[WIP][Fiber] Make Fiber a disjoint union based on the tag

src/isomorphic/hooks/ReactComponentTreeHook.js

@@ -325,7 +325,7 @@ var ReactComponentTreeHook = {
 
     var currentOwner = ReactCurrentOwner.current;
     if (currentOwner && typeof currentOwner._debugID === 'number') {
-      var id = currentOwner && currentOwner._debugID;
+      var id = currentOwner ? currentOwner._debugID : null;
       info += ReactComponentTreeHook.getStackAddendumByID(id);
     }
     return info;

src/renderers/noop/ReactNoop.js

@@ -305,11 +305,11 @@ var ReactNoop = {
 
     function logFiber(fiber : Fiber, depth) {
       log(
-        '  '.repeat(depth) + '- ' + (fiber.type ? fiber.type.name || fiber.type : '[root]'),
+        '  '.repeat(depth) + '- ' + (fiber.type ? (fiber.type : any).name || fiber.type : '[root]'),
         '[' + fiber.pendingWorkPriority + (fiber.pendingProps ? '*' : '') + ']'
       );
-      if (fiber.updateQueue) {
-        logUpdateQueue(fiber.updateQueue, depth);
+      if ((fiber : any).updateQueue) {
+        logUpdateQueue((fiber : any).updateQueue, depth);
       }
       const childInProgress = fiber.progressedChild;
       if (childInProgress && childInProgress !== fiber.child) {
@@ -332,7 +332,7 @@ var ReactNoop = {
     log('HOST INSTANCES:');
     logContainer(rootContainer, 0);
     log('FIBERS:');
-    logFiber((root.stateNode : any).current, 0);
+    logFiber((root : any).stateNode.current, 0);
 
     console.log(...bufferedLog);
   },

src/renderers/shared/fiber/ReactChildFiber.js

@@ -14,7 +14,11 @@
 
 import type { ReactCoroutine, ReactYield } from 'ReactCoroutine';
 import type { ReactPortal } from 'ReactPortal';
-import type { Fiber } from 'ReactFiber';
+import type {
+  Fiber,
+  ElementFiber,
+  ParentFiber,
+} from 'ReactFiber';
 import type { ReactInstance } from 'ReactInstanceType';
 import type { PriorityLevel } from 'ReactPriorityLevel';
 
@@ -55,6 +59,8 @@ const isArray = Array.isArray;
 
 const {
   ClassComponent,
+  FunctionalComponent,
+  HostComponent,
   HostText,
   HostPortal,
   CoroutineComponent,
@@ -68,7 +74,11 @@ const {
   Deletion,
 } = ReactTypeOfSideEffect;
 
-function coerceRef(current: ?Fiber, element: ReactElement<any>) {
+function coerceRef(current: ?ElementFiber, element: ReactElement<any>) :
+  // TODO: This should either be a typed host ref or it should be a typed class
+  // component ref. This should move into the type check that we do in
+  // createFiberFromElementType where we know which one it is.
+  ((handle : any) => void) & { _stringRef: ?string } {
   let mixedRef = element.ref;
   if (mixedRef != null && typeof mixedRef !== 'function') {
     if (element._owner) {
@@ -110,7 +120,7 @@ function coerceRef(current: ?Fiber, element: ReactElement<any>) {
 function ChildReconciler(shouldClone, shouldTrackSideEffects) {
 
   function deleteChild(
-    returnFiber : Fiber,
+    returnFiber : ParentFiber,
     childToDelete : Fiber
   ) : void {
     if (!shouldTrackSideEffects) {
@@ -141,7 +151,7 @@ function ChildReconciler(shouldClone, shouldTrackSideEffects) {
   }
 
   function deleteRemainingChildren(
-    returnFiber : Fiber,
+    returnFiber : ParentFiber,
     currentFirstChild : ?Fiber
   ) : null {
     if (!shouldTrackSideEffects) {
@@ -180,7 +190,7 @@ function ChildReconciler(shouldClone, shouldTrackSideEffects) {
     return existingChildren;
   }
 
-  function useFiber(fiber : Fiber, priority : PriorityLevel) : Fiber {
+  function useFiber<T : Fiber>(fiber : T, priority : PriorityLevel) : T {
     // We currently set sibling to null and index to 0 here because it is easy
     // to forget to do before returning it. E.g. for the single child case.
     if (shouldClone) {
@@ -259,10 +269,17 @@ function ChildReconciler(shouldClone, shouldTrackSideEffects) {
     element : ReactElement<any>,
     priority : PriorityLevel
   ) : Fiber {
-    if (current == null || current.type !== element.type) {
+    if (current == null ||
+        // Verify that this is indeed an element tag
+        current.tag !== HostComponent ||
+        current.tag !== ClassComponent ||
+        current.tag !== FunctionalComponent ||
+        // If it is an element tag, check the type.
+        current.type !== element.type
+        ) {
       // Insert
       const created = createFiberFromElement(element, priority);
-      created.ref = coerceRef(current, element);
+      created.ref = coerceRef(null, element);
       created.return = returnFiber;
       return created;
     } else {
@@ -537,7 +554,7 @@ function ChildReconciler(shouldClone, shouldTrackSideEffects) {
   }
 
   function reconcileChildrenArray(
-    returnFiber : Fiber,
+    returnFiber : ParentFiber,
     currentFirstChild : ?Fiber,
     newChildren : Array<*>,
     priority : PriorityLevel) : ?Fiber {
@@ -863,7 +880,15 @@ function ChildReconciler(shouldClone, shouldTrackSideEffects) {
       // TODO: If key === null and child.key === null, then this only applies to
       // the first item in the list.
       if (child.key === key) {
-        if (child.type === element.type) {
+        if (
+            // Verify that this is indeed an element tag
+            child.tag === HostComponent &&
+            child.tag === ClassComponent &&
+            child.tag === FunctionalComponent &&
+            // And if it is, then compare the type field to validate that we
+            // should indeed update this one.
+            child.type === element.type
+          ) {
           deleteRemainingChildren(returnFiber, child.sibling);
           const existing = useFiber(child, priority);
           existing.ref = coerceRef(child, element);
@@ -881,7 +906,7 @@ function ChildReconciler(shouldClone, shouldTrackSideEffects) {
     }
 
     const created = createFiberFromElement(element, priority);
-    created.ref = coerceRef(currentFirstChild, element);
+    created.ref = coerceRef(null, element);
     created.return = returnFiber;
     return created;
   }