Implement findDOMNode for Fiber

This is the naive implementation that doesn't cover the case where there are
two diverging fibers, or if this tree is unmounted.

src/renderers/dom/fiber/ReactDOMFiber.js

@@ -146,6 +146,18 @@ var ReactDOM = {
     }
   },
 
+  findDOMNode(componentOrElement : Element | ?ReactComponent<any, any, any>) : null | Element | Text {
+    if (componentOrElement == null) {
+      return null;
+    }
+    // Unsound duck typing.
+    const component = (componentOrElement : any);
+    if (component.nodeType === 1) {
+      return component;
+    }
+    return DOMRenderer.findHostInstance(component);
+  },
+
 };
 
 module.exports = ReactDOM;

src/renderers/shared/fiber/ReactFiberReconciler.js

@@ -24,6 +24,8 @@ if (__DEV__) {
   var ReactFiberInstrumentation = require('ReactFiberInstrumentation');
 }
 
+var { findCurrentHostFiber } = require('ReactFiberTreeReflection');
+
 type Deadline = {
   timeRemaining : () => number
 };
@@ -58,17 +60,20 @@ export type HostConfig<T, P, I, TI, C> = {
 
 type OpaqueNode = Fiber;
 
-export type Reconciler<C, I> = {
+export type Reconciler<C, I, TI> = {
   mountContainer(element : ReactElement<any>, containerInfo : C) : OpaqueNode,
   updateContainer(element : ReactElement<any>, container : OpaqueNode) : void,
   unmountContainer(container : OpaqueNode) : void,
   performWithPriority(priorityLevel : PriorityLevel, fn : Function) : void,
 
   // Used to extract the return value from the initial render. Legacy API.
-  getPublicRootInstance(container : OpaqueNode) : (ReactComponent<any, any, any> | I | null),
+  getPublicRootInstance(container : OpaqueNode) : (ReactComponent<any, any, any> | TI | I | null),
+
+  // Use for findDOMNode/findHostNode. Legacy API.
+  findHostInstance(component : ReactComponent<any, any, any>) : I | TI | null,
 };
 
-module.exports = function<T, P, I, TI, C>(config : HostConfig<T, P, I, TI, C>) : Reconciler<C, I> {
+module.exports = function<T, P, I, TI, C>(config : HostConfig<T, P, I, TI, C>) : Reconciler<C, I, TI> {
 
   var { scheduleWork, performWithPriority } = ReactFiberScheduler(config);
 
@@ -122,7 +127,7 @@ module.exports = function<T, P, I, TI, C>(config : HostConfig<T, P, I, TI, C>) :
 
     performWithPriority,
 
-    getPublicRootInstance(container : OpaqueNode) : (ReactComponent<any, any, any> | I | null) {
+    getPublicRootInstance(container : OpaqueNode) : (ReactComponent<any, any, any> | I | TI | null) {
       const root : FiberRoot = (container.stateNode : any);
       const containerFiber = root.current;
       if (!containerFiber.child) {
@@ -131,6 +136,14 @@ module.exports = function<T, P, I, TI, C>(config : HostConfig<T, P, I, TI, C>) :
       return containerFiber.child.stateNode;
     },
 
+    findHostInstance(component : ReactComponent<any, any, any>) : I | TI | null {
+      const fiber = findCurrentHostFiber(component);
+      if (!fiber) {
+        return null;
+      }
+      return fiber.stateNode;
+    },
+
   };
 
 };

src/renderers/shared/fiber/ReactFiberTreeReflection.js

@@ -0,0 +1,54 @@
+/**
+ * Copyright 2013-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @providesModule ReactFiberTreeReflection
+ * @flow
+ */
+
+'use strict';
+
+import type { Fiber } from 'ReactFiber';
+
+var ReactInstanceMap = require('ReactInstanceMap');
+
+var {
+  ClassComponent,
+  HostContainer,
+  HostComponent,
+  HostText,
+} = require('ReactTypeOfWork');
+
+exports.findCurrentHostFiber = function(component : ReactComponent<any, any, any>) : Fiber | null {
+  var parent : ?Fiber = ReactInstanceMap.get(component);
+  if (!parent) {
+    return null;
+  }
+
+  // TODO: This search is incomplete because this could be one of two possible fibers.
+  let node : Fiber = parent;
+  while (true) {
+    if (node.tag === HostComponent || node.tag === HostText) {
+      return node;
+    } else if (node.child) {
+      // TODO: Coroutines need to visit the stateNode.
+      node = node.child;
+      continue;
+    }
+    if (node === parent) {
+      return null;
+    }
+    while (!node.sibling) {
+      if (!node.return || node.return === parent) {
+        return null;
+      }
+      node = node.return;
+    }
+    node = node.sibling;
+  }
+  return null;
+};