal;