Only push newly created nodes on the parent stack

Previously I was pushing nodes on the parent stack regardless of whether they were already in current or not.
As a result, insertions during updates were duplicated, and nodes were added to existing parents before commit phase.
Luckily we have a test that caught that.

Author: gaearon

scripts/fiber/tests-failing.txt

@@ -48,7 +48,6 @@ src/renderers/dom/shared/wrappers/__tests__/ReactDOMInput-test.js
 src/renderers/dom/stack/client/__tests__/ReactDOM-test.js
 * throws in render() if the mount callback is not a function
 * throws in render() if the update callback is not a function
-* preserves focus
 
 src/renderers/dom/stack/client/__tests__/ReactMount-test.js
 * throws when given a non-node

scripts/fiber/tests-passing.txt

@@ -934,6 +934,7 @@ src/renderers/dom/stack/client/__tests__/ReactDOM-test.js
 * should overwrite props.children with children argument
 * should purge the DOM cache when removing nodes
 * allow React.DOM factories to be called without warnings
+* preserves focus
 
 src/renderers/dom/stack/client/__tests__/ReactMount-test.js
 * should render different components in same root

src/renderers/dom/stack/client/__tests__/ReactDOM-test.js

@@ -224,6 +224,7 @@ describe('ReactDOM', () => {
     });
 
     expect(document.activeElement.id).toBe('one');
+
     ReactDOM.render(<A showTwo={true} />, container);
     // input2 gets added, which causes input to get blurred. Then
     // componentDidUpdate focuses input2 and that should make it down to here,

src/renderers/shared/fiber/ReactFiberBeginWork.js

@@ -233,9 +233,9 @@ module.exports = function<T, P, I, TI, C>(
     }
     if (!current && workInProgress.stateNode == null) {
       const newProps = workInProgress.pendingProps;
-      const hostParent = getHostParentOnStack();
       const hostContainer = getHostContainerOnStack();
       const instance = createInstance(workInProgress.type, newProps, hostContainer, workInProgress);
+      const hostParent = getHostParentOnStack();
       if (hostParent) {
         // TODO: this breaks reuse?
         appendInitialChild(hostParent, instance);
@@ -278,7 +278,9 @@ module.exports = function<T, P, I, TI, C>(
       // Abort and don't process children yet.
       return null;
     } else {
-      pushHostParent(workInProgress.stateNode);
+      if (!current) {
+        pushHostParent(workInProgress.stateNode);
+      }
       if (isContainerType(workInProgress.type)) {
         pushHostContainer(workInProgress.stateNode);
       }
@@ -416,7 +418,9 @@ module.exports = function<T, P, I, TI, C>(
 
     // Put context on the stack because we will work on children
     if (isHostComponent) {
-      pushHostParent(workInProgress.stateNode);
+      if (!current) {
+        pushHostParent(workInProgress.stateNode);
+      }
       if (isContainerType(workInProgress.type)) {
         pushHostContainer(workInProgress.stateNode);
       }
@@ -503,9 +507,9 @@ module.exports = function<T, P, I, TI, C>(
           }
         }
         if (!current || workInProgress.stateNode == null) {
-          const hostParent = getHostParentOnStack();
           const textInstance = createTextInstance(newText, workInProgress);
           workInProgress.stateNode = textInstance;
+          const hostParent = getHostParentOnStack();
           if (hostParent) {
             // TODO: this breaks reuse?
             appendInitialChild(hostParent, textInstance);

src/renderers/shared/fiber/ReactFiberHostContext.js

@@ -25,6 +25,8 @@ let parentIndex = -1;
 const containerStack : Array = [];
 let containerIndex = -1;
 
+// TODO: this is all likely broken with portals.
+
 exports.getHostParentOnStack = function() : mixed | null {
   if (parentIndex === -1) {
     return null;